Zenith 10S690 Volume Control Issues

[vortalexfan]

OK. so question, what is this coil for?
See picture attached below.

I'm asking because when I was cleaning out my volume control pot earlier with the contact cleaner I accidentally got a bunch of contact cleaner on this coil assembly and I'm wondering if me getting contact cleaner on this coil assembly might of messed something up with the radio's reception.

This is the only other thing I could think of that might of been messing things up.

Thoughts?

[vortalexfan]

OK, so I don't know what I did to it, but now the tuner is working again.

[vortalexfan]

OK well, I tried it out again now that I got the tuner working again, and the volume control quit working again and it started working like a tone control knob again.

I double checked EVERYTHING and there isn't anything wired up wrong and the volume control pot isn't open, so it seems like I'm chasing down some sort of weird electrical phantom in this radio...

Any other ideas as to what could be causing my volume control issues?

[vortalexfan]

OK so the only thing I can think of is that one of the capacitors that is attached to the negative end of the volume control pot might of went bad or were faulty, in the physical radio itself there are 2 capacitors that are going off of the volume control pot negative leg, which is weird because looking at the schematic there's only one capacitor coming off the Negative leg, which is C14 unless I'm missing something...

In the actual radio chassis, there's a mica capacitor that's going between the negative leg of the volume control pot and one of the taps on the volume control pot, which that mica capacitor isn't marked on the schematic (at least not that I can see of anyways) there's 2 capacitors marked on the schematic in that area that seem like they might fit the description of a mica capacitor value wise but the way they are drawn on the schematic they don't seem to connect from the tap of the volume control to the negative leg of the volume control pot, C12, which is a 350 pF capacitor is one possibility, the other is C9 which is a 25 pF capacitor, but like I said none of those capacitors appear to have a physical connection with the volume control pot negative lead and the tap on the schematic.

[old_coot88]

When you had the bottom lug of the control disconnected, did you actually verify with an ohmmeter that the element isn't open?

[vortalexfan]

Originally Posted by old_coot88

When you had the bottom lug of the control disconnected, did you actually verify with an ohmmeter that the element isn't open?

yes I did, it didn't measure O. L. which usually means its open, it actually gave a value of 2.5 Meg like the schematic said it should of, as for whether or not I could get a smooth up or down movement of the numbers when rotating the knob, I couldn't get it to do that because I couldn't hold the meter probes onto the terminals and turn the knob at the same time, I tried to use an alligator clip to hold one of the meter probes onto one of the terminals while I held the other one in place with my left hand and turned the knob with my right hand but the alligator clip kept coming loose and the negative lead of the probe kept falling off the negative terminal of the volume control pot so then I couldn't get any sort of readings, one way or the other.

[old_coot88]

Well, since it showed the called-for 2.5 meg, it ain't open. Since turning the control affects the tone, does it change the volume at all? And what is the actual volume level? Is it full volume, or partial, or... ? For the heck of it, try disconnecting those two tone taps. That way, the control becomes just a plain potentiometer with no junk hanging off it.

[vortalexfan]

Originally Posted by old_coot88

Well, since it showed the called-for 2.5 meg, it ain't open. Since turning the control affects the tone, does it change the volume at all? And what is the actual volume level? Is it full volume, or partial, or... ? For the heck of it, try disconnecting those two tone taps. That way, the control becomes just a plain potentiometer with no junk hanging off it.

The volume level is between 1/8 and 1/4 volume level, and the volume control knob doesn't affect the volume at all, all it does is affect the tone and that's it, and the weird thing is that the tone control push buttons don't do anything to the radio except for the one marked "Normal" the rest of the tone control push-buttons don't do anything to the audio on the radio.

I'm wondering if one of my capacitors that I installed in the tone control/volume control circuit wasn't faulty or defective from the factory.

[Electronic M]

Have you done any signal injection testing to isolate the problem to a single stage yet? ISTR you recently bought RF generators (and they presumably have audio generator functionality too).

Inject audio (put a .1uF in series with your generator to protect it from DC) on the audio side of the detector if the set passes audio test the IF/RF system ( injecting IF frequency from the detector to every grid and plate back to the antenna) if it doesn't pass audio then trouble shoot the audio system by moving audio injection point to every grid and plate between the detector and speaker. If you know where the buck stops in the signal chain then you have isolated the problem to the components associated with 1-2 tubes....that is a heck of a lot easier than guessing where it is out of the entire radio.

[vortalexfan]

Originally Posted by Electronic M

Have you done any signal injection testing to isolate the problem to a single stage yet? ISTR you recently bought RF generators (and they presumably have audio generator functionality too).

Inject audio (put a .1uF in series with your generator to protect it from DC) on the audio side of the detector if the set passes audio test the IF/RF system ( injecting IF frequency from the detector to every grid and plate back to the antenna) if it doesn't pass audio then trouble shoot the audio system by moving audio injection point to every grid and plate between the detector and speaker. If you know where the buck stops in the signal chain then you have isolated the problem to the components associated with 1-2 tubes....that is a heck of a lot easier than guessing where it is out of the entire radio.

I got it to receive radio signals again, it was the Phono/Radio Switch that was causing the problems, I got switched to phono mode rather than radio mode.

The main thing causing problems right now is the volume control still giving me troubles, and signal injection isn't going to help me troubleshoot a malfunctioning volume control pot.

I'm still wondering if it isn't something with the capacitors I installed in the volume/tone control circuit.

I really wish I would of taken a picture of the underside of this radio before I worked on it so I could of seen how things were wired up originally so I could make sure I didn't accidentally install a capacitor in the wrong spot.

does anyone have a picture of the underside of this radio that they could post so I can make sure I didn't accidentally install a capacitor in the wrong spot?

[dieseljeep]

Originally Posted by vortalexfan

OK I got the volume control issue fixed but now I've got a new problem, I'm not getting any stations in on any of the bands on this radio, and it was working just fine before I worked on the volume control issue.

It seems like this radio is developing one problem after another...

I guess I should of just left it alone seeing as it was working fine before I replaced the capacitors in it.

I don't think I've ever repaired a radio that was this touchy before.

After working on these old relics for well over 60 years, I learned from my mistakes. For one thing, I never "shotgun" the project. I replace components in stages. Taking out the chassis and speaker and putting it on the bench to check or find out what the real cause is. If the set works, so much the better!
Then do the electrolytics and audio coupling caps.

[vortalexfan]

Originally Posted by dieseljeep

After working on these old relics for well over 60 years, I learned from my mistakes. For one thing, I never "shotgun" the project. I replace components in stages. Taking out the chassis and speaker and putting it on the bench to check or find out what the real cause is. If the set works, so much the better!
Then do the electrolytics and audio coupling caps.

That's probably what I should of done with this set, because it was working for the most part, except for the AVC circuit which was acting wonky, it would make distant stations that would come it pretty clear at night fade in and out audio wise which were otherwise coming in really well, and the schematic for this radio didn't have the AVC circuit marked very well.

So that's why I just decided to replace all of the paper caps in this radio because I wasn't sure which caps were part of the AVC circuit in this radio (the AVC Bypass Cap).

Also I know for a fact that this radio's orginal Filter caps are still good in this radio because a.) the radio has no 60 Hz Hum whatsoever, and b.) I just got a nasty jolt from it when I was trying to take the chassis out of the cabinet even after the radio had been unplugged for more than a half hour.

Also the interesting thing is that this radio was bone stock original, there were no capacitors replaced underneath the chassis, it still had all of the original Zenith Capacitors underneath the chassis when I got this thing and it was working like new with the original caps still in place and the capacitors didn't show any signs of having any wax dripping from them in fact about 99% of the original capacitors underneath still had their factory molding marks in the wax on the sides of the capacitors yet.

This radio has all of its original Zenith tubes in it yet except for the 6A8 and the 5Y4 rectifier tube which are the only non-Zenith re-placements in the radio.

Besides the water marks on the top of the cabinet that is presumably from a plant being set on top for years, this Radio was like brand new, almost like it was mostly a display unit for most of its life.
I'm thinking maybe once the family got a TV in the 1950s the Radio just became a display piece, which might explain why it was such a low hours set.

[vortalexfan]

OK so looking at the picture posted below, was there something attached at the point circled in the picture, something like a capacitor perhaps?




I'm wondering because maybe I had accidentally wired a capacitor in the wrong spot and that's what's causing my volume and tone control problems.

[vortalexfan]

OK so I figured out why my volume control isn't working, I forgot to install C11, the only problem is that I don't have that part, because I forgot to order it, because I accidentally ordered two .0022 MFD capacitors rather than a .0022 MFD and a .022MFD capacitor. weird thing is that I didn't even get that second .0022 MFD capacitor in my order, so I didn't even have that capacitor to begin with.
I have lots of .2 MFD Capacitors but I don't think that would work in that spot when it calls for a .02 MFD.

I do have a .01 MFD Capacitor I wonder if that might work in the place of C11?

To borrow the words of Homor Simpson: Doh!

[old_coot88]

'Oly 'ell old chap!! That's the main coupling cap from the detector TO the volume control. The audio that's getting through is residual bleed past the volume control. Value's not critical. A .01 will work fine with possibly a slight reduction of the bass.