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-   -   1970 Zenith 21" color with the SC600 remote (http://www.videokarma.org/showthread.php?t=270199)

Adam 02-27-2018 08:09 PM

1970 Zenith 21" color with the SC600 remote
 
14A9C50 chassis (one of the early hybrids with no modules) in the metal cabinet…

When I got this set (at the fall etf) I was told it had no HV. But I plugged it in today, and the HV is fine. Although there are several problems with it, which are as follows:

1. color oscillator - It has those color bars rolling up and down the screen

2. no sound - and, yes, I already tried flipping the auto/manual switch to manual

3. power tuning doesn't work

4. none of the remote stuff works at all

5. cosmetic stuff: missing a few knobs (which I might have), The back and bottom of the cabinet is rusty, the inside of the cabinet is rusty, chassis is a little rusty. But nothing so bad that it actually has eaten away any metal, and the outside fake woodgrain part of the cabinet looks good, and strangely, the antenna is actually unbroken. If this wasn't a rare remote set I wouldn't bother, but I suspect I'll probably wind up repainting the back, bottom and inside of the cabinet.

I'll post some pics later...

Marco-nix 02-28-2018 08:36 AM

First of all, you need to de-rust all grounds and clean all around the chassis ..

Adam 06-19-2018 05:15 PM

So I've fixed the sound, the color (except for a broken blue convergence pot - I have a spare convergence board for this, but the same pot is bad on that one too!), and the remote issues that were electronic (not yet the ones that are mechanical, which are many).

But it's developed an HV regulation problem I have not been able to sort out. At first the picture was blooming out, then going black, when the brightness went up. After changing the HV rectifier, it stopped doing that, but the HV still drops as much as 5KV with variations in brightness and the picture pulls in on the left side. I've been working on this set on and off for months, yet have not been able to find a single defective component that could be causing this beyond that one tube.

zeno 06-20-2018 06:52 AM

For the HV 1st be sure the damper & reg tube match the
tube chart, do not sub. Sometimes they show 2 different
pairs you can use. But most likely its the VDR. Trouble is
even the NOS ones are going bad in the package. Doug,
DRH4683 did great work finding a modern sub. Find
that thread ! Also watch out for high ohm resistors in
the reg area.

IIRC it was the left blue horz control & went bad in all of them.
Came as a kit with a power resistor. I dont remember the
details but probably subbed from a 63- number to an 800- number.
There are a few lists out there of NOS parts FS out there & you
may find one.

For remote the only things I remember was the rocker SW on the
rear of the TNR.

73 Zeno:smoke:
LFOD !

Jon A. 06-20-2018 05:40 PM

I saved the VDR replacement info to a text file a while ago.

Quote:

The best performing modern MOV varistor was made by KOA Speer, type NVD14UCD430

Adam 05-15-2020 11:32 AM

I'm returning to this TV after not working on it for nearly two years.

Back in 2018, I eventually swapped these tubes with new ones: HV reg, damper, HO, HV rect. I also swapped the VDR, using the one specified in Doug's thread: http://www.videokarma.org/showthread.php?t=261780 And I changed one of those 22meg resistors which had drifted up to around 35M.

But none of that fixed it.

When I fired it back up a few days ago the HV was stuck down around 15KV. I also noticed there was no (or very little) focus voltage. I put in a new focus rectifier, and the HV went back up, but still no focus voltage. I tried a second replacement in case that one was bad, with the same result. Could I be looking at trouble in the flyback itself?

zeno 05-15-2020 03:50 PM

There are a few hi ohm 2W resistors in the focus on the fiber FBT board IIRC.
Check them 1st. Also the spark gaps in the CRT socket can short. Just
unhook the focus wire & see if the F at the chassis comes up to 5-7 KV.
If it goes beyond that I will pull the manual if I got it.

BTW FBT's on most tube color sets will kill the raster & give little or no
HV etc.

73 Zeno:smoke:
LFOD !

Adam 06-18-2020 02:18 PM

1 Attachment(s)
The only one of those resistors that was bad was a 22meg that had drifted up to around 35meg, (circled in the schematic) which I had already changed. Disconnecting the wire going to the CRT socket made no difference.

Electronic M 06-19-2020 09:26 AM

Are you sure the original VDR was the part Doug figured out that replacement for? I remember from Doug's thread that Zenith used 2 different HV VDRs in different chassis. Doug's replacement was for the more common one.


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