1960 Zenith SC 300 - ongoing repairs - Page 2 - Videokarma.org TV - Video

roundscreen · #16 03-25-2007, 06:38 PM

Adam.
Just a guess here, Take a good look at the ground pins. Have seen many zenith sets Where they crack and will cause weird problems. My 68 zenith had a problem with the video going out and it was a ground.
BTW- I like the roundie in your avatar, Really cool looking set.
Ed

Tubejunke · #17 03-25-2007, 09:22 PM

To elaborate on Jordan's comment you probably have a cold solder joint on one of your recent connections made while replacing components. Easy enough mistake to have happen...

Adam · #18 03-26-2007, 10:41 PM

You guys called it, I resoldered anything to do with horiz sync and now it seems good, it won't go out of sync all the way from one end to the other of the hold control, and syncs right when it starts up. I'll have to run it a while to be sure, but I think that was it.

""BTW- I like the roundie in your avatar, Really cool looking set.""
Thanks, I just picked it up a few weeks ago, I haven't started working on it yet except to check that the crt was good, it's the first roundie I've had with a remote.

Adam · #19 05-14-2007, 05:42 AM

I was watching this set, and the horiz went out again. It's strange how some sets just work, and others like this one frequently have components going bad. Compare this to the other 2 early 60s b/w Zeniths I have, the other two (that 23" console, and the 19" metal tabletop) had a much harder life, were stored outside for some time, the 19" was used so much the crt is a bit on the weak side. This set spent most of it's life sitting in it's original box, I can tell it was hardly ever used because the crt is so strong (I set the brightness nearly in the middle) , but I keep having to change resistors out of it. Changed nearly every resistor and capacitor (even some ceramics) in the horiz circuit. Whereas that 19" table top worked when I got it, and I just did a recap because I planned on using it alot. Never had a single component go bad on that set. The 23" had the usual leaky paper caps, and a few bad resistors, but worked good ever since I fixed it initially. But this one frequently needs repairs, I would just stop using it so much, but with space command and all it really is one of the sets I like best out of my collection, and it makes an excellent picture when it does work...

The problem turned out to be the 1meg resistor I circled in red in the schematic down below. It didn't actually test bad, but I found by shaking it around and heating it up while the set was on, that it was the source of my problems.

roundscreen · #20 05-14-2007, 07:11 PM

Glad you found the problem. That resistor may have been bad right out of the factory and that is why your zenith has low hours on it. It may have crapped out and the owner never paid to have it repaired.
In the old days we would call them dogs. Tube type sets are a pita to repair but still it is worth it.
Ed

Adam · #21 05-14-2007, 11:57 PM

When I first got this set, the major problem it had was it would produce no picture, just a blank raster, the problem turned out to be caused by this burned out little choke coil in the IF sections somewhere, probably did go bad early on, and just sat ever since.
The set worked fine for a while last night after I changed that resistor, but I turned it on today and got a similar intermittent horiz sync problem. I took it apart and ran it again poking around inside the chassis, this time that horiz AFC diode seemed to be causing the trouble, I swaped it with 2 1N4007 diodes I had (bought a pack of them several years ago and been using them to replace those selenium rectifiers in power supplies - those were my last 2), I wasn't sure if it was going to work at all or not, but it did and is still going, I'm hoping this is the last of the horiz problems with this set...

Adam · #22 05-15-2007, 01:21 AM

I just noticed I never posted any good pics of this set...here's one with and without the flash

roundscreen · #23 05-15-2007, 08:57 AM

Your set is cool and has a clear picture. If your set acts up again. check c51a and b, Have you replace that? I have seen them go bad before. Re check the ground that is connected to c51 too. Wrap a thin wire around the ground pin and resolder it again. The ground can break from the heat of the tubes and resistors. The osc tube is a 6gh8 so I take it you replaced it, If not, Try that. I am sure at some point you will find the problem.
Ed

Adam · #24 05-20-2007, 11:37 AM

I changed C51 last time it was having horiz sync problems. It's also got a new 6GH8. Changing that diode seems to have fixed the horiz for good, it's worked with no horiz problems for a while now.

Now currently the brightness control has become completely ineffective, the brightness is fine, the control just does nothing. Probably another bad resistor, this set seems to have more bad ones than good. It still baffles me how so many problems can arise with a totally re-capped low hour set. But I'm not going to pull the chassis right away to look at this one, as like I said before, it works like it is.

Adam · #25 06-02-2007, 07:41 PM

The brightness control problem turned out to be another loose solder connection.

Tubejunke · #26 06-02-2007, 10:07 PM

[QUOTE=Adam]This set was really the exception to the rule of these 60s Zeniths being nearly problem free, that one I just worked on with the broken crt mask had been sitting out in a barn for decades and used so much prior to that that the crt is a bit weak worked as is, this one that was packed in it's original box and hardly saw any use during its life, has had loads of problems. QUOTE]

This has been aninteresting read for me since I have a similar set, a 1959 Zenith Space Command that left me frustrated a couple of years ago and I have shoved it to the side. I posted at least on thread on the set but came up with nothing. Like your set my set looked as if it had VERY little use. I thought it would be no trouble at all to bring back to life. The set had a hum for sound with no evidence of picking up a signal. It also had no vertical sweep. I recapped the set and replaced a bunch of resistors and ended up with the same exact performance. I was disapointed to say the least.

I guess some time I will have to investigate further by checking every connection against a schematic as I did see evidence of at least one older repair. Yes! In the vertical section. Perhaps that is where everything went wrong with this set, a botched repair and the set was put to storage. Like me the old owner may have thought it was too beautiful to trash. Also the added attraction of being a 24" remote set makes it hard to trash.

I feel like ONE crazy thing will bring my set to like new condition. I hope I can find what that ONE thing is.

Anyone know whare to find a remote??

Adam · #27 06-03-2007, 03:02 PM

""The set had a hum for sound with no evidence of picking up a signal.""

A 23" 1961 Zenith b/w console I have had that problem, turned out to have a few bad resistors in between the power supply and the IF sections. A 1971 19" b/w Zenith I don't have anymore also had that problem, it was just caused by a loose wire going to the filament on one of the IF tubes, causing it to not light up.

Those remotes show up on ebay alot, also they seem to be interchangeable, I use my SC600 remote on this set all the time. The buttons don't exactly correspond though, channel lower button changes the channel, and the channel higher is on/off-vol.

Adam · #28 09-09-2009, 11:50 PM

restoring another lost post ...

I had put a lot of hours on this set lately. Usually watching it at night and then falling asleep with it on. It developed intermittent sound, and the remote quit working. The sound troubles were caused by a weak sound detector tube, 6BN6. The remote problems were caused by a resistor that failed open connecting the grid at pin 6 to the 285v B+ at the 2nd amp (6AU6). Here's a picture of the back of the set with the chassis installed: http://www.audiokarma.org/gallery/sh...ze=big&cat=503