Toshiba TV29C90 problem; Image fades to black...

[G]

Howdy Budgie....right you are.....thats not being a spoiler but
just being helpful . Must admit I based my experience has been with
the positive VR's (obvious eh!). Having said that......the tab of a
79xx wouldn't necessarily need to be insulated but it has to be kept in
mind for sure. (anyone here ever tried building their regulator into a
grounded side of a rectifier heheh......it works just fine - just looks
disconcerting when you look at the diagram).

 

[Scrim]

"Andy Cuffe" <acuffe@gmail.com> wrote in message
news:0vo4229i45huqm8i0cg9cac1io9t5vcc9b@4ax.com...

On Wed, 22 Mar 2006 17:26:21 GMT, "Scrim" <nospam@nospam.com> wrote:

The only other possibility I can think of is if they do have separate
horizontal and vertical focus

They do in fact have separate horizontal and vertical focus. The two
interact slightly, so if it goes out of horizontal focus, the vertical
focus will also be affected.

I had a 21" Sony with a CRT that would intermittently go way out of
focus in the horizontal direction. Sometimes it was unusable, but it
often went for weeks without a problem. Normally it would only snap
out of focus for a second or two every few days. I eventually
replaced the CRT with one from a scrap monitor and it's been working
fine for a couple of years.
Andy Cuffe

acuffe@gmail.com

Hi Andy,
It sounds like I'll have to reluctantly accept the problem might be the
tube, but take a look at the HV multiplier area first.
In the GDM-F520 Service Manual (page 3-5) is a diagram showing the "FBT"
with two knobs marked "Focus 1" & "Focus 2". Is that one each for Horizontal
& Vertical focus? If so , I wouldn't mind betting that the pot track contact
is playing up. If not, are there pots elsewhere?
I'm really keen to keep this monitor running for a few year, not just to get
my monies worth (important), but because I doubt I'll replace it with
anything as good! It's only thanks to everyone changing over to panel
screens that the opportunity to own a top of the range monitor like this has
come my way.Thank you progress! It's ironic that it turns out the top of the
range monitor has serious design flaws! Sony! Hang your heads in shame! Dig
out your Samurai Swords, or apologise and do your best to remedy the
situation (with information if nothing else)!
Scrim

 

[Dave]

"Dave" <dspear99ca@yahoo.delete.com> wrote in message
news:%CVTf.6013$J43.2877@edtnps90...

I've identified a bad transistor in the power supply of an audio
component,
circa 1981.

Well I went with a TIP42C, over-rated (6A vs. the 0.8A I am replacing AND
that's probably over-engineered) but available locally. I don't have any
mica insulators or plastic screws and they are an hour drive (or $15
shipping) away.

Thanks for everyone's help, I learned a great deal. BTW, I threw the new
PNP into my DMM's transistor testor and it came up with an hFE of 390. I am
thinking that this is a fairly useless number other than to show that the
transistor is functional as the hFE measurement will vary greatly with input
current. Wonder what the old one would weigh in at? Interestingly checking
the old transistor with a multimeter showed perfectly normal behavior, B-E
conducted one way only, B-C conducted one way only, C-E did not conduct.
But it didn't work in my transistor tester, came up 000 for hFE.

Again, thanks for the assistance.

Dave

 

[GregS]

In article <d%AUf.955$B_1.194@edtnps89>, "Dave" <dspear99ca@yahoo.delete.com> wrote:

"Dave" <dspear99ca@yahoo.delete.com> wrote in message
news:%CVTf.6013$J43.2877@edtnps90...
I've identified a bad transistor in the power supply of an audio
component,
circa 1981.

Well I went with a TIP42C, over-rated (6A vs. the 0.8A I am replacing AND
that's probably over-engineered) but available locally. I don't have any
mica insulators or plastic screws and they are an hour drive (or $15
shipping) away.

I still don't know where you got that spec. What was the manufacturer of that
obsolete unit.

Thanks for everyone's help, I learned a great deal. BTW, I threw the new
PNP into my DMM's transistor testor and it came up with an hFE of 390. I am
thinking that this is a fairly useless number other than to show that the
transistor is functional as the hFE measurement will vary greatly with input
current. Wonder what the old one would weigh in at? Interestingly checking
the old transistor with a multimeter showed perfectly normal behavior, B-E
conducted one way only, B-C conducted one way only, C-E did not conduct.
But it didn't work in my transistor tester, came up 000 for hFE.

Again, thanks for the assistance.

You really need sets of curves to get a real indication of things.
I have mostly tested them out with an analog ohmeter, my favorite.
Sometimes you will see extra leakage on CE or other terminals
when they are bad. I have not tested a bad unit with the diode
test function, which should indicate some voltage drop across CE.
greg

 

[Glen in Orlando]

Dave wrote:

"Glen in Orlando" <nospam.for.me@spamfree.com> wrote in message
news:442189DC.6000708@spamfree.com...

We have original 2SB527 in stock for US$1.99 each.

http://www.acme-sales.net


Holy sh#t, this site is a GOLDMINE! You sell transistors that haven't been
made since 1975! Tons of them!

Thanks, it's in my bookmark file. I already bought a TIP42C (over-rated,
but at $1.99 the price was right) at my local electronics store. BTW, how
much is shipping to Canada?

Glad you like it, Dave! We carry a lot of "new old stock"
items, as well as the "latest and greatest."

Shipping to Canada is the same as anywhere else, and
shows up in the shopping cart as you add items. (BTW we ship
to Canada every day).

Orders over US$50.00 - FREE shipping and handling
Orders US$20.01 to US$50.00 - S & H = US$6.99
Orders US$10.00 to US$20.00 - S & H = US$8.49
Orders unders US$10.00 - S & H = US$11.99

For orders under US$50.00 a small additional charge
will be added for flybacks.

Typically we use US Postal Service Global Priority Mail
to Canada, which arrives in about 4-7 days.

If you need more information please call us toll-free at
1-800-575-9833 (USA and Canada) or 1-407-296-2333.

Glen Goodwin
ACME Enterprises of Orlando
http://www.acme-sales.net

 

[Andy Cuffe]

On Thu, 23 Mar 2006 14:56:32 GMT, "Scrim" <nospam@nospam.com> wrote:

In the GDM-F520 Service Manual (page 3-5) is a diagram showing the "FBT"
with two knobs marked "Focus 1" & "Focus 2". Is that one each for Horizontal
& Vertical focus? If so , I wouldn't mind betting that the pot track contact
is playing up. If not, are there pots elsewhere?
I'm really keen to keep this monitor running for a few year, not just to get
my monies worth (important), but because I doubt I'll replace it with
anything as good! It's only thanks to everyone changing over to panel
screens that the opportunity to own a top of the range monitor like this has
come my way.Thank you progress! It's ironic that it turns out the top of the
range monitor has serious design flaws! Sony! Hang your heads in shame! Dig
out your Samurai Swords, or apologise and do your best to remedy the
situation (with information if nothing else)!
Scrim

Yes, those are the horizontal and vertical focus knobs. One affects
both almost equally and the other mostly affects the horizontal. It's
worth running both controls through their entire adjustment range a
few times just in case it is a dirty pot or something.

Display a pattern of white vertical lines and adjust the horizontal
for the thinnest vertical lines. Don't forget to look at the extreme
right and left edges because a small misadjustment can make the edges
extremely blurry. The correct setting will be a compromise between
the edges and center. Next display some thin horizontal lines and
adjust the vertical focus for the thinnest horizontal lines. Also be
sure the check the top and bottom focus as well as the center. Go
between them a few times and finish on the vertical focus so the
raster lines are as sharp as possible. That's not the official
adjustment procedure, but I've found it produces the best results.

These are very nice monitors, but they have their share of problems.
The other common problem is that the brightness tends to increase as
the CRT ages. Eventually it gets so bright that it can't produce
black at all. The official fix is to use the alignment software to do
a complete grayscale adjustment. This requires software and
equipment not available to most people. There is a resistor that can
be changed to reduce the G2 voltage. Later models could correct this
problem using the color return feature, but I don't think the F520
can.
Andy Cuffe

acuffe@gmail.com

 

[Dave]

"GregS" <szekeres@pitt.edu> wrote in message
news:dvumv5$fg7$1@usenet01.srv.cis.pitt.edu...

In article <d%AUf.955$B_1.194@edtnps89>, "Dave"
dspear99ca@yahoo.delete.com> wrote:

"Dave" <dspear99ca@yahoo.delete.com> wrote in message
news:%CVTf.6013$J43.2877@edtnps90...
I've identified a bad transistor in the power supply of an audio
component,
circa 1981.

Well I went with a TIP42C, over-rated (6A vs. the 0.8A I am replacing AND
that's probably over-engineered) but available locally. I don't have any
mica insulators or plastic screws and they are an hour drive (or $15
shipping) away.

I still don't know where you got that spec. What was the manufacturer of
that
obsolete unit.

http://www.geocities.com/saphanlex/p/tr.htm

http://www.datasheets.org.uk/specsheet.php?part=2SB527
http://www.datasheets.org.uk/databooks/databook.php?q=100
translated directly from Japanese:
http://translate.google.com/translate?hl=en&sl=ja&u=http://homepage3.nifty.com/ebina2540/data/2SB/2SB0501-0600.htm&prev=/search%3Fq%3D2sb527%2Brating%26hl%3Den%26hs%3DQfp%26lr%3D%26client%3Dfirefox-a%26rls%3Dorg.mozilla:en-USfficial

I'll have a look at the part and get the manufacturer.

Thanks for everyone's help, I learned a great deal. BTW, I threw the new
PNP into my DMM's transistor testor and it came up with an hFE of 390. I
am
thinking that this is a fairly useless number other than to show that the
transistor is functional as the hFE measurement will vary greatly with
input
current. Wonder what the old one would weigh in at? Interestingly
checking
the old transistor with a multimeter showed perfectly normal behavior,
B-E
conducted one way only, B-C conducted one way only, C-E did not conduct.
But it didn't work in my transistor tester, came up 000 for hFE.

Again, thanks for the assistance.

You really need sets of curves to get a real indication of things.
I have mostly tested them out with an analog ohmeter, my favorite.
Sometimes you will see extra leakage on CE or other terminals
when they are bad. I have not tested a bad unit with the diode
test function, which should indicate some voltage drop across CE.
greg

 

[GregS]

In article <0kDUf.1295$B_1.651@edtnps89>, "Dave" <dspear99ca@yahoo.delete.com> wrote:

"GregS" <szekeres@pitt.edu> wrote in message
news:dvumv5$fg7$1@usenet01.srv.cis.pitt.edu...
In article <d%AUf.955$B_1.194@edtnps89>, "Dave"
dspear99ca@yahoo.delete.com> wrote:

"Dave" <dspear99ca@yahoo.delete.com> wrote in message
news:%CVTf.6013$J43.2877@edtnps90...
I've identified a bad transistor in the power supply of an audio
component,
circa 1981.

Well I went with a TIP42C, over-rated (6A vs. the 0.8A I am replacing AND
that's probably over-engineered) but available locally. I don't have any
mica insulators or plastic screws and they are an hour drive (or $15
shipping) away.

I still don't know where you got that spec. What was the manufacturer of
that
obsolete unit.

http://www.geocities.com/saphanlex/p/tr.htm
http://www.datasheets.org.uk/specsheet.php?part=2SB527
http://www.datasheets.org.uk/databooks/databook.php?q=100
translated directly from Japanese:
http://translate.google.com/translate?hl=en&sl=ja&u=http://homepage3.nifty.com/
ebina2540/data/2SB/2SB0501-0600.htm&prev=/search%3Fq%3D2sb527%2Brating%26hl%3De
n%26hs%3DQfp%26lr%3D%26client%3Dfirefox-a%26rls%3Dorg.mozilla:en-USfficial

I'll have a look at the part and get the manufacturer.

Taken from my Towers 1980 edition databook, the main
difference is the packge type, clearly a TO126 as
the replacement shows2sb631
http://www.ortodoxism.ro/datasheets/sanyo/ds_pdf_e/2SB631K.pdf
The max current spec does vary among the bunch.

I have about 8 different replacement numbers as I have gone through all this.

greg

Thanks for everyone's help, I learned a great deal. BTW, I threw the new
PNP into my DMM's transistor testor and it came up with an hFE of 390. I
am
thinking that this is a fairly useless number other than to show that the
transistor is functional as the hFE measurement will vary greatly with
input
current. Wonder what the old one would weigh in at? Interestingly
checking
the old transistor with a multimeter showed perfectly normal behavior,
B-E
conducted one way only, B-C conducted one way only, C-E did not conduct.
But it didn't work in my transistor tester, came up 000 for hFE.

Again, thanks for the assistance.

You really need sets of curves to get a real indication of things.
I have mostly tested them out with an analog ohmeter, my favorite.
Sometimes you will see extra leakage on CE or other terminals
when they are bad. I have not tested a bad unit with the diode
test function, which should indicate some voltage drop across CE.
greg

 

[Scrim]

"Andy Cuffe" <acuffe@gmail.com> wrote in message
news:1hr522dfh2djaa14lnf27ake6l8rgo909c@4ax.com...

On Thu, 23 Mar 2006 14:56:32 GMT, "Scrim" <nospam@nospam.com> wrote:

In the GDM-F520 Service Manual (page 3-5) is a diagram showing the "FBT"
with two knobs marked "Focus 1" & "Focus 2". Is that one each for
Horizontal
& Vertical focus? If so , I wouldn't mind betting that the pot track
contact
is playing up. If not, are there pots elsewhere?
I'm really keen to keep this monitor running for a few year, not just to
get
my monies worth (important), but because I doubt I'll replace it with
anything as good! It's only thanks to everyone changing over to panel
screens that the opportunity to own a top of the range monitor like this
has
come my way.Thank you progress! It's ironic that it turns out the top of
the
range monitor has serious design flaws! Sony! Hang your heads in shame!
Dig
out your Samurai Swords, or apologise and do your best to remedy the
situation (with information if nothing else)!
Scrim



Yes, those are the horizontal and vertical focus knobs. One affects
both almost equally and the other mostly affects the horizontal. It's
worth running both controls through their entire adjustment range a
few times just in case it is a dirty pot or something.

Display a pattern of white vertical lines and adjust the horizontal
for the thinnest vertical lines. Don't forget to look at the extreme
right and left edges because a small misadjustment can make the edges
extremely blurry. The correct setting will be a compromise between
the edges and center. Next display some thin horizontal lines and
adjust the vertical focus for the thinnest horizontal lines. Also be
sure the check the top and bottom focus as well as the center. Go
between them a few times and finish on the vertical focus so the
raster lines are as sharp as possible. That's not the official
adjustment procedure, but I've found it produces the best results.

These are very nice monitors, but they have their share of problems.
The other common problem is that the brightness tends to increase as
the CRT ages. Eventually it gets so bright that it can't produce
black at all. The official fix is to use the alignment software to do
a complete grayscale adjustment. This requires software and
equipment not available to most people. There is a resistor that can
be changed to reduce the G2 voltage. Later models could correct this
problem using the color return feature, but I don't think the F520
can.
Andy Cuffe

acuffe@gmail.com

Thanks Andy, that's very helpful.
My F520 has "Image Restoration", which I think must be the "color return
feature" you describe?
The User Manual has this to say about it:
-----------------------------
To restore the color from the EASY, PRESET, or sRGB modes ( IMAGE
RESTORATION):
You can restore the color to the original factory quality levels. Before
using this feature, the monitor must have been in normal operation mode
(green power indicator on) for at least 30 minutes. You may need to adjust
your computer's power saving settings. If the monitor has not been on for at
least 30 minutes, the "AVAILABLE AFTER WARM UP" message will appear. Also,
this function may gradually lose its effectiveness due to the natural aging
of the Trinitron picture tube.
-----------------------------
Scrim

 

Dave wrote:

I recently picked up a Sansui T-80 tuner (circa 1981)... it's got some flaky
performance, sometimes good, sometimes not so good. I'm going to replace
all of the ancient electrolytic caps but there is one I cannot source:

0.15uF 100V polar electrolytic

Not being so wise in the ways of electronic componentry and being perplexed
by all of the different variants of capacitors in particular, can I use a
non-electrolytic in this app? Say, a metallized polyester or polypropylene
film? They appear to have tighter specs (+/-5% vs. +/-20%) than comparable
electrolytics. These particular caps are coupling caps on the outputs of
the MPX decoder chips in series with the output jacks of the tuner... the
last cap the signal goes through. What are the ramifications of using a
0.1uF or a 0.22uF cap (both available from DigiKey) in this application?

I'm also having a tough time finding some electrolytic caps for an
amplifier:

0.47uF 50V, +75/-10% tolerance
22uF 16V, +50/-10% tolerance
47uF 25V, +50/-10% tolerance
100uF 25V, +50/-10% tolerance

Any advice greatly appreciated.

Dave

Having also read your subsequent posts in this thread:

At http://www.mouser.com , you can find some nice metallized polyester
caps by AVX, such as the 0.15 uF 63V 10% for $0.08, qty 1 (or 5% for
$0.18). They are SMALL, too: 2.5mm D x 7.5mm W x 6.5mm H, with
0.2-inch lead spacing. They go up to 2.2uF, although the size at 2.2uF
rises to 6mm D x 7.5mm W x 12mm H.

The Mouser.com part number for the 0.15 uF 10% one is 581-BQ014D0154K.
The 5% version's part number is the same, except for a J instead of K,
at the end.

The 0.47uF 63V 5% and 10% metallized polyester AVX caps in the same
series have Mouser.com part numbers 581-BQ074D047J and ...K, and go for
$0.25 and $0.23, qty 1.

For the 0.15uF cap, I would tend to prefer the WIMA MKP2-series
metallized polypropylene, especially if small size is important: The
Mouser.com part number 505-MKP20.15/100/5 is rated 100vdc/63vac, 5%,
and sells for $0.87 for qty 1. It's SMALL, too, at 7.2mm D x 7.2mm W x
13mm H, with 5mm lead spacing.

If you can tolerate a slightly-larger size, you can get some metallized
polypropylene caps with "< 0.1% dissipation factor (DF)": Mouser.com
part number 1429-1474 is 0.47uF 100v 10%, for %0.70 qty 1, and measures
10mm D x 18.5mm W x 15.5mm H. And there's also the 1429-2475, 4.7uF
250v 10% for $3.49 qty 1, measuring 37mm W x 18mm D x 27mm H.
And once you get up to sizes that large, there are quite a few
alternatives available, in film caps.

There are film caps in the larger capacitance values, at Mouser.com,
too, although they tend to get a bit pricey, in most cases. For
example, check out the ones in the AVX "FFB" series (which seem to be
intended for DC filtering).

Note that you may have to solder wires onto the leads, if you are
replacing physically-larger caps with some of the very small ones that
I mentioned above.

Regarding whether you can always replace electrolytics with
similarly-rated film caps (and then get better performance and
reliability), the answer might be "usually". But note that, sometimes,
maybe especially in power-supply bypass/decoupling applications near
ICs (or, e.g., similarly, on a per-board basis), the designer might
have relied on the higher ESR (equivalent series resistance) of an
el-cheapo electrolytic (or a tantalum) cap to be a necessary part of
the circuit (maybe, e.g., for damping). If I ever had to guess, then I
would guess that, for an audio signal path cap, a film cap would almost
always be better than an electrolytic (and I would then almost always
prefer polypropylene over polyester).

Sorry for the long post. Gotta run. Have fun.

Tom

 

[Andy Cuffe]

On Thu, 23 Mar 2006 23:14:20 GMT, "Scrim" <nospam@nospam.com> wrote:

Thanks Andy, that's very helpful.
My F520 has "Image Restoration", which I think must be the "color return
feature" you describe?

That's the feature I'm thinking of, but for some reason it doesn't
work (well) on a lot of the 21" monitors. For some reason it works
fine on the same age 19" monitors. They fixed it on the later 21",
bit I think the F520 was made before they fixed it.

If it works it really will restore the correct brightness and
grayscale. I've seen monitors that were so far out of adjustment that
they were scrapped. Simply running the image restore made them look
like new.
Andy Cuffe

acuffe@gmail.com

 

[PE1E]

Thanks, sck0006.
I'll check on this one.
The flaw occurred during transport from US to EU.
Maybe the UPS carrier people weren't aware this old lady had te be
treated with care...

Peter, PE1E
Amsterdam.

 

[PE1E]

Jorgen,

Thanks.
I will subscribe to that group.
There, I found already that the lamp behind de rotary dial could be
gone.
Thanks,

Peter, PE1E
Amsterdam.

 

[Sam Goldwasser]

Jim Yanik <jyanik@abuse.gov> writes:

Sam Goldwasser <sam@saul.cis.upenn.edu> wrote in
news:6wzmjo306e.fsf@saul.cis.upenn.edu:

Jim Yanik <jyanik@abuse.gov> writes:

"Ancient_Hacker" <grg2@comcast.net> wrote in
news:1142617094.382451.289320@j52g2000cwj.googlegroups.com:

Oh, there's also a big voltage divider resistor (the white ceramic
thing) Any moisture, dust, or leakage there and you tend to get
unstable HV.



The HV thick-film resistor network(TEK-made) has the HV feedback for
regulation on one side,and the CRT focus divider on the other. Either
one can go out-of-tolerance,and the metal pins can crack and be
intermittent.I've never been successful in resoldering them,either.

I do not think this part would be the cause of his intensity
modulation.

It may be.

New followup: I've now got the thing open. Since it appeared heat dependent,
I used a rubber tube to blow on various components in the HV area.
Blowing on the thick film resistor network even immeidately after
power-on and the beam appeared (already messed up) seemed to make a
big difference causing the symptoms to disappear entirely for awhile.
This could not have been heat related because it was within 10 seconds of
powering up so nothing really could get hot. Then, after touching the
thick film assembly perhaps with a few wiggles thrown in, the problem
has disappeared entirely and has not reappeared. I've since cleaned
it with alcohol and I will be running the scope off and on for a few
hours over the next few days on the bench to see what happens.

Of course, the instant I put the cover back on and replace the scope in its
hard-to-reach spot, it will screw up again.

So the working hypothesis is that indeed either contamination or cracked
joints to this part.

If cracked joints turns out to be confirmed with the problem reappearing,
I would probably try conductive silver Epoxy first at each of the
connections to the thick film itself rather than solder. If that
didn't last, then what about fashioning a replacement from discrete parts?
It might be a bit of a challenge to get high voltage resistors to fit in
the space but seems like it could work. It's only 4 resistors, though
admittedly 3 of them are high resistance (6.57M, 25.6M, 24.5M, and 550K)
and at least 2 of them need to withstand almost 3 kV.

Any comments?

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

 

[n cook]

Sam Goldwasser <sam@saul.cis.upenn.edu> wrote in message
news:6w7j6hds7c.fsf@saul.cis.upenn.edu...

Jim Yanik <jyanik@abuse.gov> writes:

Sam Goldwasser <sam@saul.cis.upenn.edu> wrote in
news:6wzmjo306e.fsf@saul.cis.upenn.edu:

Jim Yanik <jyanik@abuse.gov> writes:

"Ancient_Hacker" <grg2@comcast.net> wrote in
news:1142617094.382451.289320@j52g2000cwj.googlegroups.com:

Oh, there's also a big voltage divider resistor (the white ceramic
thing) Any moisture, dust, or leakage there and you tend to get
unstable HV.



The HV thick-film resistor network(TEK-made) has the HV feedback for
regulation on one side,and the CRT focus divider on the other. Either
one can go out-of-tolerance,and the metal pins can crack and be
intermittent.I've never been successful in resoldering them,either.

I do not think this part would be the cause of his intensity
modulation.

It may be.

New followup: I've now got the thing open. Since it appeared heat
dependent,
I used a rubber tube to blow on various components in the HV area.
Blowing on the thick film resistor network even immeidately after
power-on and the beam appeared (already messed up) seemed to make a
big difference causing the symptoms to disappear entirely for awhile.
This could not have been heat related because it was within 10 seconds of
powering up so nothing really could get hot. Then, after touching the
thick film assembly perhaps with a few wiggles thrown in, the problem
has disappeared entirely and has not reappeared. I've since cleaned
it with alcohol and I will be running the scope off and on for a few
hours over the next few days on the bench to see what happens.

Of course, the instant I put the cover back on and replace the scope in
its
hard-to-reach spot, it will screw up again.

So the working hypothesis is that indeed either contamination or cracked
joints to this part.

If cracked joints turns out to be confirmed with the problem reappearing,
I would probably try conductive silver Epoxy first at each of the
connections to the thick film itself rather than solder. If that
didn't last, then what about fashioning a replacement from discrete parts?
It might be a bit of a challenge to get high voltage resistors to fit in
the space but seems like it could work. It's only 4 resistors, though
admittedly 3 of them are high resistance (6.57M, 25.6M, 24.5M, and 550K)
and at least 2 of them need to withstand almost 3 kV.

Any comments?

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
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Some woven glass sleeving , cut to required lengths and formed into a
compressable and insulated pad or more pads if you cannot localise better
and cautiosly compressed by cable tie/s around the thick film ?
I've only done similar on low V SM ICs that are covered in black epoxy ,
boards as well, so impossible to re-do the SM solder , to the ceramic
boards, and is a throw away job otherwise.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

 

[Jim Yanik]

Sam Goldwasser <sam@saul.cis.upenn.edu> wrote in
news:6w7j6hds7c.fsf@saul.cis.upenn.edu:

Jim Yanik <jyanik@abuse.gov> writes:

Sam Goldwasser <sam@saul.cis.upenn.edu> wrote in
news:6wzmjo306e.fsf@saul.cis.upenn.edu:

Jim Yanik <jyanik@abuse.gov> writes:

"Ancient_Hacker" <grg2@comcast.net> wrote in
news:1142617094.382451.289320@j52g2000cwj.googlegroups.com:

Oh, there's also a big voltage divider resistor (the white
ceramic thing) Any moisture, dust, or leakage there and you
tend to get unstable HV.



The HV thick-film resistor network(TEK-made) has the HV feedback
for regulation on one side,and the CRT focus divider on the other.
Either one can go out-of-tolerance,and the metal pins can crack
and be intermittent.I've never been successful in resoldering
them,either.

I do not think this part would be the cause of his intensity
modulation.

It may be.

New followup: I've now got the thing open. Since it appeared heat
dependent, I used a rubber tube to blow on various components in the
HV area. Blowing on the thick film resistor network even immeidately
after power-on and the beam appeared (already messed up) seemed to
make a big difference causing the symptoms to disappear entirely for
awhile. This could not have been heat related because it was within 10
seconds of powering up so nothing really could get hot. Then, after
touching the thick film assembly perhaps with a few wiggles thrown in,
the problem has disappeared entirely and has not reappeared. I've
since cleaned it with alcohol and I will be running the scope off and
on for a few hours over the next few days on the bench to see what
happens.

Of course, the instant I put the cover back on and replace the scope
in its hard-to-reach spot, it will screw up again.

So the working hypothesis is that indeed either contamination or
cracked joints to this part.

If cracked joints turns out to be confirmed with the problem
reappearing, I would probably try conductive silver Epoxy first at
each of the connections to the thick film itself rather than solder.
If that didn't last, then what about fashioning a replacement from
discrete parts? It might be a bit of a challenge to get high voltage
resistors to fit in the space but seems like it could work. It's only
4 resistors, though admittedly 3 of them are high resistance (6.57M,
25.6M, 24.5M, and 550K) and at least 2 of them need to withstand
almost 3 kV.

Any comments?

I've wondered if low melting point solder like what comes in the ChipQuik
desoldering kit might work on thick-film connections.It wasn't available to
me at Tek.The conductive silver epoxy may be a better idea. Trouble if you
have to resolder the thick-film back into the motherboard.

Alternately,you could fashion a small PCB to fit where the thick film
goes,and solder your resistors to the PCB. I've not tried this,though.

--
Jim Yanik
jyanik
at
kua.net

 

[Sam Goldwasser]

Jim Yanik <jyanik@abuse.gov> writes:

Sam Goldwasser <sam@saul.cis.upenn.edu> wrote in
news:6w7j6hds7c.fsf@saul.cis.upenn.edu:

Jim Yanik <jyanik@abuse.gov> writes:

Sam Goldwasser <sam@saul.cis.upenn.edu> wrote in
news:6wzmjo306e.fsf@saul.cis.upenn.edu:

Jim Yanik <jyanik@abuse.gov> writes:

"Ancient_Hacker" <grg2@comcast.net> wrote in
news:1142617094.382451.289320@j52g2000cwj.googlegroups.com:

Oh, there's also a big voltage divider resistor (the white
ceramic thing) Any moisture, dust, or leakage there and you
tend to get unstable HV.



The HV thick-film resistor network(TEK-made) has the HV feedback
for regulation on one side,and the CRT focus divider on the other.
Either one can go out-of-tolerance,and the metal pins can crack
and be intermittent.I've never been successful in resoldering
them,either.

I do not think this part would be the cause of his intensity
modulation.

It may be.

New followup: I've now got the thing open. Since it appeared heat
dependent, I used a rubber tube to blow on various components in the
HV area. Blowing on the thick film resistor network even immeidately
after power-on and the beam appeared (already messed up) seemed to
make a big difference causing the symptoms to disappear entirely for
awhile. This could not have been heat related because it was within 10
seconds of powering up so nothing really could get hot. Then, after
touching the thick film assembly perhaps with a few wiggles thrown in,
the problem has disappeared entirely and has not reappeared. I've
since cleaned it with alcohol and I will be running the scope off and
on for a few hours over the next few days on the bench to see what
happens.

Of course, the instant I put the cover back on and replace the scope
in its hard-to-reach spot, it will screw up again.

So the working hypothesis is that indeed either contamination or
cracked joints to this part.

If cracked joints turns out to be confirmed with the problem
reappearing, I would probably try conductive silver Epoxy first at
each of the connections to the thick film itself rather than solder.
If that didn't last, then what about fashioning a replacement from
discrete parts? It might be a bit of a challenge to get high voltage
resistors to fit in the space but seems like it could work. It's only
4 resistors, though admittedly 3 of them are high resistance (6.57M,
25.6M, 24.5M, and 550K) and at least 2 of them need to withstand
almost 3 kV.

Any comments?

I've wondered if low melting point solder like what comes in the ChipQuik
desoldering kit might work on thick-film connections.It wasn't available to
me at Tek.The conductive silver epoxy may be a better idea. Trouble if you
have to resolder the thick-film back into the motherboard.

I don't know but I have both indium solder (93C) and that ChipQuik stuff.
However, if I can identify one cracked joint, the silver Epoxy should take
care of it.

I have no intention of removing the hybrid from the mainboard! Silver
Epoxy on those joints as well if need be.

Alternately,you could fashion a small PCB to fit where the thick film
goes,and solder your resistors to the PCB. I've not tried this,though.

So far the cleaning is holding up. Fingers crossed.

Thanks.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

 

[JW]

On 26 Mar 2006 12:35:51 -0500 Sam Goldwasser <sam@saul.cis.upenn.edu>
wrote in Message id: <6w7j6hds7c.fsf@saul.cis.upenn.edu>:

I used a rubber tube to blow on various components in the HV area.

OK, I'm assuming you've found a way to heat the air first. I'm interested
in this setup - could you elaborate?

 

[Sam Goldwasser]

JW <none@dev.nul> writes:

On 26 Mar 2006 12:35:51 -0500 Sam Goldwasser <sam@saul.cis.upenn.edu
wrote in Message id: <6w7j6hds7c.fsf@saul.cis.upenn.edu>:

I used a rubber tube to blow on various components in the HV area.

OK, I'm assuming you've found a way to heat the air first. I'm interested
in this setup - could you elaborate?

In this case, it wasn't a matter of heat. It turned out that simply air flow
made the difference since this occurred immediately after power on before anything
had a chance to heat up.

If I had to provide heat, a blow dryer would have been my tool of
choice

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

 

[Jim Yanik]

Sam Goldwasser <sam@saul.cis.upenn.edu> wrote in
news:6wr74nsntn.fsf@saul.cis.upenn.edu:

JW <none@dev.nul> writes:

On 26 Mar 2006 12:35:51 -0500 Sam Goldwasser <sam@saul.cis.upenn.edu
wrote in Message id: <6w7j6hds7c.fsf@saul.cis.upenn.edu>:

I used a rubber tube to blow on various components in the HV area.

OK, I'm assuming you've found a way to heat the air first. I'm
interested in this setup - could you elaborate?

In this case, it wasn't a matter of heat. It turned out that simply
air flow made the difference since this occurred immediately after
power on before anything had a chance to heat up.

If I had to provide heat, a blow dryer would have been my tool of
choice

Note that your breath will have high levels of moisture in it,that could
alter the conductivity of the thick-film elements,especially if the thick-
film is dirty.

I used to use an ordinary hairdryer(folding travel style) at low heat,until
one of the cleaning people stole it.(along with my TI-30 calculator)

a paper cone narrowed the air flow to what I desired.

--
Jim Yanik
jyanik
at
kua.net