Bandit 112 reverb fix

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Bud977
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Bandit 112 reverb fix

Post by Bud977 » Sun Nov 14, 2021 3:07 am

I just bought a teal stripe Peavey Bandit 112. It's my first non-modelling amp and I'm impressed. Great sound and a lot of adjustment even without pedals.

The only thing not working is the reverb. As you turn up the dial, an annoying electrical hum and physical resonance of the reverb tank increases until the dial gets to 4. Then there is an electrical click and the noise drops back to a static crackle which stays at the same volume all the way to 10.

I've cleaned the reverb pot with Onyx which made no difference. There is no visual fault in the tank or the top of the circuit board.

This is my first go at having a play inside an amp. What should I check next?

I jumped in the deep end and also bought a Special 112, which came with the OEM footswitch, and an Envoy 110. All are USA made. Both of these need some attention as well so hopefully I'll be on a good learning curve with these.

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Pappy B
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Re: Bandit 112 reverb fix

Post by Pappy B » Sun Nov 14, 2021 10:01 am

If you didn't do it already, pull the molex connector where it goes into the bottom of the chassis and clean the pins and sockets. Pull the rca plugs at the pan and make sure they are clean. Those areas can really corrode up over the years. Also make sure you have the cables in the right jacks on the pan. If they have been swapped it will not work.

One other possibility is the IC chip has gone bad. Or some one has pulled it and put it in backwards.
The more I learn the more I realize how much I don't know.

Bud977
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Re: Bandit 112 reverb fix

Post by Bud977 » Mon Nov 15, 2021 2:34 pm

Tks Pappy. I cleaned up the reverb plug, and swapped out the reverb unit with the working one from my Special 112. The problem still remains. So it must be a problem in the board. I'll have to pull it out and see what I can find.

Can a Mechanical Engineer solve an electronics problem? Never done it before but I'll give it a go.

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Pappy B
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Re: Bandit 112 reverb fix

Post by Pappy B » Mon Nov 15, 2021 8:11 pm

If you don't find it on your own there are plenty of smart people on this forum that can get you through it.

I some times view electrical problems as hydraulics. Voltage - pressure, current - flow and other components as restrictions, valves, or manipulators. Once I got over the fear of screwing it up I realized I enjoyed working on solid state stuff even though I don't always know the theory.

I would take a look at the IC chip that is in the socket closest to the in and out molex connector. You don't have to pull the circuit board out to do this. It's probably an 4558 or 4560. If the legs look black or dark gently pull the chip straight up then use your deoxy spray and clean up the legs and socket. Even if it's not the problem it's good maintenance. Or better yet.pull one out of another amp that you is good and try it. Just go easy, the little legs bend easy, and get it oriented right. You can look at the other chips and their sockets. The sockets have a notch in one end, the chips have a dot (or a number 1) on top. The dot goes to the notched end.
The more I learn the more I realize how much I don't know.

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JamesPaul
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Re: Bandit 112 reverb fix

Post by JamesPaul » Mon Nov 15, 2021 10:46 pm

Bud977 wrote:
Mon Nov 15, 2021 2:34 pm
...

Can a Mechanical Engineer solve an electronics problem? Never done it before but I'll give it a go.
A side note, but yes a Mechanical Engineer can be quite good with electronics. Tom Scholz, who created the Rockman and the effects branded under the Rockman name, had degrees in Mechanical Engineering. :)
Enzo wrote:I find if the amp is working, that is a good point to stop fixing it.
James Paul's Peaveys
Decade, Classics, Ecoustic, Windsors, VYPYR, Triple XXX, XXL, VKs, Bandit, JSXs, VIP, Piranha and a Penta.

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Enzo
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Re: Bandit 112 reverb fix

Post by Enzo » Tue Nov 16, 2021 12:25 am

Troubleshooting is troubleshooting, a universal skill. The technology involved is only a detail.

Beach
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Re: Bandit 112 reverb fix

Post by Beach » Tue Nov 23, 2021 10:09 am

Turn the amp on. Now hit the reverb tank (gently) with the back of a screwdriver or so. Do you hear ''boinggggggg' ? If yes it is probably the driver circuit if not the fault is in the end circuit (behind the reverb tank). When you do not hear the 'boooinngg' It could be as simple as the reverb footswitch jack that is greasy or rusty. Does it work with the footswitch?

Bud977
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Re: Bandit 112 reverb fix

Post by Bud977 » Fri Nov 26, 2021 5:25 pm

Hi all, thanks for your encouragement. I've tried a couple of things with no success.

I pulled the 4558 chip for the reverb and swapped it for the same one elsewhere on the board. At the same time, I cleaned around the reverb cable pins on the board as there looked to be some muck which may have been bridging between the terminals.

Switched it on and while there was less hissing, the main problem still exists. Swapped the chips back and still the same.

Pulled the board and had a look. Nothing apparent to my eye.

Hit the reverb tank with a screwdriver as suggested. No noise. Doesn't work with the footswitch.

So the problem still shows up as when I turn the reverb knob up, a high buzz and a low humm appear and increase as you turn the knob up to around 4, then past that it clicks and the sound changes to a squelch at a constant volume all the way up to 10.

I looked at the circuit diagram, ut making sense of that is beyond me at the moment.

What should I test next?

BTW, I serviced my other newly acquired Peaveys (Envoy 110 and 112 Special) and have got both of them humming. That 112 Special is a beast. Awesome!

Beach
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Re: Bandit 112 reverb fix

Post by Beach » Sat Nov 27, 2021 6:29 am

It cannot be difficult, do you have any measurement equipment and the schematic?
What happens if you disconnect the reverbtank (first try only disconnecting the input, than output).

Bud977
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Re: Bandit 112 reverb fix

Post by Bud977 » Mon Dec 20, 2021 2:32 pm

All fixed. I took it to my guitar tech and he found a problem with the pins on the reverb molex connector. Bad connection with the board. It's working perfectly now so I'll be taking to a jam tomorrow.

Now I've ended up with a bunch of perfectly working Peaveys. Should I cut down? I've now got a Vypyr 1, Vypyr 3, Sanpera 2 pedal, Envoy 110, Bandit 112 and a Special 112. Funny how they just multiply.

Actually, I just gave the Vypyr 1 to my daughter, who has recently moved out of home, to use as a practice bass amp to use in her bedroom. So that's one less taking up space.

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