1982 Zenith System 3 Problems

[NowhereMan 1966]

Originally Posted by JohnCT

Okay, here's the thing: Zenith servicers hated that toilet. There, I said it... I remember getting two bad 186 modules in a row from Zenith. If you can find a new (yellow label), grab it. Any red label version was "rebuilt" using questionable techniques.

Take a look a the board/metal plate assy the 186 sweep board is mounted to. There are three TO-92 start-up transistors on the small board near the top edge. See if they are blown. If they are, replace all the electros on the 186 board as well as the transistors (and IIRC, a resistor or two will be scorched). There is a lot of voltage on those transistors so choose your subs wisely.

On the main 181 board there is a dual section PC mount electro. Good probability one side is bad if it's never been changed. If one side is bad, it causes all sorts of collateral damage when it opens including tormenting that start circuit and blowing those transistors.

If all those are good, turn the main board over and resolder every heavy resistor on the board. They usually are mounted in small metal grommets before soldered. What causes many guys to miss this is that the connections look fine, even under a loop, but they go bad. Put some liquid flux on them and reflow them with a decent wattage iron.

If you had the boards out, don't overlook the possibility of getting a connector crossed. The boards are printed so carefully check the legend on the board to the connector number. Fortunately, Zenith was good about clearly labeling those connectors.

John

It did have a yellow label on it. I know with the old board, the TV might come on for a few minutes and shut off and if you try to turn in on, it would "motorboat" indicating a bad capacitor from my discussion here. It just seems perplexed that nothing happens, I guess I'll have to go over it again. I'll have to check around with my VOM with my SAMs folder in hand and see what's up.

[zeno]

You need to find if this is a start problem or something else.
If the set does not start properly there is a resistor on the
small PCB (2 K IIRC) that will burn. Start process is....

The little board turns on & supplies a pulse to the hoz drive
This is the separate wire with plug.

The HV comes up.

A secondary B+ voltage is developed off the FBT & runs the horz osc IC.

The little board gets turned off & set runs.

If it does not start the set tries to run off the little board. It then burns
the resistor & sometimes transistors.

73 Zeno

[JohnCT]

Originally Posted by NowhereMan 1966

It did have a yellow label on it. I know with the old board, the TV might come on for a few minutes and shut off and if you try to turn in on, it would "motorboat" indicating a bad capacitor from my discussion here. It just seems perplexed that nothing happens, I guess I'll have to go over it again. I'll have to check around with my VOM with my SAMs folder in hand and see what's up.

If it's a yellow label and was sealed, it's likely good, even sitting in the box all these years.

First thing I would do is reinstall the original module and see if you can get back to where it was. If it acts dead like the new board, then something else happened coincidentally. If the original board runs with the shutdown and motorboating, pull that dual section PC mount electro and check it, or better yet just replace it. That cap causes all sorts of mischief including damaging the start transistors on that sub board I mentioned earlier.

On Zenith modules, the suffix is critical. I used to have all those boards memorized, but whereas a 9-181-01 might sub the 9-181, the 9-181-02 might not, but the -03 might!

Our local Zenith distributor (Plymouth Electric NH CT) used to mail us cheat sheets that had all the modules listed with the suffixes that would interchange. Saved a lot of time and trouble. All that stuff I tossed out twenty or more years ago.

John

[NowhereMan 1966]

Originally Posted by JohnCT

If it's a yellow label and was sealed, it's likely good, even sitting in the box all these years.

First thing I would do is reinstall the original module and see if you can get back to where it was. If it acts dead like the new board, then something else happened coincidentally. If the original board runs with the shutdown and motorboating, pull that dual section PC mount electro and check it, or better yet just replace it. That cap causes all sorts of mischief including damaging the start transistors on that sub board I mentioned earlier.

On Zenith modules, the suffix is critical. I used to have all those boards memorized, but whereas a 9-181-01 might sub the 9-181, the 9-181-02 might not, but the -03 might!

Our local Zenith distributor (Plymouth Electric NH CT) used to mail us cheat sheets that had all the modules listed with the suffixes that would interchange. Saved a lot of time and trouble. All that stuff I tossed out twenty or more years ago.

John

Well, good news, sort of..... I had the same idea myself, put the old board in to see if she will motorboat. Well, she did a ittle but I got her up and running, right now the old girl is playing Bonanza. I still have the same old issues with the picture with a red tint and raster lines on the right side of the pic from time to time, sometimes it clear, sometimes not, it does look a little washed out on the right. The new board I have is a 9-181 main board, I put the chips and MOSFETS in but nothing there but the old board still works with these issues. There was time she would run for 5 minutes or less and cut off, but she's been going for over 30 minutes now. Still I'll power her down soon until I can fix her properly or find someone to help me. BTW, the old board is a 9-181-02. Seeing that I was able to get her going, sort of, I feel proud of myself. at least I got it back to where it was.

[zeno]

The shading is the classic symptom of the cap I told you about. ( C3496)
Find it & change it. The cap JohnCT mentioned was common & usually
has all kinds of mung leaking out under it before it opens. Rob that
off the other 9-181 for now.