Zenith 10S690 Volume Control Issues

[vortalexfan]

Originally Posted by 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.

OK, thanks! I'll put one in there right away!

[vortalexfan]

I got a .01 MFD put in and its working now!

I'm not really noticing much of a difference in the bass on this radio with the .01 MFD vs. .02 MFD because this thing had really annoyingly low rattley bass previously and I think the .01 has actually toned the bass down to a much more tolerable level so that the speaker isn't rattling my radio's cabinet anymore.

[vortalexfan]

OK well I think it was a little too early to celebrate, because the volume control started acting up again all the sudden, it was working perfectly but then all the sudden the volume got loud and the tone controls quit working again and the volume control is acting like a tone control again, so something must of happened to the capacitor I just stuck in there, which is weird because it was a brand new polypropolene capacitor that was never used so I wouldn't of thought that it would of shorted out or failed open suddenly...

I'm kind of getting tired of having to take this radio apart over and over again just to keep chasing down problems that keep cropping up one after another like this, they really didn't make this radio servicer friendly seeing as you have to go through the front and the back to remove the chassis screws and the knobs on the front are a pain in the butt to remove as well and the preset panel is also a pain to remove.

I can see why they didn't make this particular model of radio for very long.

[old_coot88]

Originally Posted by vortalexfan

...all the sudden the volume got loud and the tone controls quit working again and the volume control is acting like a tone control again...

By "got loud", you mean it went to full volume and you can't turn it down? If so, that suggests the bottom lug of the control has lost its ground connection (or rather its connection to R22).

[vortalexfan]

Originally Posted by old_coot88

By "got loud", you mean it went to full volume and you can't turn it down? If so, that suggests the bottom lug of the control has lost its ground connection (or rather its connection to R22).

No, more like it went to quarter volume and I can't turn the volume down or up anymore because the volume control just acts like a tone control again like it did before when that detector coupling cap was out of the circuit and the tone control pushbuttons aren't functioning anymore excecpt the one marked "normal" (which I'm assuming the "normal" button bypasses the tone control circuit all together).

And like I said it was working fine for about 15 minutes then it suddently quit working again.

I don't know if this is a clue or not as to what may have happened but when I first turned on the radio (after I installed the .01 MFD cap into that spot that was missing the cap for the volume control) there was a smell of melting solder like maybe something might of gotten hot enough to melt some solder, but I'm wondering if something in that detector to volume control coupling circtui got hot enough to melt the solder on that coupling cap I installed and made that capacitor come loose?
If so what would of gotten that hot in that circuit to melt the solder on that capacitor and cause it to come loose?

[old_coot88]

There's nothing associated with that circuit that should draw any current to speak of, let alone enough to melt solder. Anyhow, check for solid continuity (zero ohms) from C11 to where it connects to the IF can, and to the 1 meg resistor (R11).

From the other side of C11, check for continuity to the top lug of the vol control.

There's gotta be an open on one side or the other of C11.

Doubtful, but maybe the cap itself has gone open(?)

[vortalexfan]

Originally Posted by old_coot88

There's nothing associated with that circuit that should draw any current to speak of, let alone enough to melt solder. Anyhow, check for solid continuity (zero ohms) from C11 to where it connects to the IF can, and to the 1 meg resistor (R11).

From the other side of C11, check for continuity to the top lug of the vol control.

There's gotta be an open on one side or the other of C11.

Doubtful, but maybe the cap itself has gone open(?)

Well I kind of lied about that capacitor being unused, (actually it was more like I forgot) it was used as a DC Blocking cap for my Signal Generator, but I wouldn't think that that would cause the capacitor to fail prematurely, if that's actually what happened here...

[vortalexfan]

I have a .047 MFD capacitor, would that be ok in that spot if it turns out that the .01 capacitor did end up going bad?

[old_coot88]

It'd work, but with excessive bass.

But by all means, first check continuity as suggested, from C11 to where it enters the IF can, and to resistor R22. And from the other end of C11 to the top of the vol control.

Measure from right where the leads exit the capacitor body

[vortalexfan]

Originally Posted by old_coot88

It'd work, but with excessive bass.

But by all means, first check continuity as suggested, from C11 to where it enters the IF can, and to resistor R22. And from the other end of C11 to the top of the vol control.

Measure from right where the leads exit the capacitor body

OK so everything checks out, according to what you said it should check out, nothing is measuring open from what I can see anyways.

I don't know if this would cause a problem or not but one of the wires coming out of one of the IF cans has crumbling rubber insulation and it does have some exposed wire although it's not touching anything.

[old_coot88]

Not sure what O.L. means. But if you suspect the capacitor, just parallel your .0033 and .0047. That'll make .008 which will give a tad less bass than the .01. Be sure and test the caps first.

[vortalexfan]

Originally Posted by old_coot88

Not sure what O.L. means. But if you suspect the capacitor, just parallel your .0033 and .0047. That'll make .008 which will give a tad less bass than the .01. Be sure and test the caps first.

O. L. is overload or out of range according to my manual for my digital multimeter.

Going between the side of the capacitor that attaches to the side going into the IF can and R22 I get 2.5 Meg, and then from the same side of the capacitor to the lower volume control lug (B- lug) I get the same reading 2.5 Meg, and then from that side of the cap going to the IF can to the top lug on the volume control I get 0.3 Ohms.

[old_coot88]

Just need to verify solid continuity (zero ohms) as indicated by the red lines in the shetch:

[vortalexfan]

Originally Posted by old_coot88

Just need to verify solid continuity (zero ohms) as indicated by the red lines in the shetch:

Well if you mean using the continuity test to see if it beeps when the test leads touch the connection, then no there isn't any continuity. I traced back to the B- source which was the filter can negative, and I get continuity up until where C13 attaches to R13 after that I don't get a beep from my continuity checker until I get to one side of C11 which gives me continuity between it and the upper Volume control lug.
Which I'm assuming is what you wanted to know.

[old_coot88]

Originally Posted by vortalexfan

... I don't get a beep...until I get to one side of C11 which gives me continuity between it and the upper Volume control lug.

OK good. Now put the checker from the other side of the cap to where the signal lead exits the can. If it's got crumbly insulation, it should be easy to make contact. Or use a pin to stick thru the insulation. The checker should show continuity.

If it does, this suggests C11 is bad. Try the paralleled .0033/.0047 caps for C11.