Hitachi part-HC-3041 AP43 chassis

What caps did you change? All the ones inside the comb filter and the pip module?

I didn't do the PIP module because in an AP43 main video doesn't go through it. I've unplugged them with no ill effects, even the PIP window comes up, without child video of course. (actually IIRC the PIP worked fine on this set)

Anyway I did change ALL the lytics in the comb filter, first the ones that checked bad and all of the same value. When the problem persisted I thought maybe one was leaky (brightness too high seemed to be in line with that reasoning, maybe), still no good.

I finally got a 2 line comb filter to work. You have to couple the video from the input to the "YSY" terminal. I used a 10uF cap. Not a perfect solution, but it was a solution.

Another very interesting thing about this job is that at turn on, the set has a small white dot slightly below and to the right of the center of the screen. It goes away as soon as you use any function that invokes an OSD. It has to be the micro, but I can't hold up the job.

I also had to fix the convergence board, had a crack in it, I replaced it with one from the boneyard because,,,,, I could. The AP 43 has a pretty good control set and even full blown convergence only takes me about 20 minutes, if that.

One thing almost tripped me up, but I was already hip to it, I slide the chassis in and reconnect the speakers etc., then turn it on. (I had checked the video input/switching board caps because of the symptom. I'm sure something on there could possibly cause my original symptom). I got it in an fired the set up and had interference lines in the video. Then I realized I hadn't yet strapped up the wires. This was a case where convergence was deflecting with noise from the SMPS. I initially thought it was in the video, but moving the convergence output lines away from the SMPS cured it.

Let that be a word to the wise, when you have a really elusive video interference problem on an RPTV, take a minute and disable the convergence. I've had this appear to be a video problem more the once, the first was an NAP PTV 5 or 600, the last one without digital comvergence. The PLL of the WF generator chip was not in sync. I've also seen it on a Zenith (9-1674 based chassis), but this Hitachi wasn't a hard failure, it was lead dress.

JURB

I am curious as it has been years since we had the last one of those in. Were the capacitors in the comb filter non-polarized ones? I seem to remember a similar problem when a tech put polarized capacitors in one where non-polar ones should have been used. But I cannot remember if it was the Hitachi RPTV set or not.

I believe there were three, all 10/16. I did replace them with regular lytics, but 50 volt units. I have done this before, as long as you use a high enough rated cap you can get away with it.

Let's face it, the whole thing runs on 9 volts, and if they're using an np cap there, that means they expect the polarity of the applied voltage to change. It's also a good bet that it's a signal coupling cap and not likely to see even the whole 9 volts.

A 10/50 can easily take 3 volts reverse. If some tech caused a problem it was probably a cap with a low voltage rating.

You didn't say that you do, but you, or your organisation should not summarily condemn RPTVs based only on age. There are some units that have held up quite well. More on this in another thread, I'll start it later.

JURB