Reducing HV output voltage from Flyback/LOPT as used in arca

[Terry Schwartz]

It is not just the face of the tube that emits X-Rays, the glass on the
bell housing can (I am pretty sure) leak as well. A common use for this
13" monitor was in cocktail tables. So the face of the tube is shown to
the players and the bell housing, well let us just say it is pretty much
inline with your waist on down...

Not wanting customer gonads to glow in the dark was my main impetus for
finding a simple, yet reliable solution that did not defeat the internal
over-voltage X-ray shutdown process.

John, my DK JR cocktail is in a metal cabinet -- robust as all get-out. Are my gonads safe in the case of HV runaway? Not that I need them anymore, my breeding days are long past.

Actually I do believe that it's the accelerated electrons hitting the face of the tube that causes X-ray radiation. Any radiation out the sides is very low energy and likely stopped by the cabinet or maybe even the aquadag.

However -- excess high voltage used to cause CRT images to "bloom". Isn't that happening in your scenario?

Terry

 

[John Robertson]

On 2018/06/06 12:14 PM, Terry Schwartz wrote:

catastrophic failure likely to wreck the envelope so it cannot be rebuilt.

Rebuilt? Seriously? I think the last CRT rebuilder went out of business about a decade ago. Hawkeye. The only rebuilding operation left in the western world is in the Vintage TV museum, and that's only for show.

I think many arcade machines now are repaired by subbing in an LCD panel from a computer monitor. I've seen several, and they work great. Sometimes a small circuit board is required to invert polarities, etc., but there are a handful of guys selling those on line.

John, have you considered the LCD sub?

Terry

We are trying to avoid going LCD, the original picture tube is just
fine, and gives a more realistic image on the customer's cabaret style
Pacman game. LCDs are flat, picture tubes were mostly curved.

We do do LCD conversions, but the reason I started this investigation is
other folks also like to repair monitors and when I realized a potential
risk I decided to do something about it.

FYI, we still have over 100 monitors in our shop in various states from
NOS to POS (Peace Of S...) that we plan to save as many as possible for
museums and collectors who are our customers.

John :-#)#

PS, there are people who are rebuilding picture tubes in their
garages...small tubes for early sets, but it is only a matter of time
before they progress to larger tubes - if there is a market!

--
(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 Wednesday, June 6, 2018 at 4:21:50 PM UTC-4, John Robertson wrote:

On 2018/06/06 12:14 PM, Terry Schwartz wrote:
catastrophic failure likely to wreck the envelope so it cannot be rebuilt.

Rebuilt? Seriously? I think the last CRT rebuilder went out of business about a decade ago. Hawkeye. The only rebuilding operation left in the western world is in the Vintage TV museum, and that's only for show.

I think many arcade machines now are repaired by subbing in an LCD panel from a computer monitor. I've seen several, and they work great. Sometimes a small circuit board is required to invert polarities, etc., but there are a handful of guys selling those on line.

John, have you considered the LCD sub?

Terry


We are trying to avoid going LCD, the original picture tube is just
fine, and gives a more realistic image on the customer's cabaret style
Pacman game. LCDs are flat, picture tubes were mostly curved.

We do do LCD conversions, but the reason I started this investigation is
other folks also like to repair monitors and when I realized a potential
risk I decided to do something about it.

FYI, we still have over 100 monitors in our shop in various states from
NOS to POS (Peace Of S...) that we plan to save as many as possible for
museums and collectors who are our customers.

John :-#)#

PS, there are people who are rebuilding picture tubes in their
garages...small tubes for early sets, but it is only a matter of time
before they progress to larger tubes - if there is a market!

--
(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."

Back in the 70s there were several companies that sold CRT rebuilding equipment out of the back of Radio Electronics and Electronic Servicing (and others). I came real close to buying one of those setups. I'm sure many others did and I'm sure some of the machines are still around, but the big problem would be sourcing the gun assy. For all we know, the Ruskies might still be making them.

 

[John Robertson]

On 2018/06/06 2:11 PM, John-Del wrote:

On Wednesday, June 6, 2018 at 4:21:50 PM UTC-4, John Robertson wrote:
On 2018/06/06 12:14 PM, Terry Schwartz wrote:
catastrophic failure likely to wreck the envelope so it cannot be rebuilt.

Rebuilt? Seriously? I think the last CRT rebuilder went out of business about a decade ago. Hawkeye. The only rebuilding operation left in the western world is in the Vintage TV museum, and that's only for show.

I think many arcade machines now are repaired by subbing in an LCD panel from a computer monitor. I've seen several, and they work great. Sometimes a small circuit board is required to invert polarities, etc., but there are a handful of guys selling those on line.

John, have you considered the LCD sub?

Terry


We are trying to avoid going LCD, the original picture tube is just
fine, and gives a more realistic image on the customer's cabaret style
Pacman game. LCDs are flat, picture tubes were mostly curved.

We do do LCD conversions, but the reason I started this investigation is
other folks also like to repair monitors and when I realized a potential
risk I decided to do something about it.

FYI, we still have over 100 monitors in our shop in various states from
NOS to POS (Peace Of S...) that we plan to save as many as possible for
museums and collectors who are our customers.

John :-#)#

PS, there are people who are rebuilding picture tubes in their
garages...small tubes for early sets, but it is only a matter of time
before they progress to larger tubes - if there is a market!

--

Back in the 70s there were several companies that sold CRT rebuilding equipment out of the back of Radio Electronics and Electronic Servicing (and others). I came real close to buying one of those setups. I'm sure many others did and I'm sure some of the machines are still around, but the big problem would be sourcing the gun assy. For all we know, the Ruskies might still be making them.

People rebuild radio and other tubes, pretty sure a gun can be rebuilt -
if worth enough $$ to someone!

And here you go!

https://www.youtube.com/watch?v=W3G7b-DcOO4

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 Robertson]

On 2018/06/05 9:48 PM, jurb6006@gmail.com wrote:

Nice to find someone willing put put effort into shit like this. I commend it. And to use pretty high tech skills to do it, like about engineers level, modifications and KNOWING what works right and doesn't. Have any idea how hard it is to find people who CAN do that, let alone willing ? Keep it alive bro... (het, sounds like a good name for a company)

I'll put my suggestions first and commentary later to be sufferable...

The components around R 516, C 519 etc. have nothing to do with the HV level. They are for the ABL, they measure the actual HV current and cut the video gain down if it exceeds a certain level. There is not supposed to be voltage dropped there like in a CRO.

Notice the difference in the print around C 512 - 514. The 19" version has 2 extra caps there. They downed C 514 down to 2,ooo pF from 2,500. Then they added C 531 & 532. which slows down the retrace, makes all retrace rectified sources lower and trace rectified sources a little bit higher. You can tell which it is by scoping the input the the rectifier, if you see a large negative trace on a positive source it is trace rectified, if the pulse is positive on a positive source it is retrace rectified.

Question : this potted fly, CAN YOU GET TO THE CORE ? You do not have to get to the windings, if you can get to the core you can add bucking or boosting windings to any winding there. All that area that is encapsulated, can you see the ferrite thing around it ? If so, can you see a gap ? All we need is about 0.03 inches for good enough. That is big enough for # 24 AWG to get through and you can get it with like couple hundred volt insulation.

The outside core is accessible, and there is a nice gap between it and
the potted windings.

ftp://flippers.com//usr/www/users/flip/pdfs/Temp/Electrohome_GO-7_13inch_CBO_flyback.jpg

Increasing the capacitance alone might not do it, but a combination of changing the B+ and that might.

Comment :

This thing was built before internal pincusion correction in the CRTs. There is a saturable reactor and another one that is permanent magnet biased. there are also VDRs. This means that This indicated that voltage and current levels muct be at least close for good geometry. We are not talking moon shot accuracy here but we must remain within the "linear non-linearitiy" operating range of those devices.

It also seems that the B+ is lower in one than the other.; One says (somewhere) 120 regulated and the other says nothing, but both shutdown use the same resistors and Zeners, and that indicates that the B+ level is close if not the same.

Both 13 & 19" used 120VDC as their B+. The 19" regulator was simply
higher current.

If, after adding the capacitance I suggested you find that it is not enough then the next thing is to reduce the B+. but don't do it with a passive device. The best method would be to add a Zener diode of the voltage desired with the anode to ground and the cathode to to the junction of C 905 & R 914. You'll probably want to choose a standard value anyway so choose a lower one and put a pot in series. It might decrease the tightness of the regulation but bucking that we had the gain of the IC itself. Look at most of them, they try to operate in their linear range. That works to our advantage.

Capacitance of 6,000pf did work, the buck/boost idea is nice, but may
involve too much time, and it will be easy for someone to get wrong. A
single cap is nice and clean and almost fool-proof. I still have to
track down an original flyback driven 13" monitor to make sure the other
voltages (with the 6Kpf cap) are within reasonable limits, but the image
is good, so I assume all is well! The filament, screen, and focus
voltages all seem good, so I think we have a winner here. Will now try
doing a second monitor to see if this is not just a fluke...

Keep this baby on the road !

That is what we do at my shop!

Thanks for all your technical advice, that has clarified the schematic a
lot for me, obviously you have experience with either designing or
repairing monitors/TVs.

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."

 

>"The outside core is accessible, and there is a nice gap between it and the potted windings. "

It can be a chance getting the polarity right when you buck/boost, but with a fly (LOPT) like that it is easy to see on the scope. I wanted to buck the pulse to the yoke on this little 13" Sony I watch sometimes, I didn't buck the top end where the 1,000 volt pulse is, I bucked the bottom. Makes more sense.

"Both 13 & 19" used 120VDC as their B+. The 19" regulator was simply
higher current. "

Makes sense by backward reasoning. Shutdown is the same, there is a law or something that it must when the radiation hits a certain level and that is that. Thus, a unit with more nominal B+ will have a higher OV shutdown threshold.

>"Capacitance of 6,000pf did work..."

It is possible it is perfect. For market share in the repair parts market they do occlude the fact that some of these parts are the same. Your average tech has no way of telling even with the best of equipment. And teachers can't teach what they do not know. they offered me a job, well one guy who worked at Case University. he said they can't find anyone to teach what I taught him to get the job there, and that was very basic. the traveling turned me off but I might take it now, however they must take me with absolutely zero accreditation, official anyway.

"I still have to
track down an original flyback driven 13" monitor to make sure the other voltages (with the 6Kpf cap) are within reasonable limits"

There appears to only be one scan derived source, 12 volts. They do not change the number of turns on one winding of a transformer for different screen sizes. It is almost for sure well within specs. think about it from the engineers' point of view.;

>"That is what we do at my shop! "

Good. would you like some references to some music ? Judas Priest - Another Thing Comin', Queensryche - Best Man, there are more. I odn't give up. Well as a rule, sometimes I see no way to get er done and then I pull out faster than a (insert your own thaing here)

>"Thanks for all your technical advice, that has clarified the schematic a lot for me, obviously you have experience with either designing or repairing monitors/TVs. "

Not designing so much, but I have made alot of money making things work that nobody else could. Part not available ? They called me. I was good. We had a bunch of countdown chips that were bad out of the box. No sync. With the addition of a generic PNP transistor I fixed it and the sets ran fine on the defective IC. I have modified more power supplies than they have designed. when I put a winding on a fly (LOPT) to isolate the filament of a CRT with an HK short I used a resistor of like 5K to make sure it was effectively shorted and not intermittent (which many were) and then boosted the high frequency response of the video amp to compensate for the stray capacitance introduced by the video being imposed on the line.

At one time, I considered a big shop. I have been in business but it only got to 2 locations and we got sick of it. But I considered a test for tech applicants. One of the first requirements is to be able to draw a block diagram of a color TV. And I don't mean 3 blocks, I mean with some detail.

From your posts I am pretty sure you can, but how many can ? Or could ? So many places had incompetent people it left a bad taste in the customers. Where I worked we were cheaper and better because we were more efficient, and ALSO MADE MORE MONEY. Competence pays off if you know how to use it.