Are These Circuit Traces Bad - Videokarma.org TV - Video

TinCanAlley · #1 08-07-2013, 02:24 PM

I purchased an NOS horizontal output board for my Avanti and upon installing it, nothing. There's sound, but no image. Not even the sound of the degauss. So I swapped back the old module and it worked again. I check everything on the top side of the module to make sure they were in their sockets, etc. Everything looked fine. It's when I turned the board over. I noticed that a few of the silver traces had black sections that look like the old laserdiscs had when they got laser rot.

Anyway, I'm attaching a pic and would appreciate any input. I bypassed the main canister today and it didn't help with the jail bars. I don't feel I wasted my time as I had already replaced all electrolytic caps earlier. Besides, the 500uf sections were 35% and 40% on the plus side and the 400uf sections were about 25% and 30% on the plus side. Not sure this makes too much of a difference, but the ones I put in are only 10% when tested.

Thanks

TinCanAlley · #2 08-07-2013, 02:59 PM

Never mind. I decided to test the transistors on the board (figured one could be bad). I'm not an expert at testing, but found one that seemed odd, so I decided to take the one from the working module and swap it. When did that and installed the board, the set fired right up.

Now I need to get new transistor.

Thanks

zeno · #3 08-07-2013, 05:05 PM

The etch is fine. I have seen it before , I think its magic
marker.
On Zenith modules its common to have bad plug in IC &
transistor sockets. Especially on the upright ( 25EC45 etal )
chassis. They eliminated them I think on all rebuilt boards.
The sockets are less reliable than the parts !

73 Zeno

TinCanAlley · #4 08-07-2013, 05:52 PM

Quote:

Originally Posted by zeno

The etch is fine. I have seen it before , I think its magic
marker.
On Zenith modules its common to have bad plug in IC &
transistor sockets. Especially on the upright ( 25EC45 etal )
chassis. They eliminated them I think on all rebuilt boards.
The sockets are less reliable than the parts !

73 Zeno

I tried the original transistor again and the set wouldn't fire up. Putting in the one from the old board in again worked. So now I need to find me an NTE171 locally. Not gonna spend a couple of bucks for one and then $7 for shipping.

Interesting, though...The jail bars are still there after all this work. The image is better, though. I tried the video processing board I got and it was a disaster. It's an update board and NOS, but when I fired up the set, the horizontal was screwed and the control on the back of the set couldn't fully correct it. The color was also messed up. Some areas were black and white with flashing colors now and then and the brightness and contrast were messed up as well. I figured it was safer to put back the original board than try to adjust setting to see if the new board was working properly

zeno · #5 08-07-2013, 06:47 PM

You need to be careful with any brand boards in the box.
They are quite often the bad boards. Someone changes it &
never marks it as bad. Many shops were careless about
returning duds for core credit, often loosing track of where they
came from etc. No invoice -no credit.......
Also many put them aside to rebuild themself "when a chassis
comes in & I got time" Needless to say that usually was never &
bad boards piled up. Then someone comes along 30 years
later & liquidates them on E-Bay. No way in hell he knows.

CAVIAT EMPTOR

73 Zeno

Findm-Keepm · #6 08-07-2013, 07:19 PM

Quote:

Originally Posted by zeno

You need to be careful with any brand boards in the box.
They are quite often the bad boards. Someone changes it &
never marks it as bad. Many shops were careless about
returning duds for core credit, often loosing track of where they
came from etc. No invoice -no credit.......
Also many put them aside to rebuild themself "when a chassis
comes in & I got time" Needless to say that usually was never &
bad boards piled up. Then someone comes along 30 years
later & liquidates them on E-Bay. No way in hell he knows.

CAVIAT EMPTOR

73 Zeno

I quite agree - when my dad retired back in 2008, he had exactly 7 good Zenith Duramodules and about 30 boxes marked with the symptoms the module had. After the heyday, and after junking a few sets, shops ended up with lots of questionable stuff.

Quote:

Originally Posted by TinCanAlley

I tried the original transistor again and the set wouldn't fire up. Putting in the one from the old board in again worked. So now I need to find me an NTE171 locally. Not gonna spend a couple of bucks for one and then $7 for shipping.

As far as needing a transistor, post the 121- number, as many of us have stashes of original parts - yours for postage, in my case. Don't default to buying new stuff when we might have what you need, and are willing to give it away!

Cheers,

old_tv_nut · #7 08-08-2013, 01:30 PM

What do you mean by "invisible" waves?

TinCanAlley · #8 08-08-2013, 02:02 PM

Quote:

Originally Posted by old_tv_nut

What do you mean by "invisible" waves?

Okay, how about transparent waves. You can see the waves as they run upwards and then downwards, but they are clear. It's just the slight distortion they case to the image that lets you know they're there.

I tried to capture them via video, but it's harder than it would seem. I'm still trying, though.