Fender Blues Deville Issues

[52 Bill]

When measuring the preamp tube voltages, it is not enough to simply state the Plate voltage.
You Must include the Cathode voltage.

The 12AX7 plates are pins 1 and 6, the cathodes are pins 3 and 8.

With 400+ volts on the plates, that pretty much tells me that the tubes are not turned on and will not pass signal. Either the filaments are not getting voltage or there is a ground issue at the cathodes.

The filaments are pins 4 & 5 tied together and pin 9. There should be about 6 volts ac from pin 9 to pin 4 or 5.

[g1]

Redo those preamp tube readings with the tubes in. (the pins 52 Bill specified above)

[greenmeanh1]

Farty power amp section solved. R52 100k resistor going to pin 6 of V3 was sort of open. Replaced that and amp is clean and loud through the power amp in jack now. I wanted to solve that before moving on to the pre amp stage. So,
Filaments are all at 6.1 volts ac
I didn't know if the cathodes should be checked on AC or DC range so i did both. No ac volts on V1,V2,V3.
V1 Pin3 1.5 vdc, Pin8 1.4vdc
V2 Pin3 1.4 vdc, pin8 0volts
V3 Pin3 28vdc, Pin8 34vdc.
To me it seems to check out pretty good but i know little.
Im staring at that relay now!! Thinking LOL

[52 Bill]

Didn't read that the earlier readings were without tubes.

V2 Pin3 1.4 vdc, pin8 0volts

V2 Pin 8 seems to be wrong.

[g1]

V2B is unused and pins 6,7, & 8 are tied to ground.

[Enzo]

Is this part ever known to be an issue or blow?

There is no part in any amp that cannot fail or cause problems. ANYTHING can fail.

Having said that, it doesn;t matter whether a part has failed in the past or has yet to have its first failure. ALL that matters is THIS amp NOW. Statistics do not apply to individuals. That other stuff is distractions from the troubleshooting process.

[greenmeanh1]

Thanks for all the replies. I know i am slow at this and i appreciate your patience. I am assuming my cathode readings on V1 and V2 are correct for the most part other than they seem about 2/10s of a volt lower than where they should be so im not seeing this as the problem.
I forgot to mention in my previous comment what my Pin 1 voltages were with the tubes in.
With standby off im getting around 17 volts on V1 and V2
With Standby on im getting 267v on V1 and 271v on V2
I have ruled out the relays because they are switching and there is no difference in output between the two drive settings. Overall volume is still very low but everything seems to function.
So, the only other stuff in between the output of V2 and V3 is the: Master Volume, C9 .22uf 400v cap, R20 330k resistor, the 9pin power amp in jack. Then on the driver input side the is a C14 .033uf cap and R29 220k resistor.
I will start with the 9pin jack i think. Its brand new, i just put it in when i changed all the jacks but i know that NEW means nothing when it comes to those replacement 9pins. First check pins 4/5 and 7/8. Then i will work those caps and resistors mentioned above and report back.
Also power amp in jack works well when signal plugged into it so i guess that rules out C14 and R29

[greenmeanh1]

Found a 30C100k pot in the master volume where it should be a 1 meg 10A!! Could this be an issue?
I discovered that P22 is C14 which is where signal enters the power amp section and that P21 is the master volume from preamp to the 9pin jack. The power amp in jack and the line bussed to P22/ C14 is good.. The master volume to the jack seems to be problematic either in the power amp in jack or the pot. Or maybe the wire itself.
Appreciate further thoughts.

[g1]

Could you restate the problem you are currently dealing with? Is the problem appearing at the preamp out if patched to another power amp? If so, you can rule out anything after it, such as the 'power amp in' jack.

[greenmeanh1]

Currently i have no signal at the preamp out jack. Patching to another amp or to the power amp in results in no signal.
Master Volume seems to not do much of anything when turning it but even at zero there is still a small amount of volume that doesn't change when turning the Master.
A very small amount of signal is getting to the output stage from the preamp.
Also very small signal from reverb pan.
Both guitar in jacks work, the eq works and presence works, input volume and drive controls work.
The Power amp in jack works just fine and is loud and clean.
The footswitch jack switches the drive on/off and the reverb on/off.
My focus is narrowing to the Master Volume control which appears to have been replaced with a 30c200k instead of 1meg10a. Not sure if this is an issue or not but its definitely the wrong part in there. As i said before, turning the Master makes no difference to the signal and stays at about 1 watt all the way through the master volume range.

[TimmyP1955]

The Master volume affects only the Drive channel. Having the wrong value pot would cause a loss of gain, but would not kill it. (A loss of 6dB if I got my math right - which I likely did not.)

The preamp out is fed by one of the TL072 ICs, so you need to figure out if signal is getting there. This does not feed the poweramp section however.

The issue could be one of the relays. Or the switching contacts on the PowerAmp In jack, as the preamp signal goes through one (or more?) of these contacts to get to the poweramp section.

I'd say that you need a signal generator, and an AC volt meter or oscilloscope (preferably the latter).

[g1]

If you have limited equipment (scope etc.), I would suggest removing Q1 (mute Fet) to see if it is killing the signal. For quick & dirty without removing any boards, just cut it off.

[greenmeanh1]

Something is dragging the signal down. There is a series of test points on the schematic i have been attempting to go through. Things start getting weird at TP9 which is pin 1 of V2. Looking for 11.8vac and only getting 4.2vac and slowly rises to around 5.5vac. There is a cap C9 and the next test point TP10 at R20 330k i get 0 on both sides of the resistor when i should have 2.3vac. Same goes for TP11 and TP12 which read 0 where i should have 111m and 106m. R20 reads as a 329k and R22 that goes to op amp reads as 997k. Not sure about C9 .022 400v cap. Wasn't sure how to test it. My thinking was if its open ,it wont pass 11.8vac signal to R20.

[greenmeanh1]

If you have limited equipment (scope etc.), I would suggest removing Q1 (mute Fet) to see if it is killing the signal. For quick & dirty without removing any boards, just cut it off.

That would be the J111. I was trying to understand its function. So it mutes the drive switching noise??or the reverb??

[greenmeanh1]

If you have limited equipment (scope etc.), I would suggest removing Q1 (mute Fet) to see if it is killing the signal. For quick & dirty without removing any boards, just cut it off.

Bold plan!! I started looking at that part of the circuit on a quest to understand what is going on with J111. I found a couple things that were weird. I haven't pulled Q1 J111 yet.
Channel switching voltages check out on U3 as per spec. TP30,TP31 andTP32.
U4 4560 appears to be a problem. I have -14v on pin 7 regardless of footswitch in or out, or on or off so, op amp isn't switching or flipping += TP34. There is power 16v+- to all the op amps including U4 on pins 4and 8.
I also have -14v on pin 2 of the same op amp. TP33. Should be .2v to about 2v max to meet spec. Trace back a little further and R60 which should be a 10k is reading 1.2k. Not sure if this is my problem but i would think with the pedal unplugged from the footswitch jack the reverb should default to on,, meaning Pin one should have a -14v negative output instead of +14,, which means reverb off. So i will put a 10k resistor on the list for R60 and see where that gets me.