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Bandit 112

7/15/2004 2:18 PM
Bandit 112
I have a Bandit 112 with this problem:  
(this is a different amp that the one I repaired a few weeks ago)  
pluging in the PA in, ok  
pluging in the efx return, ok (efx level switch works)  
Pluging in the up front, any channel, the amp sounds thin with ugly tinny distortion.  
This amp had (this one too) one of the 15 volt supply zeners blown. All CIs receive the expected current, and there's signal in pins 1 and 7. I see the signal with the scope. Tracing the signal in the clean channel, it is a nice sine wave at VR1 (clean vol pot), and as low power and ugly distortion is present on all channels, I believe the problem must be in or after U1 (analog switch)in the preamp scheme.  
Quite similar problem I had on the other Bandit, shorted 15 volt zener, U6 (switch) and U1A in the PA/efx send-return, bad.  
I'm lost, and ready to change ICs indiscriminately.  
Any help please?
7/15/2004 7:16 PM
Rick Erickson

[QUOTE]pluging in the PA in, ok  
pluging in the efx return, ok (efx level switch works)  
Pluging in the up front, any channel, the amp sounds thin with ugly tinny distortion.[/QUOTE]  
Make sure the return jacks are making a good connection to the send jacks when there is no cable inserted. You can check this by inserting a couple of short cables into both sets of send/ret. jacks to close the loops. If you are replacing IC's install sockets to make life easier. This can aid in future troubleshooting. Good luck.  
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7/16/2004 12:22 AM

A lot of older Peaveys had sockets already.  
You can't scope the input pins of the op amps, but if the signal looks OK before a chip and crappy on its output pins, then change the thing. Those 4558s cost something like 29 cents from Mouser. Parts are cheaper than labor.  
If you had a power supply failure, look at all the pins 1 and 7 on the op amps. Those are the outpit pins, and they ought to have signal but no DC. If there is a DC offset of more than a few millivolts, change the chip.
7/16/2004 1:00 AM

ok, so changing a couple of op amps is not that dishonoring after all...  
I have made a few questions about this amp model but not because they are better or worse than others, it is just that almost all the amps I try to repair come from a place that they hire the room and equipment, and they have Bandits for the guitar and B3s for the bass guitar, that's why.
7/16/2004 5:30 AM
Hey, in the repair biz, you fix what comes to the bench.
7/16/2004 2:19 PM

Got it. Is working now.  
Couple of ICs, and Q9 in the PA send/return section. Thank you!
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