troubleshooting advice for a fender blues deville 4 x 10

[ALBATROS1234]

a friend has the above and has had it in storage because of a problem and asked me to look at it. it was stored in a moist environment as there is water damage /mold spots on the bottom masonite panel of the cabinet. it was making a ton of noise and squealing so i started with the basics, cleaning pots and testing tubes. tubes were tested by comparison to known good tubes side by side in a test amp since i have no tester. so the tubes were all fine from what i can tell.

so what its doing now is the clean clannel seems ok but the drive channel squeals like a banshee if the master is up to 2 or 3 and drive turned to 4ish. this also seems to be affected by the treble control which is also behaving oddly. when turned up the treble control does increase treble but decreases gain , when turned down the opposite happens treble does get cut but, the volume increases slightly and it thickens up sounding fuller. this seems contrary to logic. whats weird is at this moment it seems to be acting ok but this morning when i turn it on plugged into a 15" 8ohm 100w speaker cab i have (because one of the devilles speaker sounds partially blown with a fuzzy ratty tone) only one of the power tubes was lit. that stopped happening upon plugging in amps own speakers .also yesterday i was getting seeming to be high preamp voltage of 260 to 280vdc and now today i am getting closer to 180 on the plates so it seems as if there may be several small issues. i have read that the ribbon cables are notoriously fragil and will almost certainly break on or more connections if you take out the boards so i hesitate and ask advice before i start to disassemble this guy.

i changed v1 to a 12at7 and v2 12au7(which only uses 1 triode in this amp) .this has made the amp playable at loud volume albeit the overall peak volume seems 20 to 30% reduced of its original 60watts. there is still the treble control issue though as described above. and there has been a higher than expected hum. so i thiunk theres a component or 3 bad but what resistors i can test in circuit seem fine so i suspect a capacitor but the treble control does get more trebly when turned up so which cap?

 
basically i was hoping to get advice from anyone with experience with this amp and known problems and/or any of you older pros who may have a clue to  what this could be. i have been fiddling with it for a few days now and have tested voltages in spots which seem sensible for what i would expect to see except when yesterday the preamp voltages were 100vdc higher. any advice apreciated

[shooter]

basic troubleshooting regardless of amp
verify ALL the DC volts ~~~"match" ~~~~ with the schematic
1/2 split, there is a pre out, and PA in jack, makes it easy.

PCB amps are notorious for bad connections, lifted foil, cracked solder, complete visual ,wiggle/jiggle, re-flow

sig/gen scope comes in real handy also, but once it's 1/2 split to an area, shot-gunning parts might work.

[ALBATROS1234]

thank you sir. i did do a basic chopstick tap/push tests on various areas as well as tapping jiggling tubes. did also use contact cleaner on all sockets in addition to pots. my semi educated guess is somehow excess voltage/current is getting into the tone stack, the resistors are marked and all test fine, i guess i could just change the tone stack caps for good measure. if the ribbon cables break i will just have to cut them out and replace them with short lengths of wire which fender should have done originally or at least put a connector on one or both boards so that they dont crack so easily as many techs and owners with blues devilles/deluxes complain about. i will however try to isolate preamp and power amp sections via the effects loop perhaps i can isolate it then. something tells me i have more than 1 small problem

[pompeiisneaks]

I have a fender blues deluxe myself and am about to recap a fender hotrod deluxe.  The electrolytics they put in those are bottom barrel garbage, and are worth changing anyway (I'm of the opinion illinois are great, but the ones fender gets are NOT, the ones Doug sells here are the standard line, not the 'fender asked for the cheapest caps we could produce).  I put in all F&T or Nichicon myself though.  That's another area to consider if it's older and/or as you say been sitting in a harsh environment.  The squeal could be oscillation, though, caused by all the other things mentioned before.  Another area to check would be the 5W resistors in the solid state reverb circuit.  They tend to overheat and burn the board, sometimes destroying the traces.  At a minimum I recommend always removing them and replacing with identical ones, but lift them away from the board, and add in some silicone under them to keep heat away from the board and keep them from vibrating the leads to death that far away from the board.

~Phil

[ALBATROS1234]

thank you for your advice, sounds solid, i gerally use the nichicon power caps i agree and i did see elsewhere about the cheap caps. perhaps if a filter  cap is out on a node of the ps to much voltage could be in that section of the circuit so that is solid advice and will do.