Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Coolant leak, Sony 43T90

Thought we had this one licked but it failed.

Clean the living crap out of it, pour solvent all over the board and
it failed. This is the signal board, I found the leak. The red focus
was off so at the estimate stage I said "CRT socket". Wouldn't be the
first time, but in this case so much coolant had leaked the chamber
was only half full. The optical focus was off due to that.

There was actually a convergence problem masked by this condition. I
found it anyway, changed the O ring and cover plate of the CRT and
refilled it, making sure the bellows was collapsed.

Another symptom was the volume going up despite it's setting, I saw
the corrosion on the board and it was pretty much time to clean it. It
failed the next day and has again darkened my bench.

It had intermittent H drive, the six flashes of the standby light
means HSTOP, and as I got the print out and figured out where to hang
the scope probe, it started working.

Well I decided to clean the board more and actually found somemore
coolant under it, but not where I would expect. It was at the back of
the chassis. The way I figure it is that there is so much coolant
soaked into this board we could never get it all out.

When it fired up finally it had no color. Now, I have soaked this
thing pretty good with acetone, and at this point I am wondering about
the integrity of the cases of electronic components.

What I am wondering is if between the coolant and acetone there could
be damage either to the color as well as the 503K crystal, or if I
should change the jungle IC. Once the IC is out of there of course I
intend to give the PCB another cleaning.

But now there is another twist. The second time I cleaned it I
resoldered it, not that the connections were bad, but I was figuring
that this being a multiple layer board the coolant might be soaked
into it. I figured the heat would make it boil out.

Now it has stopped responding to the remote. That is a small issue
other than what I got when it comes to sweep and chroma. There is only
so much it can be.

There is a possibility I need a better technique to deal with coolant
on PCBs, what do you all do ? I do have a fairly decent success rate,
but I think this one is really soaked.

I am pretty sure this has been mentioned before, but it might be time
for another round, because anybody in the bigscreen business has more
experience with it, I can almost be sure.

Thanks for whatever you got.

JURB

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AJ AJ is offline
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Default Coolant leak, Sony 43T90

Seen way too many pcbs damaged by the coolant leakage. Sorry part is it is
almost impossible to get all of the crap out of the board, out from under
through hole mounted components, and/or soaked into the actual board
substrate. Normally we just tell the customer the set is not repairable, or
try to get a board out of a rebuilder like PTS. Had a few Hitachi sets that
leaked so badly that they damaged customer's carpet benieth the set.
Suggested the customer contact Hitachi directly to see if any help for
carpet repair-replacment would be realized.
We have a few techs that have attempted soaking the pcbs in distilled water
and then allowing them to air dry for a couple of weeks before even
attempting to diagnose failures. Problem is the additional time in trying to
get the item back into service for the customers, then you don't know if the
thing will fail in the near future. Almost as bad as trying ot repair a set
that has sustained a direct lightning hit, the hidden faults will chase you
around and around. Good luck.
wrote in message
oups.com...
Thought we had this one licked but it failed.

Clean the living crap out of it, pour solvent all over the board and
it failed. This is the signal board, I found the leak. The red focus
was off so at the estimate stage I said "CRT socket". Wouldn't be the
first time, but in this case so much coolant had leaked the chamber
was only half full. The optical focus was off due to that.

There was actually a convergence problem masked by this condition. I
found it anyway, changed the O ring and cover plate of the CRT and
refilled it, making sure the bellows was collapsed.

Another symptom was the volume going up despite it's setting, I saw
the corrosion on the board and it was pretty much time to clean it. It
failed the next day and has again darkened my bench.

It had intermittent H drive, the six flashes of the standby light
means HSTOP, and as I got the print out and figured out where to hang
the scope probe, it started working.

Well I decided to clean the board more and actually found somemore
coolant under it, but not where I would expect. It was at the back of
the chassis. The way I figure it is that there is so much coolant
soaked into this board we could never get it all out.

When it fired up finally it had no color. Now, I have soaked this
thing pretty good with acetone, and at this point I am wondering about
the integrity of the cases of electronic components.

What I am wondering is if between the coolant and acetone there could
be damage either to the color as well as the 503K crystal, or if I
should change the jungle IC. Once the IC is out of there of course I
intend to give the PCB another cleaning.

But now there is another twist. The second time I cleaned it I
resoldered it, not that the connections were bad, but I was figuring
that this being a multiple layer board the coolant might be soaked
into it. I figured the heat would make it boil out.

Now it has stopped responding to the remote. That is a small issue
other than what I got when it comes to sweep and chroma. There is only
so much it can be.

There is a possibility I need a better technique to deal with coolant
on PCBs, what do you all do ? I do have a fairly decent success rate,
but I think this one is really soaked.

I am pretty sure this has been mentioned before, but it might be time
for another round, because anybody in the bigscreen business has more
experience with it, I can almost be sure.

Thanks for whatever you got.

JURB


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Default Coolant leak, Sony 43T90

Thanks for that,,,,,, discouragement. Actually it is not all
discourgement. Soaking in distilled water, especially if that water is
somehow agitated. Another idea would be to cycle it thermally.

I don't think anything in the way of solvents is safe enough to soak
the PCB for days or whatever, but distilled water might be a good
choice, especially since it is cheaper than alcohol or acetone.
Acetone can't be left on the board for long.

Perhaps the tank could be designed to hold the board in the water, or
some solution we might concoct, while keeping most of the top board
components above the liquid level.

Thought is good to solve this problem, that is where the real money
comes in the TV business.

I wonder if it would be safe to use the coils like an ultrasonic
cleaner. I can see where it may damage something, namely to anything
that works on piezoelectric principles. They are actually mechanical
devices. This includes crystals and resonators, and I kinda think also
things like SAW filters. Possibly even bandpass devices.

And then what of the cores of coils and transformers, can they be
damaged ?

Would it be a good idea, for example, to remove the flyback ? The
horizontal scan transformer ! The tuners ?

I think before undertaking this all this must be considered, but
ultrasonic would greatly accelerate the process.

And I would really like to know what PTS or Tristate Module does when
they get this problem.

We really need a way to get the coolant to migrate out from under the
parts. I had one came back with an intermittent H drive problem. It
was blowing the HOT. I saw the drive waveform's level at the peaks get
intermittently suppressed. The cause was corrosion at the bottom of
the H drive transformer. This set had been recently serviced for a
coolant leak.

I think one of the most important things in servicing this problem
successfully has to do with cooking the set after the repair. I would
suggest a week or more if possible. The problem is you run out of
space in the shop no matter how much square footage you have. Problems
show up in time, and when the unit warms up. It would be best to have
it fail at the shop, rather than to deliver a unit which will have to
come back.

Thanks, and any more ideas out there ? I am all ears.
Orrrrrrrr, , , , ,whatever.

JURB


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Default Coolant leak, Sony 43T90


wrote:

Would it be a good idea, for example, to remove the flyback ? The
horizontal scan transformer ! The tuners ?

I think before undertaking this all this must be considered, but
ultrasonic would greatly accelerate the process.



I do a lot of coolant leaks (3 Mitsus this week), and IMO the only
reliable way is to totally clean the board with ammonia and soap. I
use a product called Parsons Sudsy Ammonia dilluted about 5 to 1. The
ammonia suggestion comes from RCA. I tried several experiments by
putting coolant on scrapped PCs, and trying different cleaners and
solvents by contact only, no wiping or blotting. The ammonia is the
only thing I tried that really disolves the coolant and leaves the
board totally dry.

I remove any and every component that can hold\trap water, such as
transformers, tightly wound inductors, flyback, tuner, and all dense
edge connectors from the board. I then spray the complete assy with
the ammonia mixture several times over a half hour or so, until the
entire board is bright and shiny. I then rinse the board thoroughly
with scalding hot water several times ( I don't use deionized or RO
water, just tap). If any of the connectors had coolant contamination,
I clean these in the same way and dry quickly so they won't rust. I
replace any obviously burned or damaged components, reassemble the
board and try it. If it's not working, repair as usual. Single sided
boards usually work first shot. Multi layer boards like Mitsus often
have feed through failures. Under a high power loop, they usually
look blackened or swollen. Sometimes the only way of finding an open
feedthrough on a multi layer board is with an ohmmeter.

Removing all these components from the board before cleaning is time
consuming, but IMO it's the fastest way in the end.

John

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