screech in speaker when turning off set
 

So the Avante is acting up a little upon power off. Sometimes it makes a very short screech sound from the speaker when turned off and sometimes it's a bit longer. I'm not sure where to look on this one. It definitely is coming from the speaker.

Any thoughts?

Thanks

Check inside for owls... :D

Beats me.
See if it still does it with the volume down all the way. Also see if
you hear anything amiss between words in a show. . That may
narrow it down. If its a remote it could be coming from there
also.

BTW is this the set that had afterglow ?? If it is the two things
may be related. That concerns me ( HV)........

73 Zeno:smoke:
LFOD !

This is the set with jailbars and an intermittent jitter in image. I'm working on the jitter as it has to be vertical board and I've all but given up on the jailbars.

As luck would have it, it's not screeching anymore, or at least for the moment. The set is cold now, so it might need warming up. I'll run it for a bit and check it again.

A weak/bad filter cap can cause this. It was pretty common on early RCA XL100's but can happen on others. Could be the source of your jail bars as well.

Replaced all electrolytic caps on the chassis, but probably not on the sound board. I'll have to pull it and check.

My folks' second TV, a Crosley "Super V" 21" set from 1955, used to do that as well. I watched this set a lot as a kid, and remember it would make a screeching sound (not from the speaker, IIRC) when turned off. We never did figure out why. The TV worked very well otherwise, so we just left it alone until we got our next set some years later.

The Crosley was still making that sound, IIRC, when we relegated it to the basement (where it stayed from the '60s until the early '70s). It never occurred to me that filter caps could have been causing the noise, although I was just starting out in electronics at the time and knew very little about underchassis repairs (most if not alll of my "repairs" in those days on the old TVs I would rescue from the trash were done by replacing tubes).

Well I found the cause of the screech. It's the darn volume pot. I have cleaned it so many times, but it never helped. There seem to be dead spots and other issues internally. I have to go back and forth several times to get the sound just right. So scratchy and dropouts as I turn it. I found the perfect position and all has been well, but I guess that spot wasn't meant to last for ever. It started getting muffled, so I tweaked it again and now it is clear and the screech is gone.

I've searched for over 5 years for a replacement pot (63-10263), but can't find one. Some day I will find one.

Thanks for all the input, and if anyone knows where a volume pot can be found, let me know.

You'll probably have better luck searching for a replacement based on resistance (include taps if present), shaft length/type and mount style....the Zenith part may be long past unobtainium status, but there were probably several other makes that used a compatible part... even if there was not a similar part in other makes many pot kits gave one the ability to build up the correct pot from parts like Legos.... some antique radio pot dealers have the kits to build up a custom part.

The SM says it is 40K. Looks like it has three taps (two are tied together) and two wires connected. The shaft is just in the 1" range. I haven't found one that comes close enough to the resistance with that short of a shaft.

If you find one with the right resistance and taps, I think it would be possible to swap out the shaft.

I think I might just disassemble the current one and look for anything that might be fixable. I'm just afraid I'll mess it up more and be stuck with no volume. LOL

Like Jeff said about his parent's Crosley, I have a '65 Sylvania BW set that does this too, as the raster shrinks to a small square and disappears. It always did and still does last time I checked.

Show a pic of that pot, I may have one. I scrapped a few similar chassis.

Shafts can be swapped on the same brand of pots, its easy.
Mounting style does matter. Twist tab, nut, plastic etc.
Almost any VC from a flat chassis or hybrid should be the same
ohms. The uprights may be also. Remotes may use a different value.
Finding an NOS OEM pot is probably impossible. They were almost
never changed, cleaning worked for years. Only exception is if
it has an on/off switch. They were usually changed with OEM part
due to switch failure.
Last thing is be sure all the ground straps are well tightened.
They should run from main chassis to CRT, convergence, tuners,
secondary & primary controls etc. They are the heavy flat straps
covered in yellow plastic.

73 Zeno:smoke:
LFOD !