need help with odd CRT monitor image

[John Robertson]

On 2017/07/06 2:22 PM, Ian Field wrote:

mhooker32@gmail.com> wrote in message
news:c5b3309f-f414-4936-bd35-fc7cacbc7c60@googlegroups.com...
On Wednesday, July 5, 2017 at 9:34:41 AM UTC-4, mhoo...@gmail.com wrote:
On Wednesday, July 5, 2017 at 3:39:44 AM UTC-4, John Robertson wrote:
On 2017/07/05 12:35 AM, stratus46@yahoo.com wrote:
And if it has a large value (1000-4700uF) cap inside the feedback
loop that is failing, that can cause severe linearity issues.

G²


Granted, however the OP did say he recapped the monitor and I didn't
want to doubt his statement.

John ;-#)#

its an IC, an LA7833( nte1773) . i'll change it out and see what
happens. i did change out every cap, and it was exactly the same. no
better, no worse.

thanks much

just got done replacing the vertical IC, la7833. no change in the
image. no better, no worse.

There might be a flyback diode lurking nearby - it could've gone leaky.

Flyback diode won't affect the vertical deflection. You will lose the
HOT though if that diode is open. Nowadays they are part of the HOT though.

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

 

[rickman]

mhooker32@gmail.com wrote on 7/6/2017 3:32 PM:

On Thursday, July 6, 2017 at 2:47:59 PM UTC-4, Jeroni Paul wrote:
mhoo...@gmail.com wrote:
https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_manual.pdf

https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_schematic.pdf

B+ is 12v3, 12V and 24V good. i was thinking yoke, but they ohm out good, and look like brand new. no physical damage. looks like a few transistors are after the vertical ic, i'm looking at them now. not real good at following this schematic, so any help is appreciated.

thanks

In the yoke there are two coils for vertical and two for horizontal connected in series or parallel depending on the design, if in parallel one coil connection could be broken. The coils are connected together in the solder posts on the yoke, you may check there if some wire looks loose.

thats a great idea, i didnt know the coils were doubled up. i will check that for sure tonite. i was thinking of inverting the image, there are solder pads for an inverted header on the chassis board, and see what the image does. that would tell me if its the yoke or a chassis issue. does that make sense?

I don't get why your idea is not good. If you can flip the drive signal
polarity the image will invert. If the problem is in the drive circuitry
the half that is working will swap with the half that loses drive. If the
problem is in the yoke the image will invert, but the problem won't. No
need for fancy testers or widgets. Or maybe there is something I don't
understand about this?

--

Rick C

 

[John Robertson]

On 2017/07/06 8:20 PM, rickman wrote:

mhooker32@gmail.com wrote on 7/6/2017 3:32 PM:
On Thursday, July 6, 2017 at 2:47:59 PM UTC-4, Jeroni Paul wrote:
mhoo...@gmail.com wrote:
https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_manual.pdf


https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_schematic.pdf


B+ is 12v3, 12V and 24V good. i was thinking yoke, but they ohm out
good, and look like brand new. no physical damage. looks like a few
transistors are after the vertical ic, i'm looking at them now. not
real good at following this schematic, so any help is appreciated.

thanks

In the yoke there are two coils for vertical and two for horizontal
connected in series or parallel depending on the design, if in
parallel one coil connection could be broken. The coils are connected
together in the solder posts on the yoke, you may check there if some
wire looks loose.

thats a great idea, i didnt know the coils were doubled up. i will
check that for sure tonite. i was thinking of inverting the image,
there are solder pads for an inverted header on the chassis board, and
see what the image does. that would tell me if its the yoke or a
chassis issue. does that make sense?

I don't get why your idea is not good. If you can flip the drive signal
polarity the image will invert. If the problem is in the drive
circuitry the half that is working will swap with the half that loses
drive. If the problem is in the yoke the image will invert, but the
problem won't. No need for fancy testers or widgets. Or maybe there is
something I don't understand about this?

Great point Rick, that would indeed be a good test to see if the yoke is
linear or not.

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

 

On Friday, July 7, 2017 at 12:48:26 AM UTC-4, John Robertson wrote:

On 2017/07/06 8:20 PM, rickman wrote:
mhooker32@gmail.com wrote on 7/6/2017 3:32 PM:
On Thursday, July 6, 2017 at 2:47:59 PM UTC-4, Jeroni Paul wrote:
mhoo...@gmail.com wrote:
https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_manual.pdf


https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_schematic.pdf


B+ is 12v3, 12V and 24V good. i was thinking yoke, but they ohm out
good, and look like brand new. no physical damage. looks like a few
transistors are after the vertical ic, i'm looking at them now. not
real good at following this schematic, so any help is appreciated.

thanks

In the yoke there are two coils for vertical and two for horizontal
connected in series or parallel depending on the design, if in
parallel one coil connection could be broken. The coils are connected
together in the solder posts on the yoke, you may check there if some
wire looks loose.

thats a great idea, i didnt know the coils were doubled up. i will
check that for sure tonite. i was thinking of inverting the image,
there are solder pads for an inverted header on the chassis board, and
see what the image does. that would tell me if its the yoke or a
chassis issue. does that make sense?

I don't get why your idea is not good. If you can flip the drive signal
polarity the image will invert. If the problem is in the drive
circuitry the half that is working will swap with the half that loses
drive. If the problem is in the yoke the image will invert, but the
problem won't. No need for fancy testers or widgets. Or maybe there is
something I don't understand about this?


Great point Rick, that would indeed be a good test to see if the yoke is
linear or not.

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

i soldered a header into the reverse position on the chassis, and gave it a try. it did the same thing as before, just inverted. now the bottom half of the screen has an image that compresses toward the center, a total collapse on the center, and no image in the upper half of the screen. does that rule out a yoke problem?

thanks

 

[John Robertson]

On 2017/07/06 10:04 PM, mhooker32@gmail.com wrote:

On Friday, July 7, 2017 at 12:48:26 AM UTC-4, John Robertson wrote:
On 2017/07/06 8:20 PM, rickman wrote:
mhooker32@gmail.com wrote on 7/6/2017 3:32 PM:
On Thursday, July 6, 2017 at 2:47:59 PM UTC-4, Jeroni Paul wrote:
mhoo...@gmail.com wrote:
https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_manual.pdf


https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_schematic.pdf


B+ is 12v3, 12V and 24V good. i was thinking yoke, but they ohm out
good, and look like brand new. no physical damage. looks like a few
transistors are after the vertical ic, i'm looking at them now. not
real good at following this schematic, so any help is appreciated.

thanks

In the yoke there are two coils for vertical and two for horizontal
connected in series or parallel depending on the design, if in
parallel one coil connection could be broken. The coils are connected
together in the solder posts on the yoke, you may check there if some
wire looks loose.

thats a great idea, i didnt know the coils were doubled up. i will
check that for sure tonite. i was thinking of inverting the image,
there are solder pads for an inverted header on the chassis board, and
see what the image does. that would tell me if its the yoke or a
chassis issue. does that make sense?

I don't get why your idea is not good. If you can flip the drive signal
polarity the image will invert. If the problem is in the drive
circuitry the half that is working will swap with the half that loses
drive. If the problem is in the yoke the image will invert, but the
problem won't. No need for fancy testers or widgets. Or maybe there is
something I don't understand about this?


Great point Rick, that would indeed be a good test to see if the yoke is
linear or not.

John :-#)#


i soldered a header into the reverse position on the chassis, and gave it a try. it did the same thing as before, just inverted. now the bottom half of the screen has an image that compresses toward the center, a total collapse on the center, and no image in the upper half of the screen. does that rule out a yoke problem?

thanks

Based on Rick's points above I think we can rule out the yoke. Nice work
Rick and yourself for that test!

If you have a 'scope then now is a good time to check the outputs of the
LA7851's sawtooth wave generator. Also 'scope the output of the vertical
drive IC to is if it too is still a saw tooth or not. Should swing
pretty much the entire source voltage (24VDC?) if I am not mistaken...

John :-#)#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

 

[John-Del]

On Tuesday, July 4, 2017 at 8:44:59 PM UTC-4, mhoo...@gmail.com wrote:

ive got a tovis mtg-1901cn cga color monitor. in use, or with a test pattern, the image starts out perfectly at the top. as you move down toward the middle , it gradually starts to compress the image, with more compression the closed you get to center. and when it gets to mid screen, its a full vertical collapse. bright while line across the center, with no image whatsoever in the lower 50% of the screen. also sold as a vision pro .

battery voltage is good at 123, 12v and 24 v are good. 123 volts at the flyback.
the vertical output ic is a LA7833. pin 6 has good 24 volt supply, and pin 2 ( output) is a nice 24 v square wave. i recapped the monitor, and the image is exactly the same. now im stuck.

thanks

I didn't read back through all the posts, but if you haven't, check the pump up diode. The anode will be connected to the Vcc and the cathode to the pump up pin of the vert IC. A weak diode here will cause all sorts of havoc (don't check it with a dmm - they often sag under load). Also, I know you said you recapped the monitor, but make sure the yoke coupling capacitor was included. This is typically a high value capacitor (around 1000uf or more).

 

On Friday, July 7, 2017 at 9:52:26 AM UTC-4, John-Del wrote:

On Tuesday, July 4, 2017 at 8:44:59 PM UTC-4, mhoo...@gmail.com wrote:
ive got a tovis mtg-1901cn cga color monitor. in use, or with a test pattern, the image starts out perfectly at the top. as you move down toward the middle , it gradually starts to compress the image, with more compression the closed you get to center. and when it gets to mid screen, its a full vertical collapse. bright while line across the center, with no image whatsoever in the lower 50% of the screen. also sold as a vision pro .

battery voltage is good at 123, 12v and 24 v are good. 123 volts at the flyback.
the vertical output ic is a LA7833. pin 6 has good 24 volt supply, and pin 2 ( output) is a nice 24 v square wave. i recapped the monitor, and the image is exactly the same. now im stuck.

thanks

I didn't read back through all the posts, but if you haven't, check the pump up diode. The anode will be connected to the Vcc and the cathode to the pump up pin of the vert IC. A weak diode here will cause all sorts of havoc (don't check it with a dmm - they often sag under load). Also, I know you said you recapped the monitor, but make sure the yoke coupling capacitor was included. This is typically a high value capacitor (around 1000uf or more).

i may have hit the wall here. pin 14 of the LA7851 is a nice 5v sawtooth. pin 15 is a 12v volts square wave. pin 16 is kind of an ugly bowl shape waveform. pin 17 has nothing. on the la7833 pin 4, which i believe is the input, has the same ugly bowl shape wave, where i think it ought to have a saw tooth? pin two, the output has a very nice 24V square, which i dont think it should have. should be a 24v sawtooth? odd that it puts out a very defined square, instead of just some ugly shape, if something is wrong. i think the pump up is ok, as the output is 24v, but maybe im wrong. im thinking of just replacing the 7851 as a hail mary, and then bailing if that doesnt work.

 

[rickman]

mhooker32@gmail.com wrote on 7/7/2017 10:55 AM:

On Friday, July 7, 2017 at 9:52:26 AM UTC-4, John-Del wrote:
On Tuesday, July 4, 2017 at 8:44:59 PM UTC-4, mhoo...@gmail.com wrote:
ive got a tovis mtg-1901cn cga color monitor. in use, or with a test pattern, the image starts out perfectly at the top. as you move down toward the middle , it gradually starts to compress the image, with more compression the closed you get to center. and when it gets to mid screen, its a full vertical collapse. bright while line across the center, with no image whatsoever in the lower 50% of the screen. also sold as a vision pro .

battery voltage is good at 123, 12v and 24 v are good. 123 volts at the flyback.
the vertical output ic is a LA7833. pin 6 has good 24 volt supply, and pin 2 ( output) is a nice 24 v square wave. i recapped the monitor, and the image is exactly the same. now im stuck.

thanks

I didn't read back through all the posts, but if you haven't, check the pump up diode. The anode will be connected to the Vcc and the cathode to the pump up pin of the vert IC. A weak diode here will cause all sorts of havoc (don't check it with a dmm - they often sag under load). Also, I know you said you recapped the monitor, but make sure the yoke coupling capacitor was included. This is typically a high value capacitor (around 1000uf or more).

i may have hit the wall here. pin 14 of the LA7851 is a nice 5v sawtooth. pin 15 is a 12v volts square wave. pin 16 is kind of an ugly bowl shape waveform. pin 17 has nothing. on the la7833 pin 4, which i believe is the input, has the same ugly bowl shape wave, where i think it ought to have a saw tooth? pin two, the output has a very nice 24V square, which i dont think it should have. should be a 24v sawtooth? odd that it puts out a very defined square, instead of just some ugly shape, if something is wrong. i think the pump up is ok, as the output is 24v, but maybe im wrong. im thinking of just replacing the 7851 as a hail mary, and then bailing if that doesnt work.

This would be a lot easier if you had a working unit to compare waveforms.
It doesn't make sense to me that pin 15 if the LA7851 would be a square
wave. I think I'd try to find something wrong with the parts between pins
15 and 16. Or maybe the components from the LA7833 pin 2 to pin 17 on the
LA7851. I'm guessing this latter circuit is for linearization of the ramp
and might cause the problem you see if a part is bad. It's a bit hard to
figure out what all this does. Looks like the whole thing is pretty highly
optimized.

Are the signals on pin 2 and pin 15 of the two parts the same polarity or
opposite? I can't see how you would get a bowl shape signal on pin 16 if
they are the same. Have you played with the vertical size and linearity
controls to see how they affect the problem?

The charge pump circuit was bothering me as the diode seemed to be
backwards. Then I realized it isn't making 24 volts from 12 volts, it's
pumping up the 24 volts to something higher! What is the voltage on pin 3
of the LA7833? The cap is only rated for 35 volts, so it isn't making 48
volts. But clearly pin 3 should have something on it higher than 24 volts.
What does the pump drive signal on pin 7 look like?

--

Rick C

 

On Friday, July 7, 2017 at 12:09:33 PM UTC-4, rickman wrote:

mhooker32@gmail.com wrote on 7/7/2017 10:55 AM:
On Friday, July 7, 2017 at 9:52:26 AM UTC-4, John-Del wrote:
On Tuesday, July 4, 2017 at 8:44:59 PM UTC-4, mhoo...@gmail.com wrote:
ive got a tovis mtg-1901cn cga color monitor. in use, or with a test pattern, the image starts out perfectly at the top. as you move down toward the middle , it gradually starts to compress the image, with more compression the closed you get to center. and when it gets to mid screen, its a full vertical collapse. bright while line across the center, with no image whatsoever in the lower 50% of the screen. also sold as a vision pro .

battery voltage is good at 123, 12v and 24 v are good. 123 volts at the flyback.
the vertical output ic is a LA7833. pin 6 has good 24 volt supply, and pin 2 ( output) is a nice 24 v square wave. i recapped the monitor, and the image is exactly the same. now im stuck.

thanks

I didn't read back through all the posts, but if you haven't, check the pump up diode. The anode will be connected to the Vcc and the cathode to the pump up pin of the vert IC. A weak diode here will cause all sorts of havoc (don't check it with a dmm - they often sag under load). Also, I know you said you recapped the monitor, but make sure the yoke coupling capacitor was included. This is typically a high value capacitor (around 1000uf or more).

i may have hit the wall here. pin 14 of the LA7851 is a nice 5v sawtooth. pin 15 is a 12v volts square wave. pin 16 is kind of an ugly bowl shape waveform. pin 17 has nothing. on the la7833 pin 4, which i believe is the input, has the same ugly bowl shape wave, where i think it ought to have a saw tooth? pin two, the output has a very nice 24V square, which i dont think it should have. should be a 24v sawtooth? odd that it puts out a very defined square, instead of just some ugly shape, if something is wrong. i think the pump up is ok, as the output is 24v, but maybe im wrong. im thinking of just replacing the 7851 as a hail mary, and then bailing if that doesnt work.

This would be a lot easier if you had a working unit to compare waveforms..
It doesn't make sense to me that pin 15 if the LA7851 would be a square
wave. I think I'd try to find something wrong with the parts between pins
15 and 16. Or maybe the components from the LA7833 pin 2 to pin 17 on the
LA7851. I'm guessing this latter circuit is for linearization of the ramp
and might cause the problem you see if a part is bad. It's a bit hard to
figure out what all this does. Looks like the whole thing is pretty highly
optimized.

Are the signals on pin 2 and pin 15 of the two parts the same polarity or
opposite? I can't see how you would get a bowl shape signal on pin 16 if
they are the same. Have you played with the vertical size and linearity
controls to see how they affect the problem?

The charge pump circuit was bothering me as the diode seemed to be
backwards. Then I realized it isn't making 24 volts from 12 volts, it's
pumping up the 24 volts to something higher! What is the voltage on pin 3
of the LA7833? The cap is only rated for 35 volts, so it isn't making 48
volts. But clearly pin 3 should have something on it higher than 24 volts.
What does the pump drive signal on pin 7 look like?

--

Rick C

pin 3 of 7833 is 25.65 v. pins 2 and 15 are opposite polarity. pump drive signal is a .5 volts upside down sawtooth.

i appreciate the time taken here. i could just send this out, but i think i am close, just not there.

 

Ramp generator, probably at whatever that unit's equivalent of a jungle IC is. An IC is only as good as what is fed into it. Yoke problems are rare and thus unlikely.

You need a proper sawtooth wave driving that IC or it will not put out what you want. It is that simple. So go backwards and find that ramp generator. If you cannot find it, put up a link to the print and I will. If you do, please use something that an older PC can use.

 

[rickman]

mhooker32@gmail.com wrote on 7/7/2017 1:01 PM:

On Friday, July 7, 2017 at 12:09:33 PM UTC-4, rickman wrote:

The charge pump circuit was bothering me as the diode seemed to be
backwards. Then I realized it isn't making 24 volts from 12 volts, it's
pumping up the 24 volts to something higher! What is the voltage on pin 3
of the LA7833? The cap is only rated for 35 volts, so it isn't making 48
volts. But clearly pin 3 should have something on it higher than 24 volts.
What does the pump drive signal on pin 7 look like?

--

Rick C

pin 3 of 7833 is 25.65 v. pins 2 and 15 are opposite polarity. pump drive signal is a .5 volts upside down sawtooth.

i appreciate the time taken here. i could just send this out, but i think i am close, just not there.

If pin 7 pump drive signal is only half a volt, I would say your problem is
there. Pin 3 should clearly be more than 25 volts and it is this signal
that drives that voltage. Is pin 3 at all steady or is it also a waveform?
You should measure the voltage with the scope, not the meter. They don't
use a smoothing cap so I guess the voltage will pulse with the drive.
During retrace you don't need a high voltage on pin 3. Retrace is when the
voltage goes below 24 volts and the diode is forward biased to charge up the
cap again.

I think you said you already replaced the LA7833, so there are only two
other parts. When you say pin 7 is "upside down", do you mean it is
normally high and drops low or it is going negative? I would expect it to
be near 24 volts during the picture time and drops low during retrace as the
cap charges. I guess the question is how does the waveform on pin 3 look?
I would expect it mostly near 48 volts dropping slightly below 24 volts
during retrace. Pin 7 should definitely have a significant pulse voltage on
it.

--

Rick C

 

[John Robertson]

On 2017/07/07 10:01 AM, mhooker32@gmail.com wrote:

On Friday, July 7, 2017 at 12:09:33 PM UTC-4, rickman wrote:
mhooker32@gmail.com wrote on 7/7/2017 10:55 AM:
On Friday, July 7, 2017 at 9:52:26 AM UTC-4, John-Del wrote:
On Tuesday, July 4, 2017 at 8:44:59 PM UTC-4, mhoo...@gmail.com wrote:
ive got a tovis mtg-1901cn cga color monitor. in use, or with a test pattern, the image starts out perfectly at the top. as you move down toward the middle , it gradually starts to compress the image, with more compression the closed you get to center. and when it gets to mid screen, its a full vertical collapse. bright while line across the center, with no image whatsoever in the lower 50% of the screen. also sold as a vision pro .

battery voltage is good at 123, 12v and 24 v are good. 123 volts at the flyback.
the vertical output ic is a LA7833. pin 6 has good 24 volt supply, and pin 2 ( output) is a nice 24 v square wave. i recapped the monitor, and the image is exactly the same. now im stuck.

thanks

I didn't read back through all the posts, but if you haven't, check the pump up diode. The anode will be connected to the Vcc and the cathode to the pump up pin of the vert IC. A weak diode here will cause all sorts of havoc (don't check it with a dmm - they often sag under load). Also, I know you said you recapped the monitor, but make sure the yoke coupling capacitor was included. This is typically a high value capacitor (around 1000uf or more).

i may have hit the wall here. pin 14 of the LA7851 is a nice 5v sawtooth. pin 15 is a 12v volts square wave. pin 16 is kind of an ugly bowl shape waveform. pin 17 has nothing. on the la7833 pin 4, which i believe is the input, has the same ugly bowl shape wave, where i think it ought to have a saw tooth? pin two, the output has a very nice 24V square, which i dont think it should have. should be a 24v sawtooth? odd that it puts out a very defined square, instead of just some ugly shape, if something is wrong. i think the pump up is ok, as the output is 24v, but maybe im wrong. im thinking of just replacing the 7851 as a hail mary, and then bailing if that doesnt work.

This would be a lot easier if you had a working unit to compare waveforms..
It doesn't make sense to me that pin 15 if the LA7851 would be a square
wave. I think I'd try to find something wrong with the parts between pins
15 and 16. Or maybe the components from the LA7833 pin 2 to pin 17 on the
LA7851. I'm guessing this latter circuit is for linearization of the ramp
and might cause the problem you see if a part is bad. It's a bit hard to
figure out what all this does. Looks like the whole thing is pretty highly
optimized.

Are the signals on pin 2 and pin 15 of the two parts the same polarity or
opposite? I can't see how you would get a bowl shape signal on pin 16 if
they are the same. Have you played with the vertical size and linearity
controls to see how they affect the problem?

The charge pump circuit was bothering me as the diode seemed to be
backwards. Then I realized it isn't making 24 volts from 12 volts, it's
pumping up the 24 volts to something higher! What is the voltage on pin 3
of the LA7833? The cap is only rated for 35 volts, so it isn't making 48
volts. But clearly pin 3 should have something on it higher than 24 volts.
What does the pump drive signal on pin 7 look like?

--

Rick C

pin 3 of 7833 is 25.65 v. pins 2 and 15 are opposite polarity. pump drive signal is a .5 volts upside down sawtooth.

i appreciate the time taken here. i could just send this out, but i think i am close, just not there.

Afraid we don't have one on the service bench otherwise I would be happy
to send you waveform images. One of those monitors is in my storage area
I'm pretty sure, but...


John :-#(#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

 

[Ian Field]

"John Robertson" <spam@flippers.com> wrote in message
news:3rudnUQ-koXXLMPEnZ2dnUU7-RPNnZ2d@giganews.com...

On 2017/07/06 2:26 PM, Ian Field wrote:


"John-Del" <ohger1s@gmail.com> wrote in message
news:514af99a-2f1b-41a7-8a6b-dc0dea0292ca@googlegroups.com...
On Thursday, July 6, 2017 at 11:18:38 AM UTC-4, mhoo...@gmail.com wrote:
On Thursday, July 6, 2017 at 7:17:12 AM UTC-4, rickman wrote:
mhooker32@gmail.com wrote on 7/6/2017 1:00 AM:
On Wednesday, July 5, 2017 at 9:34:41 AM UTC-4, mhoo...@gmail.com
wrote:
On Wednesday, July 5, 2017 at 3:39:44 AM UTC-4, John Robertson
wrote:
On 2017/07/05 12:35 AM, stratus46@yahoo.com wrote:
And if it has a large value (1000-4700uF) cap inside the
feedback > >>>> loop that is failing, that can cause severe linearity
issues.

G²


Granted, however the OP did say he recapped the monitor and I
didn't
want to doubt his statement.

John ;-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

its an IC, an LA7833( nte1773) . i'll change it out and see what
happens. i did change out every cap, and it was exactly the
same. no > >> better, no worse.

thanks much

just got done replacing the vertical IC, la7833. no change in the
image. no better, no worse.

Looks like the 24 volt supply is generated by doubling the 12 volt
supply.
Measure the 24 volt supply at pin 6. I bet something is wrong that
this is
only 12 volts, maybe the diode?

--
Rick C


https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_manual.pdf

https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_schematic.pdf

B+ is 12v3, 12V and 24V good. i was thinking yoke, but they ohm out
good, and look like brand new. no physical damage.

Not saying the yoke is the problem, but a single turn shorted to an
adjacent turn will not change the resistance reading on your dmm, but a
single shorted turn will totally collapse the magnetic field of the
coil.

A ringer is the best instrument to check for shorted turns.

DSE did one, but I don't think the kit is available anymore.

The schematic is floating about and there's no unobtanium in the parts
list.

The old DS ringer was designed by Bob Parker and was best for checking
flybacks (LOPTs), not much use on yokes I'm afraid. The kit is now made by
Anatek (we carry it on Flippers), but you would be better off with an
inductance meter - split the vertical windings and each side should be
identical.

I tried the DSE ringer on pretty much anything laying around - it doesn't
like very low inductances.

Scan yokes should be fine.

 

[Ian Field]

"John Robertson" <spam@flippers.com> wrote in message
news:3rudnUc-koUQLMPEnZ2dnUU7-ROdnZ2d@giganews.com...

On 2017/07/06 2:22 PM, Ian Field wrote:


mhooker32@gmail.com> wrote in message
news:c5b3309f-f414-4936-bd35-fc7cacbc7c60@googlegroups.com...
On Wednesday, July 5, 2017 at 9:34:41 AM UTC-4, mhoo...@gmail.com wrote:
On Wednesday, July 5, 2017 at 3:39:44 AM UTC-4, John Robertson wrote:
On 2017/07/05 12:35 AM, stratus46@yahoo.com wrote:
And if it has a large value (1000-4700uF) cap inside the feedback
loop that is failing, that can cause severe linearity issues.

G²


Granted, however the OP did say he recapped the monitor and I didn't
want to doubt his statement.

John ;-#)#

its an IC, an LA7833( nte1773) . i'll change it out and see what
happens. i did change out every cap, and it was exactly the same. no
better, no worse.

thanks much

just got done replacing the vertical IC, la7833. no change in the image.
no better, no worse.

There might be a flyback diode lurking nearby - it could've gone leaky.

Flyback diode won't affect the vertical deflection. You will lose the HOT
though if that diode is open. Nowadays they are part of the HOT though.

The one in the vertical output section can and does.

 

[Ian Field]

"John Robertson" <spam@flippers.com> wrote in message
news:ComdnW2tcfL-SMLEnZ2dnUU7-L3NnZ2d@giganews.com...

On 2017/07/07 10:01 AM, mhooker32@gmail.com wrote:
On Friday, July 7, 2017 at 12:09:33 PM UTC-4, rickman wrote:
mhooker32@gmail.com wrote on 7/7/2017 10:55 AM:
On Friday, July 7, 2017 at 9:52:26 AM UTC-4, John-Del wrote:
On Tuesday, July 4, 2017 at 8:44:59 PM UTC-4, mhoo...@gmail.com wrote:
ive got a tovis mtg-1901cn cga color monitor. in use, or with a test
pattern, the image starts out perfectly at the top. as you move down
toward the middle , it gradually starts to compress the image, with
more compression the closed you get to center. and when it gets to
mid screen, its a full vertical collapse. bright while line across
the center, with no image whatsoever in the lower 50% of the screen.
also sold as a vision pro .

battery voltage is good at 123, 12v and 24 v are good. 123 volts at
the flyback.
the vertical output ic is a LA7833. pin 6 has good 24 volt supply,
and pin 2 ( output) is a nice 24 v square wave. i recapped the
monitor, and the image is exactly the same. now im stuck.

thanks

I didn't read back through all the posts, but if you haven't, check
the pump up diode. The anode will be connected to the Vcc and the
cathode to the pump up pin of the vert IC. A weak diode here will
cause all sorts of havoc (don't check it with a dmm - they often sag
under load). Also, I know you said you recapped the monitor, but make
sure the yoke coupling capacitor was included. This is typically a
high value capacitor (around 1000uf or more).

i may have hit the wall here. pin 14 of the LA7851 is a nice 5v
sawtooth. pin 15 is a 12v volts square wave. pin 16 is kind of an ugly
bowl shape waveform. pin 17 has nothing. on the la7833 pin 4, which i
believe is the input, has the same ugly bowl shape wave, where i think
it ought to have a saw tooth? pin two, the output has a very nice 24V
square, which i dont think it should have. should be a 24v sawtooth?
odd that it puts out a very defined square, instead of just some ugly
shape, if something is wrong. i think the pump up is ok, as the output
is 24v, but maybe im wrong. im thinking of just replacing the 7851 as
a hail mary, and then bailing if that doesnt work.

This would be a lot easier if you had a working unit to compare
waveforms..
It doesn't make sense to me that pin 15 if the LA7851 would be a square
wave. I think I'd try to find something wrong with the parts between
pins
15 and 16. Or maybe the components from the LA7833 pin 2 to pin 17 on
the
LA7851. I'm guessing this latter circuit is for linearization of the
ramp
and might cause the problem you see if a part is bad. It's a bit hard
to
figure out what all this does. Looks like the whole thing is pretty
highly
optimized.

Are the signals on pin 2 and pin 15 of the two parts the same polarity
or
opposite? I can't see how you would get a bowl shape signal on pin 16
if
they are the same. Have you played with the vertical size and linearity
controls to see how they affect the problem?

The charge pump circuit was bothering me as the diode seemed to be
backwards. Then I realized it isn't making 24 volts from 12 volts, it's
pumping up the 24 volts to something higher! What is the voltage on pin
3
of the LA7833? The cap is only rated for 35 volts, so it isn't making
48
volts. But clearly pin 3 should have something on it higher than 24
volts.
What does the pump drive signal on pin 7 look like?

--

Rick C

pin 3 of 7833 is 25.65 v. pins 2 and 15 are opposite polarity. pump
drive signal is a .5 volts upside down sawtooth.

i appreciate the time taken here. i could just send this out, but i think
i am close, just not there.


Afraid we don't have one on the service bench otherwise I would be happy
to send you waveform images. One of those monitors is in my storage area
I'm pretty sure, but...

Pretty sure you can wire up an adaptor to run VGA off a CGA output - for
some strange reason, many VGA monitors aren't backward compatible with EGA.

 

[John Robertson]

On 2017/07/07 1:52 PM, Ian Field wrote:

"John Robertson" <spam@flippers.com> wrote in message
news:ComdnW2tcfL-SMLEnZ2dnUU7-L3NnZ2d@giganews.com...
On 2017/07/07 10:01 AM, mhooker32@gmail.com wrote:
On Friday, July 7, 2017 at 12:09:33 PM UTC-4, rickman wrote:
mhooker32@gmail.com wrote on 7/7/2017 10:55 AM:
On Friday, July 7, 2017 at 9:52:26 AM UTC-4, John-Del wrote:
On Tuesday, July 4, 2017 at 8:44:59 PM UTC-4, mhoo...@gmail.com
wrote:
ive got a tovis mtg-1901cn cga color monitor. in use, or with a
test pattern, the image starts out perfectly at the top. as you
move down toward the middle , it gradually starts to compress the
image, with more compression the closed you get to center. and
when it gets to mid screen, its a full vertical collapse. bright
while line across the center, with no image whatsoever in the
lower 50% of the screen. also sold as a vision pro .

battery voltage is good at 123, 12v and 24 v are good. 123 volts
at the flyback.
the vertical output ic is a LA7833. pin 6 has good 24 volt
supply, and pin 2 ( output) is a nice 24 v square wave. i
recapped the monitor, and the image is exactly the same. now im
stuck.

thanks

I didn't read back through all the posts, but if you haven't,
check the pump up diode. The anode will be connected to the Vcc
and the cathode to the pump up pin of the vert IC. A weak diode
here will cause all sorts of havoc (don't check it with a dmm -
they often sag under load). Also, I know you said you recapped
the monitor, but make sure the yoke coupling capacitor was
included. This is typically a high value capacitor (around 1000uf
or more).

i may have hit the wall here. pin 14 of the LA7851 is a nice 5v
sawtooth. pin 15 is a 12v volts square wave. pin 16 is kind of an
ugly bowl shape waveform. pin 17 has nothing. on the la7833 pin 4,
which i believe is the input, has the same ugly bowl shape wave,
where i think it ought to have a saw tooth? pin two, the output
has a very nice 24V square, which i dont think it should have.
should be a 24v sawtooth? odd that it puts out a very defined
square, instead of just some ugly shape, if something is wrong. i
think the pump up is ok, as the output is 24v, but maybe im wrong.
im thinking of just replacing the 7851 as a hail mary, and then
bailing if that doesnt work.

This would be a lot easier if you had a working unit to compare
waveforms..
It doesn't make sense to me that pin 15 if the LA7851 would be a square
wave. I think I'd try to find something wrong with the parts
between pins
15 and 16. Or maybe the components from the LA7833 pin 2 to pin 17
on the
LA7851. I'm guessing this latter circuit is for linearization of
the ramp
and might cause the problem you see if a part is bad. It's a bit
hard to
figure out what all this does. Looks like the whole thing is pretty
highly
optimized.

Are the signals on pin 2 and pin 15 of the two parts the same
polarity or
opposite? I can't see how you would get a bowl shape signal on pin
16 if
they are the same. Have you played with the vertical size and
linearity
controls to see how they affect the problem?

The charge pump circuit was bothering me as the diode seemed to be
backwards. Then I realized it isn't making 24 volts from 12 volts,
it's
pumping up the 24 volts to something higher! What is the voltage on
pin 3
of the LA7833? The cap is only rated for 35 volts, so it isn't
making 48
volts. But clearly pin 3 should have something on it higher than 24
volts.
What does the pump drive signal on pin 7 look like?

--

Rick C

pin 3 of 7833 is 25.65 v. pins 2 and 15 are opposite polarity.
pump drive signal is a .5 volts upside down sawtooth.

i appreciate the time taken here. i could just send this out, but i
think i am close, just not there.


Afraid we don't have one on the service bench otherwise I would be
happy to send you waveform images. One of those monitors is in my
storage area I'm pretty sure, but...

Pretty sure you can wire up an adaptor to run VGA off a CGA output - for
some strange reason, many VGA monitors aren't backward compatible with EGA.

There are CGA -> VGA adapters on eBay all the time. Cheap. Most work,
some don't so do some research first.

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

 

On Friday, July 7, 2017 at 1:24:17 PM UTC-4, jurb...@gmail.com wrote:

Ramp generator, probably at whatever that unit's equivalent of a jungle IC is. An IC is only as good as what is fed into it. Yoke problems are rare and thus unlikely.

You need a proper sawtooth wave driving that IC or it will not put out what you want. It is that simple. So go backwards and find that ramp generator. If you cannot find it, put up a link to the print and I will. If you do, please use something that an older PC can use.

https://na.suzohapp.com/pdf/service_pdfs/support/visionpro/49-1329-vp2_schematic.pdf

 

[Dimitrij Klingbeil]

On 07.07.2017 19:36, rickman wrote:

mhooker32@gmail.com wrote on 7/7/2017 1:01 PM:
On Friday, July 7, 2017 at 12:09:33 PM UTC-4, rickman wrote:

The charge pump circuit was bothering me as the diode seemed to be
backwards. Then I realized it isn't making 24 volts from 12 volts, it's
pumping up the 24 volts to something higher! What is the voltage on
pin 3
of the LA7833? The cap is only rated for 35 volts, so it isn't
making 48
volts. But clearly pin 3 should have something on it higher than 24
volts.
What does the pump drive signal on pin 7 look like?

--

Rick C

pin 3 of 7833 is 25.65 v. pins 2 and 15 are opposite polarity. pump
drive signal is a .5 volts upside down sawtooth.

i appreciate the time taken here. i could just send this out, but i
think i am close, just not there.

If pin 7 pump drive signal is only half a volt, I would say your problem
is there. Pin 3 should clearly be more than 25 volts and it is this
signal that drives that voltage. Is pin 3 at all steady or is it also a
waveform? You should measure the voltage with the scope, not the meter.
They don't use a smoothing cap so I guess the voltage will pulse with
the drive. During retrace you don't need a high voltage on pin 3.
Retrace is when the voltage goes below 24 volts and the diode is forward
biased to charge up the cap again.

I think you said you already replaced the LA7833, so there are only two
other parts. When you say pin 7 is "upside down", do you mean it is
normally high and drops low or it is going negative? I would expect it
to be near 24 volts during the picture time and drops low during retrace
as the cap charges. I guess the question is how does the waveform on
pin 3 look? I would expect it mostly near 48 volts dropping slightly
below 24 volts during retrace. Pin 7 should definitely have a
significant pulse voltage on it.

Did you check D360 (the "bootstrap" diode from 24V in the pump circuit)?

It may be shorted and pulling the "pumped" supply "down" to 24V. The IC
will most likely need the pumped supply for one half of the screen only.

 

[Dimitrij Klingbeil]

On 06.07.2017 23:18, mhooker32@gmail.com wrote:

On Thursday, July 6, 2017 at 3:58:22 PM UTC-4, John-Del wrote:
A ringer is the best instrument to check for shorted turns.

not sure what a ringer is, but im pretty sure i dont have one. you
mean like a tone generator, and you move it around the yoke ?

Look up "impulse winding tester", that's the high voltage version.
Ring testers work the same way, with V rather than kV scale drive.

 

On Saturday, July 8, 2017 at 7:15:05 PM UTC-4, Dimitrij Klingbeil wrote:

On 07.07.2017 19:36, rickman wrote:
mhooker32@gmail.com wrote on 7/7/2017 1:01 PM:
On Friday, July 7, 2017 at 12:09:33 PM UTC-4, rickman wrote:

The charge pump circuit was bothering me as the diode seemed to be
backwards. Then I realized it isn't making 24 volts from 12 volts, it's
pumping up the 24 volts to something higher! What is the voltage on
pin 3
of the LA7833? The cap is only rated for 35 volts, so it isn't
making 48
volts. But clearly pin 3 should have something on it higher than 24
volts.
What does the pump drive signal on pin 7 look like?

--

Rick C

pin 3 of 7833 is 25.65 v. pins 2 and 15 are opposite polarity. pump
drive signal is a .5 volts upside down sawtooth.

i appreciate the time taken here. i could just send this out, but i
think i am close, just not there.

If pin 7 pump drive signal is only half a volt, I would say your problem
is there. Pin 3 should clearly be more than 25 volts and it is this
signal that drives that voltage. Is pin 3 at all steady or is it also a
waveform? You should measure the voltage with the scope, not the meter.
They don't use a smoothing cap so I guess the voltage will pulse with
the drive. During retrace you don't need a high voltage on pin 3.
Retrace is when the voltage goes below 24 volts and the diode is forward
biased to charge up the cap again.

I think you said you already replaced the LA7833, so there are only two
other parts. When you say pin 7 is "upside down", do you mean it is
normally high and drops low or it is going negative? I would expect it
to be near 24 volts during the picture time and drops low during retrace
as the cap charges. I guess the question is how does the waveform on
pin 3 look? I would expect it mostly near 48 volts dropping slightly
below 24 volts during retrace. Pin 7 should definitely have a
significant pulse voltage on it.

Did you check D360 (the "bootstrap" diode from 24V in the pump circuit)?

It may be shorted and pulling the "pumped" supply "down" to 24V. The IC
will most likely need the pumped supply for one half of the screen only.

i did pull up one leg of D360 and checked it, it checked good. pin 7 never goes anywhere near 24 volt. there is a .5 volts poorly defined waveform, almost looks like ripple. im thinking it should be a 24v sawtooth? i am thinking something on the board may be pulling down pin 7?

thanks