Repairing a Peavey Bandit 112 Guitar Amp

Today were going to look at a fairly common and easily performed amplifier repair.

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.

Fixing up a cheap electric guitar so it plays like a more expensive one !

A friend of mine called me up last week to ask if I’d take a look at a guitar for him. Apparently his girlfriend had bought him a cheap Stratocaster copy online for his birthday but the guitar was totally unplayable. He was pretty stressed because he didn’t want to tell his girlfriend that she’d wasted her money!!

To be honest I was surprised how bad the guitar was! I understand that it was very cheap, but it was truly unplayable. I was especially surprised since it is a Yamaha guitar, albeit their most budget model. I’ve played several Yamaha guitars over the years and they’ve always been good instruments. In fact I have an old Yamaha Pacifica as a reserve electric guitar. Actually this guitar was so bad that I suspect that is probably a factory second or a knock –off copy or such being sold online by an unscrupulous dealer.

Whatever, in the end it only took a couple of hours work to get it playing pretty well (in fact once I’d finished with it I had it pretty much set up to the same specs that Fender set their guitars up to when they leave their factory !) Anyway, here’s how we fixed her up.

First of all I tuned the guitar to pitch and tried to play her. Terrible, even with the strings set pretty high from the fret-board it buzzed and rattled and at some frets totally fretted out.

My first step was to try and straighten the neck using the truss-rod. I was pleasantly surprised to find that the truss-rod worked and that I could get the neck almost totaly straight under string tension. In fact you never really want a totally straight neck on a guitar, a slight relief is necessary to allow for the curve of the vibrating string. Most importantly, the neck wasn't twisted ( a twisted neck can often be fixed , but its a lot more work).

So now with the neck acceptably straight I proceeded to check the frets to see if they were level. A quick check with my Stew Mac fret gauge showed that the frets had never been levelled or dressed in the factory. (Note: This is hardly a surprise with such a cheap guitar; even fairly expensive guitars need to be taken to a Luthier to have the frets dressed if they are to play at their best.) It also showed up the reason why the guitar was unplayable: Frets 2 and 19 where ridiculously high, to the extent that I thought that maybe they weren’t correctly seated, they where. Actually I suspect that the other frets had been inserted with too much pressure and for some reason these 2 frets had stayed high.

This photo shows how we check the frets for level, we test 3 frets at a time - if the middle fret is high then the guage rocks, if not it stays firm. Please note that this photo is taken on a different guitar and with the strings removed.

Step 1 – Level the frets.



Since this guitar ( as is the case with most Stratocaster copies) has a screw on neck. The first thing to do is remove the neck (actually the first step is to remove the strings then the neck). Next we remove the plastic nut and re-straighten the neck sighting down the fingerboard with a straight edge. (Note: we want the neck as straight as possible at this stage). Guitar fret-boards are normally made of a hardwood like maple, rosewood or ebony. In this case I noticed that the fret-board was made of a softer wood dyed black to look like ebony. This is probably why the frets were so bad.

Once the neck is removed and straight I tape off the fingerboard with masking tape to protect it while I level the frets. Many luthiers use a metal file mounted on a wooden handle like the one in the photo below to do this. I find I get better results more quickly using a metal spirit level with sandpaper stuck to it. This has the advantage that it is almost as long as the guitar neck so it helps prevent you from sanding more in one place.

First I concentrate on numbers 2 and 19 (always working in the direction of the strings line and checking for level and profile) to quickly bring the two high frets down. Once the 2 rogue frets are about the right height I ink up all the frets with a marker pen and then work very carefully to maintain the correct profile. If you work carefully you should just need to keep sanding until the ink has just started to be removed from the lowest fret . At this point all the frets should be at the same height. We check with the straight edge, until we are totally happy that the frets are levelled.



Step 2 – Re profile the frets



Guitar frets are a half moon section. But the levelling process will have caused them to be flattened off. Flat frets rattle and play out of tune. So the next step is to round the frets off using a special small file with a rounded face (see photo). Whilst doing this you should keep checking that you maintain the correct fret-board radius using the plastic radius gauges (mine came off e-bay). Once the frets have been rounded off you should polish them up using different grades of emery cloth, wire wool and finally metal polish.





Step 3 – Neck back on



Once we’re happy with the fret job, we remove the masking tape, replace the nut and bolt the neck back on to the guitar. At this step I check the neck angle using the straight edge and find that it’s not as it should be. This is easy to fix on this type of guitar using card shims in the neck joint.



Step 4 – Final setup



Next we string the guitar up with a new set of strings ( I prefer ernie ball 10 guage) and bring them up to pitch. She’s already starting to play better, no buzzing or choking strings. But the action is still high, so we adjust the neck relief with the truss rod and the individual saddle heights using Allen keys.



Step 5 – Play and enjoy



Considering how cheap this guitar was, I was very pleased with how it played once we’d fixed it up. If the guitar were mine I’d probably have made a new nut for it too which would have seen yet more improvement.