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.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 140
Default PTV745 from hell, and you might not believe this

This is another one for the books. I file this with the "adjust
vertical height to cure picture turning red" and in another Sony, "a
bad speaker can cause no high voltage".

It is indeed from hell. When it got assignned to me the symptom was no
sound and it would not switch video inputs. It would do pretty much
the same thing as one with the option set wrong in the service menu,
which I have seen before.

At first I said "piece of cake, just set the option byte". Hardy har
har.

Well, as I was getting into the service menu the set quit. I asked
"did it shutdown too ?", the answer was no. So I did my thing with the
scope, pickng up radiation, first from the standby transformer, and
then the main SMPS tansformers. I got a very low amplitude which shut
down very quickly. This led me to look for a short, and sure enough
the HOT was shorted, and it blew the replacement immediately. This is
the same one, I reworked the PC board to accept a PTV500 series
deflection output transformer. It requires about six or seven jumpers
to do this, and of course you have to grind foils out. The tough one
is the huge ground plane at the one corner. But I got it done and the
set is up and running, but the same symptom exists.

I have been all over the option code, in the service manual, set them
to defaults, all that. I had checked all the supplies, I had done
everything any sane and competent tech would do, except there is one
thing. But I want you, you competent techs in here to tell me
truthfully if you would have checked what turned out to be the
problem, which I will reveal momentarily.

I had three signal boards do the same thing. One was from the boneyard
and we actually bought one, figuring this is some sort of fluke and it
would not be the first time. We put a new board in it, well a PTS, and
it was the same !

Well I had checked all kinds of stuff on the original board, as well
as it's boneyard replacement. Until a certain point I had gotten
myself into a corner. The new board, I went through the options, it
was set right except for one A2 instead of B3, and that is the remote
locator, this was not the problem.

Finally I decide to go to IC1, the video switcher. This model has the
ghost cancellor connection, which obviously has tuner video. I
switched to video 1 and plugged in a cable to video 1. Actually I just
touched the contact, if I did video would disappear, but when just
touching the inner connector (without tripping the switch), I got
sync. Like that I scoped the IC, and found a few other things along
the way, the video output is actually switching. This SNAFU has to do
with the COMB filter and video switching.

Well, I decided to scope all the pins of IC 1, I downloaded a
datasheet and got busy. I just went through all of them.

Well eventually I got to the SDA and SCL pins. One was being clamped
to a 3V high. I got it by the balls now, but where ? Am I in a
situation where the convergence module is causing no sound ? Damn,
that would be for the books.

Being a bit bold, I disconnected the convergence plug from the small
signal board. This did not affect the convergence actually, apparently
it did need any data at the time. It was still plugged into the power/
deflection. I scoped SDA and SCL right there, and it was still no
good.

Thinking and thinking about it I was at a loss at the moment. But then
I noticed that SDA and SCL also go to the power/deflection board.
Why ?

I found out why, IC551 (TA8859 vertical correction IC) uses SDA and
SCL. That was the culprit.

So we have vertical height causing the picture to go red, an open
subwoofer causing total shutdown, STK 392-120s instead of 392-570s
causing high voltage arcing and now a vertical driver IC causing no
sound and no video switching.

And here's a couple of things to ponder, first of all the video
switcher IC was actually working. It was switching properly even with
the reduced amplitude. But something else wasn't.

I believe I have answered my own question though, this phenomenon has
something to do with the PIP. Because I did notice the lack of a PIP
window even in the customer menu, in PIP color and PIP tint. So that
is the culprit, when the options aren't right, the PIP circuit is the
one that REALLY requires the correct data.

While I was in the service menu I had no reason to go into the VSCORR
or the Vwhatever, which is what addreses that TA8859, so I did not
know that it was not working. Well I bet it wasn't addressable at the
time. I just changed it and the set works.

After the debacle with the sweep transformer, we are planning on a
celebratrion for it's leaving the shop. I am not the first tech to
work on it, but I think I might be the last. But it does produce a
good picture. Everybody happy now.

I told the boss, and I think this is true, if it would've clamped a
little higher, like at four volts, or if the PIP system would tolerate
it and work properly anyway, we might've never known about the
problem. It could've run for ten years that way.

Not a bad learning experience, but this chipset is on it's way out. It
came too late. Of course the principle applies to newer sets, but this
was just wierd.

Wanna buy a good PTV745 signal board ? We got two.

My next project is to use parts and or adapt one to a GR5 chassis.
I'll let you know how that goes.

JURB

Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
PTV 745 from hell [email protected] Electronics Repair 1 September 12th 07 05:51 PM
What the hell is this? I am I Home Repair 2 August 30th 05 02:04 AM
2x4 from hell! John DeBoo Woodworking 6 June 8th 05 11:56 PM
Ok why the hell did I buy this???? Waynemak Metalworking 18 June 5th 05 08:15 PM
What the Hell is it? JRJohnson Metalworking 20 May 3rd 05 08:30 PM


All times are GMT +1. The time now is 02:03 PM.

Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 DIYbanter.
The comments are property of their posters.
 

About Us

"It's about DIY & home improvement"