Peavey PA-200 Head Repair

Discussion in 'Amps and Cabs [BG]' started by jetfuelsuitcase, Apr 18, 2024.

  1. jetfuelsuitcase


    Apr 6, 2024
    Hey y’all!

    FE1B7563-2CFF-40B6-89D3-40BF8E97A60D.jpeg IMG_3595.jpeg First post so I apologize if it’s not in the right area. I’ve got my first “big boy” bass rig now, after having a little practice amp. It’s a mid-70’s Peavey PA head and a cool early Peavy 215 cab. Looks great, but the head is having some issues.

    When I got it, I hooked it up to the cab (with a proper speaker cable), switched it on and immediately it put out this REALLY loud buzz/hum through the speakers. It sounded like 60hz, but it happened a while ago so I can’t be sure. It did that regardless of whether an instrument cable was plugged in, and none of the controls changed the volume of the buzz. After about 20 seconds there was a hissing noise with a pop, white smoke poured out and then I pulled the plug. It ended up being what I think is the coupling cap, the single large 1000/50 on the output.

    I ended up recapping the whole power amp section, and I replaced the white cement resistors as well because they looked a little dodgy. I also noticed that the temperature sensor was never soldered in at the factory, so I soldered those connections as well. No blown fuses or anything. I believe this is the same as the Peavey Century 100 power amp section. IMG_3595.jpeg

    I put it back together, all excited to play through it, plugged it in and the same thing happened!! Loud buzz, before I could pull the plug it blew the brand new coupling cap. I’m no electronics guy, I’ve got no idea what I’m doing. I could try replacing the output transistors next, but I really don’t want to just keep throwing parts at it. Can anyone help me out? Thanks!!

    Attached Files:

  2. Geri O

    Geri O Endorsing Artist, Mike Lull Guitars and Basses Gold Supporting Member

    Sep 6, 2013
    Florence, MS
    At this point, the only logical solution is to ship it to Peavey where they can troubleshoot the issues correctly and make the appropriate repairs.

    You’ve already spent money on a bad (or no) diagnosis. You don’t need to do it again.
  3. eniac


    Aug 26, 2023
    Any competent tech should be able to figure things out. Where you made your mistake was assuming the damaged components were the cause of the problem instead of looking for the real problem -- the one that damaged those components.
    creaturegods and Bill Whitehurst like this.
  4. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Having no idea what you were doing, randomly replacing parts, and now you new problems in addition to whatever original problem your amp had… Classic mistakes that I see all the time.

    Good luck finding a qualified service tech to work on it now. IME, most will say sorry they don’t work on failed repair attempts.
    MCF, john m, herndonbassist and 7 others like this.
  5. jetfuelsuitcase


    Apr 6, 2024
    Well, it’s a good thing I’m not looking for a qualified tech to send it to ;)

    I paid $50 for this amp, and finding a local tech or sending it to Peavey for repair would cost me far more than it’s worth. My intent with this post was to try and get help with diagnosing the issue at hand, so I can troubleshoot it myself, and potentially, help someone in the future when they encounter a similar failure and try to google it. Referring me to a tech does neither of those things. Perhaps it’s my fault, I should have posted this on an electronics repair forum instead. And besides, I won’t have an idea of what I’m doing until I’ve done it :)
    MARVIN MECKLER likes this.
  6. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Another suggestion? How about learning about electronics first, that way you have a better idea of how things are supposed to work and why accurate troubleshooting is part of a successful repair.
    MCF, creaturegods, Aqualung60 and 6 others like this.
  7. salcott

    salcott Supporting Member

    Aug 22, 2007
    NYC, Inwood.
    Nah. Like we used to say in the Army, that would be sensible.
    MCF, TheReceder, shoot-r and 4 others like this.
  8. groovaholic

    groovaholic Protect your hearing. Supporting Member

    Sep 19, 2004
    Mount Prospect, IL
    You're correct that it's the same power amp section as the Peavey Century 120/200; a primitive, but cool- sounding circuit. I've owned several, and I'm a fan.

    But from your description, the power section in yours is FUBAR.
    You could probably replace the whole amp for less than you could get it repaired - a Century from that same generation just sold on my local Facebook Marketplace for $80.

    Your current (blown) amp looks clean, so it would be a good parts donor if the amp you find is beat up but still kicking (the way SO MANY old Peaveys are).

    A couple years ago, I bought a PA200 head to scavenge its power section into one of my a blown Centurys.
    The aluminum knobs are coveted by Peavey nerds, so I took all the knobs off, and sold them on Reverb for $40.
    My point being, if you paid $50 for the whole amp you can probably recoup 80% of your purchase price if you play your cards right...
  9. JFlo

    JFlo Supporting Member

    Jun 23, 2019
    Hi and welcome to TalkBass! I know we live in the era of 5 minute YouTube hacks, but learning electronics takes a lot of study. I'm an amateur and know my limitations so please don't take this as snark. Do you have a DMM, scope, variac, current limiter and capacitance tester? It is important to learn how to read a schematic and understand what each section of the amp is supposed to do, then take measurements of what it is actually doing. There are tons of electronics tutorials on transistors, unregulated power supplies, voltage amplifiers etc that will help in addition to guitar amp specific resources like or the valve wizard. This is a great amp to learn on. Set your goals and decide if you are willing to put in the time required for education.

    MARVIN MECKLER Suspended

    Apr 14, 2024
    I'm not saying you're not getting good advice from the old clan here, but don't be discouraged!

    That's how you learn!

    Of course, you have to have SOME clue how electronics work.

    Then again, there seems to be a huuuuuge amount of people (and others) here who will discourage even the most experienced to try to fix something.

    I find it quite humorous however that those who yell the loudest, "STOP!!! YOU DON'T KNOW WHAT YOU'RE DOING!!!" are the same ones who say these old Class AB amps are sooooo worthless that they can't be given away. But don't you DARE try to fix it!

    It's an old Peavey head - a GREAT one at that - but I'm sure there are a lot of old dinosaurs and horses and snakes and tigers here who have blown up their fair share of amps learning along the way.

    Read up, get the basics down, and fix that thing!
    Last edited: Apr 18, 2024
  11. No doubt. Have to start somewhere.

    MARVIN MECKLER and WayneP like this.
  12. grubdumpling


    Oct 17, 2023
    Winnipeg, MB
    Nice bass, OP

    MARVIN MECKLER Suspended

    Apr 14, 2024
    Nice cab too, OP
    WayneP likes this.
  14. Gervais Cote

    Gervais Cote Supporting Member

    Oct 30, 2023
    Usually, among things that can blow a capacitor, here are the main ones :

    Inverted polarity
    A shorted resistor
    A connection done the wrong way

    And the components that often fail are the electrolytic capacitors, tantalum capacitors, resistors and transistors. Transistors are designed to last forever but when a component near by starts to be defective, they can be damaged.

    When well maintained, only the electrolytic and tantalum caps should be replaced, sometimes a few resistors.

    Some amps also need a bias adjustment when replacing parts.

    I would also look at any trace of heat on components and both sides of the boards, that can give a clue about a defect part.

    Hope this helps !
    MARVIN MECKLER likes this.
  15. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Actually, that's not how most successful folks learn.

    The discouragement is not for the learning part of this, but for the guessing WITHOUT the learning part, or the understanding of how dangerous some faults can be under some circumstances. The lack of safety knowledge is an important reason not to play around with something that you don't have at least a solid basic understanding.

    The OP had a repairable amp, he "messed with it" and now he has an amp that may no longer be repairable because we don't know what kind of additional damage may have been done. The amp may not be worth repairing economically, but just like a broken hammer may not be good for pounding nails it can still cause a lot of damage in the wrong hands.

    Rather than blowing up amps (I didn't blow up amps at the beginning of my career, any more than I blow amps up today, which is none), it's far better (and safer) to learn how they work first. If somebody isn't willing to put the effort into this step, then this is not a great project for them.

    The fault of a failed electrolytic cap can result in an explosion (rapid depressurization of the containment vessel) that can launch electrolyte and bits of aluminum into eyes. That's why we eye protection when powering up an amp with a replaced or suspected bad electrolytic cap. It happens and it's dangerous.
    Murch, MCF, creaturegods and 7 others like this.
  16. J Wilson

    J Wilson Supporting Member

    We get these types of questions about guys trying to repair amps who are just barely capable or not at all.

    Then they lose patience with the professional advice they receive, in its most basic form being: You could very easily be poking around in something that could seriously injure or even kill you, due to your lack of knowledge.

    I don't understand.
    MCF, Aqualung60, Geri O and 2 others like this.
  17. Axtman

    Axtman Supporting Member

    Mar 3, 2008
    Seattle, WA
    The first project you should make is a dim bulb limiter. I use mine all the time. I never plug an amp directly into the wall without the amp passing the dim bulb limiter. This will probably prevent future failures.

    Google "dim bulb limiter" to see different ways to construct this device. The hardest part will be finding incandescent light bulbs. ;-)
    MARVIN MECKLER likes this.
  18. Adienn7


    Jan 26, 2007
    you got to walk before you run.. and make sure you don't get shocked.. I believe that's a new enough of an amp to have a grounded plug.. but you have a lot to learn to fix that amp..
    Aqualung60 and agedhorse like this.
  19. Adienn7


    Jan 26, 2007
    Here's what AI had to say.. great learning tool.. but it's a tool not a replacement for real

    It sounds like you’re dealing with some issues related to your Peavey PA-200 head. Let’s troubleshoot this together! Here are some steps you can take to diagnose and potentially fix the problem:

    1. Check the Coupling Capacitor: Since you’ve already replaced the coupling cap, it’s essential to ensure that the new one is correctly installed. Make sure the polarity is correct, and there are no soldering issues.

    2. Inspect the Output Transistors: You mentioned considering replacing the output transistors. This is a good step to take. Faulty transistors can cause issues like the loud buzz and smoke you experienced. Check for any signs of damage or overheating.

    3. Verify the Power Supply: Ensure that the power supply voltage is within the specified range for the PA-200. Incorrect voltage can lead to problems. Also, check the power supply components (diodes, capacitors, etc.) for any issues.

    4. Inspect the Circuit Board: Look for any burnt traces, cold solder joints, or loose connections on the circuit board. Resolder any questionable joints and ensure proper connections.

    5. Test Without Speakers Connected: Disconnect the speakers and turn on the amp. If the buzz/hum persists, it’s likely an issue within the amp itself. If not, the problem may be related to the speaker cabinet or wiring.

    6. Check the Input Section: Verify that the input jacks and associated components (such as input resistors) are functioning correctly. Faulty input components can cause noise issues.

    7. Test with a Dummy Load: If you have access to a dummy load (a resistor load that simulates a speaker), connect it to the amp’s output. This will allow you to test the amp without risking damage to your speakers.

    8. Inspect the Temperature Sensor: Since you noticed the temperature sensor was never soldered in at the factory, ensure that it’s correctly connected now. A malfunctioning temperature sensor could affect the amp’s behavior.

    9. Fuse Check: Although you mentioned no blown fuses, double-check the fuses anyway. Sometimes a fuse can appear intact but still be faulty. Use a multimeter to verify continuity.

    10. Seek Professional Help: If you’ve exhausted all troubleshooting steps and still encounter issues, consider taking the amp to a professional technician. They can perform more in-depth diagnostics and repairs.
    Remember that working with electronics can be hazardous, especially when dealing with high-voltage components. If you’re not comfortable or experienced with amp repair, it’s best to consult a professional. Good luck, and I hope you get your Peavey PA-200 back in working order! 123

    !Peavey PA-200

    Disclaimer: The information provided here is for guidance purposes only. Always exercise caution when working with electronic equipment.
  20. Adienn7


    Jan 26, 2007