Advice on fixing my Fender Amp. Has Shrill sound

[VGuitarist]

Greetings Everyone,

I have an old Fender Deluxe 112 Plus solid state amp (type: PR291, Serial: LO-674886). Been sitting in the garage for a few years. Want to give it to my son, a 9 year old aspiring rock and roll guitarist. It used to sound good, but now the sound is mostly midrange/treble. I do hear some low end if I crank the bass knob all the way up. The shrill sound goes to the bone!

Don't want to toss the amp and could use some help locating the root cause. I already inspected the circuit board and did not see any burnt components. I also re-soldered every connection...no help. I'm thinking the next move is verifying capacitor values (non are physically expanded or leaking). Any other advice? I'm an engineer, so electronic-speak is not a problem.

Does anyone have a schematic for the amp?

Thanks in advance!

VGuitarist

[Enzo]

Don't try to check every part, your meter doesn;t put real world stress on them anyway.

Isolate the problem.

You have preamp out and power amp in jacks, so plug the guitar into the power amp in.  Sound the same or is that strong and clear?   Likewise, feed the preamp out to some other amp and speaker, and play guitar into the normal input.  Now does the preamp sound OK coming out the othyer amp or does it have the problem?

Speaker could be binding, connect the amp to a different speaker, any change?  Does it sound this way in headphones, I see a headphones jack.

[VGuitarist]

Makes sense. I'll post the results later today.

-VGuitarist

[VGuitarist]

Had a minute, so I cross connected another Fender amp with it (pre-amp to power amp). Definitely the pre-amp. Sounds reasonably good from the second amp pre-amp out --> bad amp power amp in. The opposite direction produces the same shrill sound on the second amp. Any thoughts before I begin component level troubleshooting? I found the schematic.

Thx

-VGuitarist

[phatt]

I don't know the Amp in question but if you suspect preamp,,
I'd look at the tone section,, maybe a pot has gone open.
Phil.

[J M Fahey]

Since the power amp checks fine, you can use it as a sound tracer to check the preamp, step by step, but we need the schematic posted here so we can all talk the same and suggest tests.

[Roly]

I found the schematic.

So post it here so we are all on the same page.

[g1]

schematic:

[VGuitarist]

Thanks g1. More noteworthy info: the left volume POT (input 1) bleeds audio when the amp is turned all the way down. I replaced all pots with Fender originals about 6 years ago. It worked fine then.

-VGuitarist.

[g1]

  You should probably start by cleaning all the pots.  Dirt/oxidization could cause the tone control issues and the volume bleed issue.