1989 Jvc - Page 2 - Videokarma.org TV - Video

karmaman · #16 01-07-2008, 04:26 PM

It's actually a 4.7uF 350V cap, and it tested 10.1nF. I've never seen a cap test this bad before. Will be going to Fry's later today. Any other caps I should check?

MRX37 · #17 01-07-2008, 04:47 PM

Quote:

Originally Posted by karmaman

It's actually a 4.7uF 350V cap, and it tested 10.1nF.

There's your problem.

I got that samsung that needs C950 replaced, but I can't find it. I suppose i should take it out and go through the larger caps again...

karmaman · #18 01-07-2008, 11:57 PM

That was most definitely it, thanks radiotvnut. The set has some slight pincushioning, any suggestions on what cap might be causing that?

radiotvnut · #19 01-08-2008, 12:30 AM

This set does not have any type of pincushion correction circuit or any adjustments. There are 3 caps in the horizontal output transistor collector circuit that could have drifted in value and be causing a width problem. These are high voltage capacitors and their values are critical. They should only be replaced with the same value and equal or higher working voltage. Failure to do so could result in HV running above normal. In the '70's, Zenith used a high voltage capacitor in this circuit that was prone to open. The result was the HV running so high that it would arc through the neck of the CRT and literally blow the neck off the tube! Anyway, here are the values.

C524 .0056 uF, 1.6 KV, 3%
C526 .27 uF, 200 V, 5%
C527 330 pF, 2KV, 10%

karmaman · #20 01-08-2008, 05:14 PM

Thanks, I'll check those. It's not really pincushioning, just bad regulation, sometimes if a bright object is in the middle of the screen it kinda bulges out, so I mistook it for a pincushion problem. Interesting about those 70's Zeniths. I guess that's why it's hard to design something, such a problem would only show up after a few years of use!

radiotvnut · #21 01-08-2008, 05:41 PM

Check the voltage at the + terminal of C908 (100uf, 160 V). It should read 130 VDC. The voltage should remain around 130 and should not flucuate with changes in brightness. If the voltage is off or fluctuates, there is a problem in the regulator circuit. C908 could be the cause. Use caution when checking voltages. Most TV's have a "hot" chassis and can deliver a possible lethal shock if you touch the chassis while another body part has a path to ground.

karmaman · #22 01-09-2008, 11:24 PM

C908 was at a healthy 110uF, so it's good. I didn't measure the voltage at it. I think I'll leave this TV as-is for now, the regulation problem is really non-noticeable as it only shows up every now and then depending on what's on the screen. One thing though, this set has a really noisy flyback. I can hear the whining a lot louder than on most sets. Even my friend who was over the other day noticed it. Is this how it's supposed to be, or is there anything I can do to quiet it down a little?