Hi LB, and welcome, 
If the Channel led indicators are not working then the issue may well be in the switching circuit, (RL1 at top of drawing)
The relay contacts maybe faulty or power not going to B (the 1k5 1W resistor)..
 Should be over 50VDC at B. Then at the relay should be 12VDC controlled by the 12V Zener.
Oh and your sand box resistors are fine, that is just the filler crumbling nothing to worry about.
HTH, Phil.

I'm assuming you are using this for el guitar? If so then the lack of bottom end is likely due to the presence of the horns producing so much treble it drowns out the Bass.

If you are chasing the sweeter tones that good guitar rigs produce then the last thing you want is hi Freq horns.

Also if the amp has a Scorpion speaker they are already very bright when compared to other famous guitar speakers.

Should be easy enough to disconnect the horn and see if that sounds sweeter and improves the low end.
Phil.

Yep this confused me years back, 2u2 would be 2.2uF

I did read somewhere that the point can be easy missed in drawings and after many photo copies and creases in the paper it may look like 22uF.
Same goes for R's 2k2 = 2.2k.
HTHelps, Phil.

I would consider Main Caps draining in a few seconds Normal.
Likely some will take longer.
Valve Amps, Yes they can hold a charge for much longer.

Regards the pots position,, maybe the pots have been changed in a repair job. Lin to Log swap will make that happen.
Phil.

Is there any particular reason why you want to replace the Capacitors?
If the Amp works fine don't mess with it.
Phil.

Ok easy stuff first,
I don't know the amp but from pictures the amp has 2 effects loops, one front the other on the back.
Just bridge them both with a couple of spare guitar cords.

If that fixes the issue then one of those FX loops has a failing contact switch.

FX loop failure is a VERY common issue as the sockets are often cheap crap.

If you want to save yourself a whole lot of work just get a couple of stumpy jumper leads and leave them plugged in.

If it's still not working then you look deeper.
HTH, Phil.

I think one needs to realise that the sound/tone/feel you hear are **Recordings** of a rig that has been tweaked in the studio.
There would have been a lot of post FX on the mix down. Modulations, Reverb reflections added to it.
Many people forget this fact and hence you can go in circles trying to replicate a sound/tone.
Trying to replicate a recording with any basic preamp is just not going to make the cut.

The raw sound of the Amp used may well sound very, shall I say Bland and somewhat lifeless.
Phil.

Hi wim, first up, Does the Amp work as per normal?
For that era the Foot switch is likely a latching type.
Use what you have or use an open plug and bridge the terminals you will soon work out if it's latching or not.
I have no idea about the flying resistor, hard to tell what it's connected to??
As for the Caps padding, Yes often done when they run out of parts.
As I've never seen these amps, looks like it's a budget brand so could be factory layout.
(I've seen worse from Early Roland amps)

Re Speaker issue,, why not use the original spades?

80Watts clean from 130 Watt rig is par for most gear,, Sand or Glass

Phil.

Welcome to the crazy forum,  
One of the springs may have broken off. You will need to open it up and have a look. Maybe post some pics of what you find inside the tank.
Phil.

Before you assume the amp has a problem, Try another guitar and another guitar lead just to rule out the obvious stuff.
Phil.

Most of the magic you hear is most likely created in the power stage ,,,so highly likely if you mess up that you will regret.

you have negative Feedback connecting the output back to those 2 transistors so there is a lot to consider before you mess with that section,,, as I said you need to fully understand before you mess it up. If you blow that OTx you will struggle to find a replacement Rendering it land fill.

I'd advise you to check out simple Non invasive options.
Google L pads, or add a fixed resistive divider at Spk output.
Or try to find a less efficient speaker.
Phil.

No no no,
         Those 2 transistors are DC coupled they work as one, as the amp seems to be working after removing the mod then consider yourself very lucky.

Research a small attentuator on the speaker output or throw a heavy blanket over the speaker but never interfere with the power section unless you know exactly what you are doing.
Phil.

Yes RL is a resistor. RL is the left over from my simulation drawing. (It's R9 on the PCB)
I think it's mainly there as a discharge path, as long as it's high enough to not load down the signal then it's fine.
Phil.

Hi Joe,
         Well after some digging into old CD's I did find this which may help you.
A screen shot of PCB layout for Version4, the one I made for my Pedal board.
If you want it to fit onto a standard pedal case then you will have rethink the layout as you can only fit 3 16mm pots side by side in a Boss size pedal case.

You can reduce the slope R1 for say 56k will give a little more bottom end but 68k seems to be about right to my ears.
As mine is on all the time I just used a simple flick switch instead of a stomp Switch. As there is enough info on the net for bypassing and battery setup I've left all that out of the Schematic.
Note;
 The Protection Diode (Orange) is in the wrong place on this layout, it should be in series before the resistor.
Also R000 is just a wire link.

I still have never been able to perfect KiCad it's a bit of a pain to work with but it was free and board size was not limited like Eagle so I persevered with Kicad.
Sadly now my Eyes are letting me down and I don't do much work on circuits but I still try to fix stuff for other muso's if it's not too fiddly.
Have fun with it. Cheers, Phil.
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Hi Joe,
        Sadly no as that hard drive died and took with it a lot of stuff. I do have some pcb pictures on CD somewhere but they are the early versions which were hand drawn and the early circuits are different.
It's not a hard circuit to layout as there are not many parts and only one chip.
Someone on another forum posted a perfboard layout of it, just let me know if you go in that direction and I'll post it.
Phil.