Most likely the pot has failed, you might need to replace it.
The wiper which is the center pin can grind away the carbon track or just get dirty and looses contact with the track.
Also look for hairline solder cracks around the pins on the PCB.
You could try circuit cleaner spray into the pot but a new pot might be cheaper than the can of spray.  
Phil.

I've not worked on this amp but have worked on similar small amps with some good results with improving tone efficiency.
Assuming I'm reading the right schematic you can raise the value of R14 which is 100k, up to 500k or even higher. (At pin3 of U2A,, after tone stack)
It should open up the tone a little better making it more effective at Boost and Cut.
100k might be loading down the tone section.
Hope it helps, Phil.

Hi Ben welcome
Regards to IMG_4223.1.JPG
My guess is that green wire you mentioned goes to the Chassis.

The idea is to re-route how the ground paths return to the main Common/Ground point,, which is the Chassis. I'm not sure about the 2 dots?

It would be best if you PM "bajaman" as he will be able to explain it to you.

Yes it must be hard when you have to translate.
hope it helps, Phil.

Yes could be the socket but more likely the plug is faulty.
If the speaker cable has a metal shroud then unscrew it and check the connections.
If you have another cable around try that.
Phil.

Although a schematic can help you can still do some testing to work out what has failed.
Maybe give us some more details of what is wrong and folks here maybe able to help.
BTW,,Close up, Clear & well lit pictures can be a big help. (natural sunlight is best) Phil.

Basically you divide it up.
If you have a line out then connect that to another amplifier as that will establish if the preamp is working.
If the preamp is working then you know it's likely the power stage has issues.

If the unit has sat for a long time then insert plugs many times into input sockets as they maybe corroded. you can use WD40 or similar to get them working.
If there is no luck then you will need a DMM to test for voltages inside.
Phil.

Sorry to hear that.
Ok I'm gonna take a stab in the dark and asking better minds to look at this.

Look at J1,J2 & J5 as they are all interconnected to the low voltage rails via R1 & R49 as well as CR32, C54 & C55.

Now IF??? one of those switching circuits inside J1,J2 or J5 was faulty then it could cause a big DC offset. yes/no?

I've never liked those encapsulated plastic sockets as they are rather fragile inside.

My thoughts,,If the input side of C33 was lifted that would completely isolate the power amp input from any interference.

If that resolves the Buzz then I'd hunting down the offending socket,, or just replace all 3.
Phil.

Any lights come on?
You really need to add a bit more info.

Please connect speaker to speaker output,, line out is not for speaker.
Phil.

As mentioned yes check for DC on output but tiss a fair bet that now that the circuit is correct it maybe well be just drawing more idle power.
I would suggest, try a speaker  (with bulb still connected)
If the bulb glows very bright at idle (no signal passing) then there is still an issue.
Phil.

Quote from: joecool85 on May 05, 2022, 03:08:51 PM

Quote from: phatt on May 04, 2022, 08:26:15 PMFor me personally I tend to like Sealed Cabinets for single speaker combos.

Phil.

I was just talking about this with a co-worker.  I believe combos should be open-back, the way God intended.  Just kidding, though I am an open-back believer.

Yes open back delivers a more spatial sound hence fuller effect especially in small spaces but can present weird sonic issues in larger venues.
You may notice that a lot of big pro gigs tend to use closed back cabinets.

A player friend noticed this weird effect at an old wooden school gig where his open back rig was giving him a crossover of out of phase in the position he was limited to in the building. It can mess with your brain and the sonic result can be off putting.

That does not happen as much with a closed back cabinet.
Although it can still effect a closed back cab it is not as bad.
Venues with big Glass windows can have really bad reflections.
Phil.

Speakers are a rabbit hole but a general rule for balance is; If the Amp is dark ,,use a bright speaker.
If the Amp is bright use a dark speaker.

Compare the cost;
You just altered the Amp and it cost you 50cents for a cap.
So even if you have to try several caps to find the right tone it's still only costing pennys.

While speaker swaps may cost you hundreds before you find the right one.
Then there is the Cabinet the speaker is mounted in,, another rabbit hole.

Be warned some of the fancy painted magnets will cost.
For me personally I tend to like Sealed Cabinets for single speaker combos.

Phil.

A whole lot of muckin about that may well cause complications.
As Enzo & G1 have said just unplug the speaker. A lot less work and no chance of stuff-ups.

There is no issue with the speaker unplugged on SS amps ,, Valve Amps Always need a load on the output, while SS amps Do Not.

Hard to read the blur but IC111 looks like a protection circuit,, don't mess with it.

Phil.

Yes it's possible when the power Tr's blew it also effected U1.

U1 is the power stage input, those 4 Pwr Tr's boost the current needed to drive the speaker so both U1 and Pwr tr's could have failed.
The other 2 tr's (Q8 & Q9 I think) are part of the over current protection. 

Now assuming none of the passives or Q8&Q9 are at fault then replacing U1 Should fix the problem.

Hopefully others more qualified will chime in,, if I've missed something.

As you have noted that plugging into the Pwr Amp input still sounds distorted then the Power stage is most likely at fault.

If you want to check if the preamp is working normally then take the Preamp output to another amp (if you have one) if that produces the same Buzz then the problem maybe further up stream in the signal path.
Phil.

Oh dear, Reset,, that noise is not ground hum/buzz that sounds more like a blown poweramp.
I asked if the amp is working and passing signal except for some hum/buzz,, if so you may have a ground issue.

Obviously this is NOT the case.

In your fist post you said you replaced the power transistors but there might still be a problem in the power amp.
My best guess is the opamp at the input of power amp stage might be stuffed.
Check the DC test points on U1. (pin7&4)
Phil.

Good to hear it's worked for you and having the feedback may help others who struggle with these Amps.
A lot of SS Fenders from this era tend to suffer from excess treble response.
Phil.