I Have posted before about this set stumping me. I brought it home a few years ago with little or no vertical sweep and only a hum for sound that is adjustable with the volume control. I thought it would be the typical capacitor problems that most old sets have, especially with the hum.

Well I replaced nearly every capacitor in this set with the exception of the ceramic disc type and one paper cap in the horiz. section. I checked and changed a few resistors too. I still have the EXACT same performance from this stubborn set.:scratch2: Not one bit of improvement. I couldnt believe it. One of the thrills of replacing caps and resistors is watching the lifeless slowly come back to life.:no:

I'm hoping there is someone who is really familiar with this type chassis and its typical problems. The set is a Space Command and I have wondered if a short in the remote chassis could somehow cause the main chassis to go whacky. I cant see it effecting the vertical sweep. If memory serves me right I tried unplugging the power connector to the remote chassis and the set does not power up like that. I may be wrong.

All the tubes check out. The power supply, horiz, and HV work fine but thats it. Just hoping for some clues on where to go with this. I have heard that the Zeniths of this type and time frame were very good performers producing a superb picture. This chassis design was used for several years so I hope for some good results as far as our great knowledge base.:thmbsp:

C'mon, somebody's got to have something to say about the old Zeniths.

I know its hard to troubleshoot someones set based on descriptions of problems. I just hoped maybe there was some common problem with these common chassis. The only thing I havent looked into is the ceramic disc capacitors. I noticed some of them are multi sectional. That was a new one on me. Perhaps I will find the troubles there. Not much left.....

Tube,
Those are called networks. Its the same type or similar of networks that were used in the Predicta's that gave alot of problems. Some of those networks have resistors built into them also along with the caps. I would definately check those because any one of them could kill your vertical sweep. Have you checked your vertical output transformer and the yoke? If you have a schematic i would start with checking the voltage readings and go thru the process of elimination. Sounds like you might have a video output problem too since you get weak audio but no apparent signs of recieving a channel. Sounds like your not getting proper voltage somewhere. Does that set use selinium's? Check those also and if in doubt replace. Dont know what else to tell ya. Hopefully someone with more troubleshooting skills will pop in soon. Good luck!
-Tony

Sounds like good tips to me, Hmmm? ..... Those old sets, Yep, it's a vertical problem....... :)

Its the same type or similar of networks that were used in the Predicta's that gave alot of problems.
This article shows how I replaced one of the networks ("couplates") in my Predicta:

http://www.antiqueradio.org/philc12.htm

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

SAMS usually gives the equililent circuits to the networks. The ones that look like 3 legged ceramic caps are your culprits. When you rebuild them, the cap values are critical. There is no leeway. If you have seleniums, the only way to test them is to evaluate the sound as they hit the bottom of the garbage can.

Well I replaced nearly every capacitor in this set with the exception of the ceramic disc type and one paper cap in the horiz. section. I checked and changed a few resistors too. I still have the EXACT same performance from this stubborn set.:scratch2: Not one bit of improvement. I couldnt believe it. One of the thrills of replacing caps and resistors is watching the lifeless slowly come back to life.:no:

All the tubes check out. The power supply, horiz, and HV work fine but thats it. Just hoping for some clues on where to go with this. I have heard that the Zeniths of this type and time frame were very good performers producing a superb picture. This chassis design was used for several years so I hope for some good results as far as our great knowledge base.:thmbsp:

You may want to double check some of the tubes, perhaps they tested OK but are unable to function in-circuit. Maybe the video and IF tubes for starters. Just a thought, as sometimes the tubes can be deceiving.

Gilbert

Thanks for all the thoughts and tips fellows!! To clarify a couple of things, first and luckily the set uses a power transformer instead of selenium rectifiers. I feel pretty good about the power supply being strong as the set is producing DC just fine.

NOW, about these "networks" we have had mentioned. I need to look into this, and real good. There just happens to be one of them in BOTH the vertical AND the sound sections. I have never run into these before, but I am glad at least one person says that they are troublesome. I left them alone in my recap because it seems to be a rule of thumb in our hobby that the ceramic discs can be overlooked to a large degree. Most seem to be single section, not multi..

Someone asked if I had checked my yoke and output transformer. Well yes and no. As far as the transformer I only have put an ohm meter across the windings for a continuity check. I dont know what lind of resistance readings to look for in a good/bad trans.

Concerning the yoke, I have an old Eico Model 944 flyback and yoke tester that likely needs more restoration than the set I am working on. Maybe a good time to see what the old Eico can do. However I would think that a bad yoke would more often cause a distorted sweep or "keystone effect" as opposed to a nearly (1/2") complete loss of sweep.

Right now I'm hoping these crazy "network" capacitors are the trouble. This set should do well for many years as it seems to have very low time in use. Mostly all original tubes were in place when I got it and very little black inside the HV cage. Perhaps this trouble caused the set to be put aside in its early years.