The amp in question is a 1980's vintage Peavey Bandit 112 Soloist Series 100W guitar combo and belongs to the singer/rhythm guitarist in my band. Unfortunately at some point between our latest gig and its arrival back at our practice room the control knob for the lead channel level has been snapped off. This is an unfortunate but not too uncommon occurrence which can be attributed to careless handling or bad loading of the van after the gig. On these occasions tiredness / the euphoria after a successful show / overzealous helpers and perhaps a small quantity of alcohol can lead to these sorts of careless mishaps !
So now on to the repair.
Peavey Bandit repair - Step 1: Remove the Amp chassis from the Combo.
IMPORTANT - Before working on the amplifier we double check that it is disconnected from the mains electricity supply ! (ie. Make sure you've unplugged the amp from the wall!)
Next we remove the back of the combo ( undo the 4 screws ) to allow the amp chassis to slide easily out.
Then we undo and remove the power cord retaining clip and unplug the cables that connect to the speaker and the reverb unit (making note of how they need to be reconnected to avoid any errors later on).
Now the combo is laid face down and the 4 screws which attach the amplifier to the speaker housing are removed and the amp chassis is lifted out. All screws are put to one side to avoid misplacing them.
Peavey Bandit repair - Step 2: Remove the circuit board from the amplifier chassis
Next we remove the plastic control knobs from all the potentiometers and remove the black retaining nuts (11 in total)
We also remove the retaining nuts and washers from the 4 input/output jacks on the front panel.
We then unplug the connecting cables which run between the metal housing and the circuit board (4 connectors in total) taking note of the correct positions for reconnecting later.
Once this has been done the 6 black screws which attach the back cover to the amplifier chassis are undone and the circuit board can be slid out.
Peavey Bandit repair - Step 3: Remove the faulty potentiometer.
As can be seen in the photo below the potentiometers are mounted directly on the circuit board and are supported by a small metal bracket which is also soldered to the circuit board. This is so that the circuit board can be assembled as a whole in the factory then easily mounted in the chassis as a single unit.
To remove the pot from the circuit board we carefully desolder the 7 tabs using a soldering iron and a solder sucking pump. The pot can then be lifted off the circuit board.
Once the level pot has been removed from the circuit board we confirm that it is a 10K linear pot.
Peavey Bandit repair - Step 4: Buy a replacement potentiometer.
Unfortunately my local electronics store didn't have the exact replacement part. Normally I'd purchase the original replacement part online if available. But in this case the amplifier needs to be fixed before our next practice session so there isn't time to wait for delivery. This leaves the alternative of buying a standard potentiometer of the same value, size and type and mount it directly on the amplifier chassis with 3 wires connecting it to the circuit board. As can be seen in the photo we also need to cut the shaft down to size. It's a little bit more work but saves waiting, a little money and will be not be noticeable once the amp is reassembled. Obviously we have to use a pot of the same value otherwise the amp's performance will be affected !
Peavey Bandit repair - Step 5: Connect the replacement potentiometer to the circuit board
First we solder three short, insulated wires to the connections on the circuit board. As you can see in the photo I've used different coloured wires to avoid confusion when connecting them to the replacement pot. I've also made sure that the wires aren't overly long , they just need to be long enough so that the pot can be fitted to the amp chassis in such a way that the connecting tags won't touch any other components or the metal chassis itself. I then solder the coloured wires to the corresponding tabs on the pot.
Peavey Bandit repair - Step 6: Mount the Circuit board in the metal amplifier chassis.
This is just the reverse of the removal sequence with one additional stage which is to connect the new potentiometer to the metal housing. Care must be taken to ensure that the pot doesn't turn while the retaining nut is being tightened. The photo below shows how the final repair looks - all neat and tidy on the inside and totally invisible once the amp is reassembled.
Peavey Bandit repair - Step 7: Re-fit the amplifier into the speaker housing.
Once again this is just a case of reversing the removal process, taking care that everything is reconnected correctly.
Peavey Bandit repair - Step 7: Check that everything works OK.
Once everything is back together and we are happy that all the parts are connected as they should be we plug the amp in, connect a guitar (in this case a Fender Telecaster) and make sure that the amp works as before its accident.
