Peavey Bandit 65 troubleshooting

Discussion in 'Shock Brother's DIY Amps' started by LowCaster, Feb 11, 2020.

  1. LowCaster

    LowCaster Tele-Afflicted

    Age:
    47
    Posts:
    1,071
    Joined:
    Jan 24, 2011
    Location:
    Paris, France
    My old Bandit 65 solo series is suffering from intermittent breakdown.

    I can play it loud, clear, or on the drive channel, and with reverb, everything sounds ok, but randomly it stops making any sound. Sometimes after unplugging the guitar or turning it off and on it will resume normal operation immediately, sometimes it will not work until a few days later. I’d like to be more specific.

    13B5D331-8931-4297-A30F-DB4BCF7BFA8E.jpeg

    F1B69253-489A-479B-B26D-647A84B53D4F.jpeg

    What I already did:
    -replaced the effects loop in and out jacks.
    -soldered the wires directly to the speaker connectors.
    -used contact cleaner for the pots

    What I found today after a closer inspection: one cap is not looking good. That’s C6 the purple 0.47uF /50 On the following pic.

    45C8DD82-FF5C-4AE3-A8EF-64344C4CE710.jpeg


    So the plan is to replace all the electrolytics, big and small.

    Everything else looks good to me. I was suspicious about the thermal breaker that is between the two big transistors in the second pic, but I don’t see any sign of problem here.

    What is your advice? What else should I look for or replace anyway?
     
  2. jvin248

    jvin248 Poster Extraordinaire

    Posts:
    8,677
    Joined:
    Apr 18, 2014
    Location:
    Lions & Tigers oh Mi !
    .

    Symptoms of heat or vibration issue.

    Clean the jacks you didn't replace. Check the guitar cable. Clean the pots.

    I would start with 'chop sticking' it. Wood chopstick to tap on the various parts while on. Like the ceramic power resistors and the two big caps. Basically anything that gets soldered and has a mass that can vibrate and break solder joints.

    Can you feel heat radiating off any parts? Discolored/burned areas? Something that looks cooked? Burning smell? focus on that part or any around it.

    When it cuts out, can you measure where there is voltage in the circuit and where there is not voltage in the circuit? Find out where the kink in the garden hose is stopping the flow.

    .
     
    LowCaster and sds1 like this.
  3. sds1

    sds1 Tele-Afflicted

    Age:
    43
    Posts:
    1,178
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    With intermittent operation like this, I (too) start to think about heat or vibration-induced issues.

    Are you able to reproduce on the bench?

    If you could play it thru another cabinet for a while, I mean this is non-scientific AF but it might at least help lead you to ruling out vibrations shaking something loose.

    Guessing, shotgunning parts is a real crapshoot here as until you can narrow it down a bit, the entire amp is suspect. I'd hold off on the electrolytics and collect whatever add'l diagnostics you can.
     
  4. MrCairo46

    MrCairo46 Friend of Leo's

    Posts:
    2,774
    Joined:
    Jul 17, 2009
    Location:
    Baltimore, Maryland Hon!
    It’s the jacks.
    The input jacks are all mounted on the main circuit board and over the years micro cracks have caused bad soldier joints. Touch them up to reset set them with a hot iron.
    Another fix is to plug a patch cable into the effects loop, in, into out.
     
    Paul-T and rangercaster like this.
  5. LowCaster

    LowCaster Tele-Afflicted

    Age:
    47
    Posts:
    1,071
    Joined:
    Jan 24, 2011
    Location:
    Paris, France
    Thanks!
    I’ll tap the parts, and try to check the voltages when it cuts out. If it cuts out! It seems to always do the contrary of what I want.

    The input jacks are not mounted on the PCB on this amp, they are good old switchcraft jacks, but I’ll inspect them.
    I replaced the effects loop and tried the patch cable trick before with no success. It seems to be the usual suspect for any failure of the Bandit.
     
  6. MrCairo46

    MrCairo46 Friend of Leo's

    Posts:
    2,774
    Joined:
    Jul 17, 2009
    Location:
    Baltimore, Maryland Hon!
    Hhmmm then good cleaning might be enough
    Good luck
     
  7. LowCaster

    LowCaster Tele-Afflicted

    Age:
    47
    Posts:
    1,071
    Joined:
    Jan 24, 2011
    Location:
    Paris, France
    Actually the more I work on it, the better it works, so you might be true.

    The amp was in the quiet state when I started measuring voltages, then I hit one leg of the power stage transistors (Q8, the one that is just before the big transistor) with the probe and got a loud pop. Since then, it is working perfectly so I can’t find anything usefull. o_O

    Chopsticking didn’t do anything.

    Then I decided to clean all the jacks again, check every screw and connectors. And I put the amp back together and will play it and see if it is better.
     
  8. mexicanyella

    mexicanyella Tele-Afflicted

    Posts:
    1,319
    Joined:
    Jan 26, 2012
    Location:
    Troy, MO
    In the first gut shot I see at least two white plastic “molex” connectors plugged onto pin contacts on the board. Oxidation or dust on the contacts of those will cause Peavey screwiness. Unplug, spray cleaner on contacts, plug/unplug a few times. Do the contacts remain tight and springy?

    Bought an old CS400 power amp once with a dead channel. It was just dirty molex connectors and jacks.
     
  9. hopdybob

    hopdybob Tele-Afflicted

    Posts:
    1,332
    Joined:
    May 28, 2008
    Location:
    netherlands
    i don't know if it is with this model to, but i read somewhere that the board is very close to the mounting etc of the transformer that created a short with one user.
    my express 112 i have changed all the power caps you have on the left second picture.
    maybe this helps
     
  10. LowCaster

    LowCaster Tele-Afflicted

    Age:
    47
    Posts:
    1,071
    Joined:
    Jan 24, 2011
    Location:
    Paris, France
    Thanks, that was part of my « cleaning » process, and they work well, or so it seems. But it is worth mentioning because they are one of the few weak points in this amp.

    The two connectors on the right are for input jacks and effects loop and footswitch. The wires are pinched (not soldered) in the mobile part of the connector. I can imagine a benefit from soldering those wires directly to the PCB, in the future. There is a connector from the transformer on the other end of the board, and one for the reverb tank on the underside.

    I’ll investigate next time, if the problem is still there.
    Caps replacement due in the near future.
     
  11. Westside

    Westside TDPRI Member

    Posts:
    13
    Joined:
    Mar 16, 2010
    Location:
    Chicago
    I have a Bandit 65. I started getting intermittent dropouts and occasional noise. I eventually figured out that it was the connector for the foot switch. At the amp end, the cable fits into a multi-pole connector. The fit between the connector and the plug was not good, and the channel switching was operating randomly. I tried to adjust it, but I finally wound up replacing the connector and cable entirely with an industrial multi-pole connector. Now it works fine. Not sure if that will help you but it's easy to overlook that connection, especially if you have the amp on the bench and the footswitch is not plugged in. On the other hand, if you are having the problem even with the footswitch removed, then that's not the problem.
     
  12. LowCaster

    LowCaster Tele-Afflicted

    Age:
    47
    Posts:
    1,071
    Joined:
    Jan 24, 2011
    Location:
    Paris, France
    Thanks. The effects loop in and out jacks were replaced last year, but not the footswitch jack (though the other day I noticed something wrong with it, so you are right there may be something here). Anyway I cleaned everything, jacks and internal connectors, and since then I have been playing 3 hours without any problem...
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.