Why always me, and this is at the other place ! I mean the new old shop rather than the old new shop. There I usually didn't have as many problems like this, but today it happened.
This set was blown out in a storm, and it shows. A rebuilt LSB in now in the works unless I can figure it out. The set has been there a long time, we have the print, and today I thought it would be easy. It's having no problems holding memory like the other one, but it exhibits the same symptom as if the option code wasn't set right. When you swich to video, it loses sync but still feeds off the tuner.
At first I said "Piece of cake, the option code is off", I had that before. Well we got it hooked up and had a video source ready, and as I was just getting into the service menu, the thing quit.
Shorted HOT, and it blew one right away. I mean immediately, it's either the damper cap or the transformer. The damper cap checked good so I set out to find the transformer. The transformer was indeed the culprit, which was coinfirmed afer I changed it, but I couldn't find one.
This transformer is NLA, so if there isn't one in the boneyard, we are screwed, almost. This shop has parints for both the PTV 700 and 500 serues. It was on fiche so it wasn't all that easy, but I got it done.
Through careful examination I found that the two transformers are actually the same, just with different pinouts. I used a PTV500 series transformer in a PTV745. This require a bit of rework on the PC board. You have to cut foils and install jumpers, but it can be done. The set works.
We had to do this because we had a working set in our care and it fried out. Although it is not our fault, we really had no choice. If it hadn't have worked we would be in hot water, but it did work.
If someone needs, I can outline the procedure, but you have to very careful, when dealing with a reactive scanning transformer, the polarity matters. I mean a 9.5 V source becomes about 80 volts if the polarity is wrong, that is if it is trace rectified instead of retrace rectified. But it works and that ordeal is over.
So now, it has the problem of the video not switching, and not only did I set everything to what the print says I tried all the option values. They changed the selections in the menu, but nothing else.
Fianlly we dig up a board in the boneyard and it not only has a video problem, but the same problem as well. And again I've been through all the option codes. They both do the same thing. And neither has any sound.
I was thinking of looking at the video switching chip, but then why no sound ? I can hear a slight thump as the set powers up, so there is B+ to the output, and the speakers are good. I mean it sounds like the normal turnon transient, not a pop or anythinhg like that, and that is with either board.
Can it be the EPROM ? IIRC these are NLA but then one might be able to be programmed to it, but it seems to be holding the values, so what now, the micro ? Or should I think maybe these are lightning jobs and the I/O got FUBARED ?
This would have to be audio switching as well as video. If the data are sent to tell these chips what to do, it is stored in the EPROM, so is the micro screwing it up ?
And if so, both boards doing the same thing ? This almost sounds like a model specific thing, like there is an error in the print for the values or something like that. We looked, both boards are a GR6D, and designated an ASG026. They have exactly the same jacks and stuff on the back and are equipped identically. I looked. When I am about to put a boneyard board in a set I inspect it scrupulously.
Any opinions welcome. You never know, the customer might go for a new board if we can get it. But these other ones work except for a few flaws.
Any and all opinions from seasoned techs are appreciated. I'll be back on regular email soon, but I'd prefer the responses here, to help the industry.
Thanks in advance for anything you got. This is a bit too much coincidence.
JURB