Zenith 10S690 Volume Control Issues

[vortalexfan]

Hello Everyone, last night and early this morning was spent recapping my Zenith 10S690 Radio and after I finished recapping it and struggling for about an hour trying to get the chassis back into the cabinet (I was having a hard time getting the chassis screw holes to line up with the cabinet holes for the screws to go into to secure the chassis to the cabinet).

I plugged in the radio and turned it on to test out my work and sure enough my volume control wasn't working right, instead of raising and lowering the volume like its supposed to it instead acts like a tone control, and my tone control switches don't work except for the one marked "Normal".

I was trying to be careful to observe where each capacitor went when I was removing the old ones and installing the new ones and only replacing one capacitor at a time.

I've looked over the schematic for this radio and I can't seem to figure out what could be causing this issue, the radio was working fine prior to the recap (just had an intermittent AVC circuit that was more than likely due to a leaky AVC Bypass Cap).

Any ideas as to what might be causing my problem?

The schematic for this radio is posted below.

Any help with this matter would be appreciated.

[old_coot88]

An open at the ground end of the volume control would cause the problem you describe. Either an open at the end of the resistive element, or at the external ground connection. Hopefully the latter.

[vortalexfan]

Originally Posted by old_coot88

An open at the ground end of the volume control would cause the problem you describe. Either an open at the end of the resistive element, or at the external ground connection. Hopefully the latter.

Ground end of the volume control? There's no ground connection indicated on the schematic for the volume control pot, and the volume control pot isn't connected to ground anywhere according to the schematic, there's a reference to ground on the tone control keyboard itself but not not on the volume control pot.

[init4fun]

Originally Posted by vortalexfan

Ground end of the volume control? There's no ground connection indicated on the schematic for the volume control pot, and the volume control pot isn't connected to ground anywhere according to the schematic, there's a reference to ground on the tone control keyboard itself but not not on the volume control pot.

I think ol Levi here could use some schematic reading lessons , the side of the volume control pot at resistor R12 is at B- potential , which is a HELL of a lot closer to "ground" than it is to B+ , that's for sure .

Old coot 88 knows his stuff , so don't be SO quick to jump on people trying to help you especially when you don't appear to have a clue as to how that circuit actually works ......

[vortalexfan]

Originally Posted by init4fun

I think ol Levi here could use some schematic reading lessons , the side of the volume control pot at resistor R12 is at B- potential , which is a HELL of a lot closer to "ground" than it is to B+ , that's for sure .

Old coot 88 knows his stuff , so don't be SO quick to jump on people trying to help you especially when you don't appear to have a clue as to how that circuit actually works ......

When I said that I was thinking of an actual chassis ground connection and yes I do know how to read a schematic but like I said, when he said "ground connection" I was thinking he meant a physical chassis ground connection, not B- connection.

Also how would of that ground connection of just suddenly broke when it was working just fine previously?

All I touched in this radio was the capacitors I never touched any of the wiring.

[init4fun]

Originally Posted by vortalexfan

When I said that I was thinking of an actual chassis ground connection and yes I do know how to read a schematic but like I said, when he said "ground connection" I was thinking he meant a physical chassis ground connection, not B- connection.

Also how would of that ground connection of just suddenly broke when it was working just fine previously?

All I touched in this radio was the capacitors I never touched any of the wiring.

Ok , so we've got the "ground" and "B-" thing worked out , great .

Now , just know that while you didn't purposefully touch any wiring that doesn't mean a wire couldn't have got bumped or nudged as you were changing your capacitors . Your best troubleshooting clue that you've given us here is that the volume control worked before you changed the capacitors , that in itself is telling you to check the installation of those new caps very carefully , it's all too easy to make a mistake and sometimes it's not easy to spot a mistake we have ourselves made (a great reason for having at least one electronics savvy friend who might spot something you've missed) ...

[Electronic M]

Some 40s Zeniths would go stone deaf if the wave magnet wasn't connected. Don't forget to connect it for your tests.

[init4fun]

What tube is the parallel caps shown in this picture connected to ? If it's anything "front end" related (RF amp /osc / or mixer) and it's in a grid circuit , the parallel caps may have thrown the circuit out of alignment ?

[vortalexfan]

Originally Posted by init4fun

What tube is the parallel caps shown in this picture connected to ? If it's anything "front end" related (RF amp /osc / or mixer) and it's in a grid circuit , the parallel caps may have thrown the circuit out of alignment ?

those are the coupling cap for the 6V6s (the original was a .05 MFD but the closest I had at the time that I replaced that was 2 .033 MFD caps which I paralleled to make a .06 MFD cap.

So nothing to do with the front end.

[vortalexfan]

Originally Posted by Electronic M

Some 40s Zeniths would go stone deaf if the wave magnet wasn't connected. Don't forget to connect it for your tests.

I know, I double checked to make sure the connection was good between the wavemagnet and the radio chassis and it still seems unresponive.

[vortalexfan]

OK so now I'm getting some static sounds out of the tuner at the spots where the stations would be coming in at but still no audio or reception.

I tried wiggling the tubes you suggested I wiggle (the 6A7 and the 7G7 tube) and it didn't make much difference.

So another question, can having the chassis not being completely tightened down to the cabinet cause reception issues?

[old_coot88]

Originally Posted by vortalexfan

... can having the chassis not being completely tightened down to the cabinet cause reception issues?

Can't think of any reason how/why it should. Question- is there any way the cabinet can be laid on its side, and the chassis slid back far enough to take voltage readings in the RF and IF areas? Or is this a large floor-standing console?

(Back in the day, this was a common accessability practice in TV service, even with console sets. It was usually done with the heavy end of the chassis down.)

[vortalexfan]

Originally Posted by old_coot88

Can't think of any reason how/why it should. Question- is there any way the cabinet can be laid on its side, and the chassis slid back far enough to take voltage readings in the RF and IF areas? Or is this a large floor-standing console?

(Back in the day, this was a common accessability practice in TV service, even with console sets. It was usually done with the heavy end of the chassis down.)

This is a large Phono/Radio Console it's kind of hard to tip it on its side.

[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?