Advice on fixing a Hitachi 27" TV

[Jcchan]

I've got a Hitachi TN-78042 27" TV that was working just fine. Then a
couple of months ago I noticed that from a cold start the picture would be
great but would deteriorate as it warms up until all I see is snow. Audio
is fine. The time that it takes for the picture to become scrambled (using
tuner or other video inputs) varies from 10 minutes to a couple of hours
depending on how cold the TV is. Once the picture was scrambled, I tried
using cold spray on the individual components to see if it was a thermal
problem but this did not correct the picture (on any of the video inputs -
coax, rca, or s-video). Any ideas on what else I should look for ? Does
this sound like a problem worth fixing or should I just buy a new TV?
Thanks.

James

 

[Jerry G.]

You still didn't find the thermo sensitive part. Did you check the power
supply outputs with a DVM to see if they are in specs? You may have to wait
for the fault, and use a scope to check the various stages for proper
performance. You will require to purchase the service manual to go through
the set in details.

Since the fault is on all inputs, this leaves the input circuits, video
processing path, and synch circuits. Also, the power supply, and horizontal
output secondary voltage output supplies are involved here as well.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
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"Jcchan" <jcchan@telusplanet.net> wrote in message
news:7Rwxb.55524$oN2.22029@edtnps84...
I've got a Hitachi TN-78042 27" TV that was working just fine. Then a
couple of months ago I noticed that from a cold start the picture would be
great but would deteriorate as it warms up until all I see is snow. Audio
is fine. The time that it takes for the picture to become scrambled (using
tuner or other video inputs) varies from 10 minutes to a couple of hours
depending on how cold the TV is. Once the picture was scrambled, I tried
using cold spray on the individual components to see if it was a thermal
problem but this did not correct the picture (on any of the video inputs -
coax, rca, or s-video). Any ideas on what else I should look for ? Does
this sound like a problem worth fixing or should I just buy a new TV?
Thanks.

James

 

[James Sweet]

"Jcchan" <jcchan@telusplanet.net> wrote in message
news:7Rwxb.55524$oN2.22029@edtnps84...

I've got a Hitachi TN-78042 27" TV that was working just fine. Then a
couple of months ago I noticed that from a cold start the picture would be
great but would deteriorate as it warms up until all I see is snow. Audio
is fine. The time that it takes for the picture to become scrambled
(using
tuner or other video inputs) varies from 10 minutes to a couple of hours
depending on how cold the TV is. Once the picture was scrambled, I tried
using cold spray on the individual components to see if it was a thermal
problem but this did not correct the picture (on any of the video inputs -
coax, rca, or s-video). Any ideas on what else I should look for ? Does
this sound like a problem worth fixing or should I just buy a new TV?
Thanks.

James

Freeze spray sounds like a great start, fire it up with the back off, wait
for it to get snowy, then give sections of the board a quick squirt with the
spray and find the area that makes a difference. Check inside the IF can
too, I fixed a Sony that had a problem there.

 

[Asimov]

"James Sweet" bravely wrote to "All" (28 Nov 03 07:14:27)
--- on the heady topic of "Re: Advice on fixing a Hitachi 27" TV"

JS> Reply-To: "James Sweet" <jamessweet@hotmail.com>

JS> Freeze spray sounds like a great start, fire it up with the back off,

JS> wait for it to get snowy, then give sections of the board a quick
JS> squirt with the spray and find the area that makes a difference. Check
JS> inside the IF can too, I fixed a Sony that had a problem there.

I once fixed a Hitachi tv's tuner that had a similar symptom. Turned out
there was the tiniest little metal particle imbedded in the solder flux
which shorted across 2 pins of the smt Philips VCO ic. As the tv
interior warmed up the flux would soften and the metal shard would make
contact (you guessed it -- only happened with the case back on!!!). The
vco voltage went up and the tv was picking up dead air snow. I knew it
was thermal but it took a microscopic examination of the vco ic pins to
find that one.

.... I ran Doublespace on my monitor & get 2 more TV channels.