Hot rode deville no sound

[RollingClone]

Ok, I know what I did was the first rule not to do. I installed a mod kit from Fromel BEFORE I listened to the amp. So, I do not know if it ever worked. I trusted my brother, again, and I will never learn. So after the 'quick' mod, I had to bring it back to my shop, and now I am stumped.

I get a very very faint guitar sound, although you can hear a hi-power hum. You play and it sounds like way in the distance, very faint. It is as if the input jacks (part of the mod) are sending to ground. Classic blown 6L6?

However, I do some signal tracing and I hear loud pops in the amp section which tells me it is working. I do have it plugged into the main speaker jack not the ext. I replaced all the 12AX7's, all is well there.

My first problem is, all DC volts are perfect, the AC volts on the schematic are all incorrect. Is there a floating ground used to measure this somewhere? I am using a 100MHZ scope, and a RMS meter. Both don't show what Fender has on the schematic. Is one of the 6L6's bringing everything down to Ground?

So, is 94.3V at TP27 and TP28 correct? Why not write 94.3VAC? I get the DC volts on the tube (461VDC). I understand transfomer theory, I just need to verify the voltages on the fender schematic are correct.

I have checked the solder joints, and while doing that I see there has been much work done to this amp.

Thanks.

I have tripled check the wiring of the input jacks.

Tube checker has passed all the tubes as well.

[MWJB]

Oval figures are AC, figures in rectangles are dc.

94.3VAC seems right enough.

All dc voltages are OK...please double check, especially both plates of V3 (pins 1 & 6) and both 6L6 screen grids (pin 4).

Try the 6L6s one at a time, in both tube sockets, to see if a blown tube is the culprit. Better still try a new pair (known to be good).

At which point, from the input, do your voltages begin to differ from the schem? Confirm that you have bright switch out reverb fully off, all other controls set to 50% rotation, drive channel selected?

[RollingClone]

I have the correct channel, and I have checked the tubes. The sound is so small you barley hear the guitar, however you hear a loud hum. Also loud pops as I trace through the amp section.

Ovals being AC, I get that. However, they are all wrong when I check them in the amp. I was thinking maybe there was a floating reference, even though the print says to ground.

If these AC test points are out, all of them, what could it be? Transformer?

Thanks again

[MWJB]

It would only be the output transformer if that's where the signal dies. But if you get low AC at TP2 (<196mV) then the problem is at the input, as you say "all AC voltages are wrong", then you need to start at the input and see where they start to die off.

[52 Bill]

To me it sounds like a break in the signal path.

Try plugging your guitar into the return or power amp in jack. If you get a good signal there, work forward from there. For that matter have you tried jumpering the loop jacks with a spare cord?

Look for open caps, resistors or bad pc board traces.

[RollingClone]

OK, so plugging into power amp in works.

So, go back from there.

[RollingClone]

I found some cut solder runs on the first preamp. Something I have not seen since a lab at school over 20 years ago. In any event. I repaired them and now it is louder, but still very weak.

I suppose I should keep tracing runs and look for shorts or opens.

However, it seems the volume pot has no effect, and it reads fine on the meter.

I need to get another signal generator.

All tubes matched in the tube checker, plus I have replaced with known good ones. The 6L6's are of different manufacturer, but, both stamped 6L6 GC.

[52 Bill]

I suppose I should keep tracing runs and look for shorts or opens.

And for open coupling caps or broken resistors.