Super-sonic 22 preamp acting funny..

[Telekaaster]

Dear ampaholics!
Freshman needs help...

I'm a newbie at this great forum as well as a novice in amp repairs, been building guitars for a while and figured I'd try to expand my knowledge.Been building a couple of kits, and reading up on everything I find around here and elsewhere.
The issue at hand is within my beloved Super-sonic 22.
The problem arose one day the poor thing was left on(with tiltback legs to thorughly accumulate the heat) for about 8 hours straight. Something got toasted, but what?

When I turn it on, everything is normal, but as the amp gets nice and warm, the clean volume and tonestack is kinda bypassed. No pop or noise when it happens. The volume freeze at about 4 o'clock, pot not responding and the sound get harsh and brittle due to the nonfunctioning tone pots..
The Burn channel is seemingly unaffected.

I've been concentrating on the first gain stage, swapping v1 gave no result. I changed the volume pot, took out and checked most of the resistors in the area that could be suspicious, While at it, I changed C3 and C7 as a mod I was gonna do anyway, but with no result.
I've been looking all over for bad solderjoints, with eyes and meter, but haven't found anything. Have not resoldered the zillion points yet.
Could one of the relays cause this?
A cap?
Could V2 have anything to do with this as a part of the Fat circuit? I will swap and try that today..

I'm on an Ipad and haven't got a clue how to upload the schematics, but it is allready on the forum somewhere. I'll upload it as soon as I get on the computer...

Any inputs on this is greatly appreciated, got a gig on friday....


Also, I have no signal generator to check signal flow, any diy tricks on this?


Regards
G.Kaas

[Jazz P Bass]

Is there a schematic to be had?

Belay that last one.

http://support.fender.com/schematics..._schematic.pdf

[Telekaaster]

Thanks, Jazz P Bass.

I been fumbling around in the tonestack and v1a suspecting the signal to bypass it, but the issue might be more complicated.
I just fired it up again to see if changing V2 does any good.

Thank you for showing interest
G

[Mick Bailey]

What happens when you turn the clean volume pot to zero? Does it kill the sound?

Both the burn and vintage signals converge at V1b - the only difference is that (up to this point) in 'Burn' mode the clean volume and tone stack are bypassed. If only the clean volume and tone controls are affected I'm thinking your fault lies in that section of the circuit - between V1a and V1b. If the volume control will go to zero I'd suspect your clean treble pot has a connection problem on the lower (anticlockwise) leg - check the solder joint if so.

[Telekaaster]

Hi, Mick
None of the three pots respond at all when the channel "locks"...
I'm heating up the amp now. It usually occurs after 30-60 min.
It makes sense with the treble pot, will check.

[Mick Bailey]

When you say the three pots, what about the volume pot?

Edit: Ah, just seen there are only three pots - no mid control.

[Telekaaster]

Mick,
You are on to it I'm sure. It did not happen yet, making changing V2 a possible fix..
BUT when I jerk around the treble, it makes nasty noise when cranked.
I will shut down, take the pot out and check it.

[Mick Bailey]

Usually when an FMV tone stack goes 'thin' and loses control, either the treble pot leg has lifted, or the slope resistor (R8, 100k on this amp) goes open or has a bad joint. The volume control will have a reduced effect in this case, as it can only act on the treble frequencies, but will still turn down to zero.

[Telekaaster]

Whoaa, Mick!
Did it, took it out(they may snap IN, out is a different story...) It measured good. Back inside pot is quiet. No crackling when wiggled. I'll give it the test of time, but this smells of victory!
Big love, thanks and respect from this side of the pond!!
Terrific, this forum

[Jazz P Bass]

"they may snap IN, Out is a different story...) "
True enough.
Thanks, I needed a chuckle.

[Telekaaster]

The plot thickens. None of the above actions fixed it, after all.... I was pretty sure of success after the treble control was brought to silence, but alas...

The case is still this: after half an hour or so of playing, the clean channel "locks". None of the knobs on ch 1 responds. That would be Bass, Treble and Vol. The bassman/deluxe switch does not respond either.... The tonestack seem to be bypassed and the volume now resembles about 4 in normal operation. A good bit louder than I usually keep it.

My suspect is now the voiceswitch, but I must admit I'm clutching straws here....
Mick, still on?
Any help on the matter is greatly apreciated.

[52 Bill]

A bit more information might help. When the amp locks up, does changing any of the other controls like the dist channel gain control have any effect on the sound?

[Enzo]

Don't guess at parts, and don't randomly change parts. I doubt it even is a part.

Your volume control stops working as do the tone stack. That says to me the ground connections to those controls is opening. There could be a cracked solder connection, there could be a broken copper trace. But on many Fender amps - I don't know in this case - they use the little support brackets on the controls as ground conductors, one ground path flows control to control through the brackets.

Clip your ohm meter to ground, and let the amp run. When it freezes up, quick measure resistance to each pot bracket - while it is running - to see if they all remain grounded. It may not be convenient to get at the grounded lug of the volume pot, but R11 is the mids resistor in the tone stack, and it ought to be easier to get on. See if it is losing its ground connection.

[Telekaaster]

Hi, Enzo! Thanks for the advice on erratic parts changing. I've certainly done my share on this amp with nada results.
As of writing this the amp is in "normal mode". Some hours ago, it slipped into the lock, sadly before I read your input. Anyway, I poked suspected solder joints with my chopstick looking for the bad apple, but no reaction..

I sat back to study the schematics for the umphtieth time, and after a few min the channel suddenly slipped back to normal.

So now I'm sitting here waiting for the channel to lock with a silly riff on my looper pedal.
To narrow the search for the probable ground lift, here's what I have done so far in this mad hunt:

-My first assumption was a bad volume pot, so I replaced it with a new one. These are the SnapIn type.
-The treble pot had some scratch. I took it out, blew it clean, measured it and put it back.
-Lifted and measured R8, R7, R11 because of seemingly dodgy solder joints.
-While at it and as part of a mod to mainly bring the normal and fat mode on the voice switching closer in volume I replaced C3 and C7.

None of wich did any fix, but it must mean that those connections are healthy? BTW the bass pot connections looks impeccable.

There seems to be no way to force the behaviour to occur. Not with turning the pots, switching the mode, poking, joints and putting towels on it to raise the heat anyway......
So I'm sitting ready with my meter in the night to take them readings, as soon as that devious construction decides to go loco again.

[Enzo]

Remember those support wings on each pot. That is four feet soldered in. Those brackets carry ground across teh front of the amp board, so make sure ALL those connections are good, hell, just resolder them.