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Thread: 5150 hideous death

  1. #1
    Old Timer tedmich's Avatar
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    5150 hideous death

    I picked up a dead 5150 "signature" model Peavey for very cheap and was hoping the Q7 switching JFET had gone out like the 6505+ I just got...opened it up and was met by this:

    photo-1-u002525282-2529.jpg
    photo-u0025252897-2529.jpg
    again I am a victim cause I have no sense of smell!

    two SGRs were open and several other resistors cooked, but it was the "protection diodes" which nuked the PA board
    photo-u0025252896-2529.jpg
    Since I have the 6505+ open I can sub in its PA board to see if 5150 is worth fixing. Looking at the older PA board I figured I could make a newer version one faster (and cheaper) than ordering one from PV, so I etched one.
    photo-u0025252898-2529.jpg
    The old sockets don't fit without some lead bending, and it won't ever look stock but WTF. I moved some traces and tied the pin 1&8 on the last tube so EL34s could work if I mod the bias. I think I'll go with 2 parallel 1.5k 3w SGRs.

    Now to fire up the old tube tester to see which (if any) of the 12 Ruby 6L6s are good...
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  2. #2
    Senior Member Enzo's Avatar
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    Those diodes probably saved your OT. That is their job.
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  3. #3
    Old Timer soundguruman's Avatar
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    Burning of the output board is pretty common on Peavey amps.
    And the board is riveted to the chassis...
    They usually won't sell new boards to repair it.

    Any black carbon on the board will continue to burn, until it is completely removed. So, the board is often JUNK.

    However, mounting regular sockets on the chassis,
    you can point to point wire it.
    It's been done many times successfully.

  4. #4
    Senior Member Enzo's Avatar
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    Once again...

    The board is not riveted, the sockets are.


    And in my experience over the decades is that such a board burn is NOT common.

    And furthermore, they WILL sell you a new board if they have one.
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  5. #5
    Old Timer soundguruman's Avatar
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    Quote Originally Posted by Enzo View Post
    Once again...

    The board is not riveted, the sockets are.


    And in my experience over the decades is that such a board burn is NOT common.

    And furthermore, they WILL sell you a new board if they have one.
    Usually burns cause wrong impedance speaker, or bad speaker cable.
    Starts arcing, and continues...
    601 483 5365
    Let's see how easily you can buy one....hahahahahahahahah! (good luck)
    (all previous attempts to buy output boards have failed, that's what's funny)

  6. #6
    Old Timer tedmich's Avatar
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    i like etching boards so I decided to do that, I did move some traces so I could put in 6 small holes for a hex key to tighten some socket head screws to test fit it without rivets, gotta be sure the main board is AOK as R69 (4.7k) blew up pretty bad.

    You are right Enzo PV would sell me a new PA board but I am cheeeep. Main board is also available from PV... for about $350!

    Its refreshing to have two sides to tech issues now; Enzo on the right and SGM on the left!
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  7. #7
    Supporting Member Jazz P Bass's Avatar
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    That does not look like 'ordinary' damage.

    Ten to one there where multiple attempts at fuse/ tube replacement & then the fire started.
    Last edited by Jazz P Bass; 01-29-2014 at 12:11 AM.
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  8. #8
    Old Timer tedmich's Avatar
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    yah guy seemed deceitful but he had a really cute 4 yr old and the price was LOW, and I like to think I can fix anything (or at least anything as simple as 1st gen 5150!)
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  9. #9
    Supporting Member The Dude's Avatar
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    Yep, as Jazz hinted. Be sure to check all fuses and make sure they are the correct value. Chances are good you'll find a 20A fuse in there.
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  10. #10
    Supporting Member Jazz P Bass's Avatar
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    In the case of those high voltage diodes, they can fail short.
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  11. #11
    Senior Member Enzo's Avatar
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    That is what failed and burnt - the OT protection diodes.
    Education is what you're left with after you have forgotten what you have learned.

  12. #12
    Old Timer tedmich's Avatar
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    I think I'll replace them with RGP02-20E, 2kv 300ns at 0.5A for $0.20 each

  13. #13
    Old Timer soundguruman's Avatar
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    Quote Originally Posted by Jazz P Bass View Post
    That does not look like 'ordinary' damage.

    Ten to one there where multiple attempts at fuse/ tube replacement & then the fire started.
    I can't even COUNT how many output boards I have seen burn in PV amps...just like this one.
    So, if you fix a lot of PVs, it's "ordinary." (as I have since mid 1970s)

    This is why many times, they just mount sockets, and wire it PtoP.
    Fiberglass may not be an "ideal" material...

    But don't be discouraged, plenty of them have been salvaged plenty of times.

    However what you don't want to do, is reuse a burned board, cause it will just keep burning.
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  14. #14
    g1
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    don't forget the joker g1's Avatar
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    If you can't count that high or don't have extra fingers, how about just a rough guess and tell us.
    You make it sound like it is a large percentage of all the Peavey amps you have serviced.
    Certified Dotard

  15. #15
    Senior Member Enzo's Avatar
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    See, the problem is that the fingers on one hand look a lot like the fingers on the other hand, so the count gets confused.

    Anyone who works on amps for a living knows this is a lot of hot air.



    Then again, even with my shoes off, I can;t count past 21.
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  16. #16
    Supporting Member The Dude's Avatar
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    There are certainly posts here that you must take with a jar of salt. A grain simply won't do it.
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    Supporting Member eschertron's Avatar
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    Quote Originally Posted by Enzo View Post
    See, the problem is that the fingers on one hand look a lot like the fingers on the other hand, so the count gets confused.

    Anyone who works on amps for a living knows this is a lot of hot air.



    Then again, even with my shoes off, I can;t count past 21.
    Did you say... :koff: :koff: .. just your shoes off?
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    Quote Originally Posted by Steve Conner View Post
    If it still won't get loud enough, it's probably broken.

  18. #18
    Supporting Member The Dude's Avatar
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    Quote Originally Posted by soundguruman View Post
    I can't even COUNT...
    Maybe should have just quit right there.

  19. #19
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    It would be very surprising to have things burn so bad if the amp is stock. Someone must put a much bigger fuse. I don't believe speaker impedance mismatch will do it unless you use a 32 ohm speaker on an OT for 2 ohm and whale it full tilt.

  20. #20
    Supporting Member Chuck H's Avatar
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    You guys stop picking on SGM! (that's my domain )

    Seriously though. It's entirely possible that he's seen a disproportionate number of burned boards in Peavey's and is actually trying to be helpful. And his misinformation about construction and parts availability may be due to his experiences with similar Peavey products and he mistakenly assumed the same problems would cross over to this model. I say this because of my personal experience with those damn black fiber boards in vintage amps. I'm convinced that they are all conductive or will be to a greater or lesser degree. But that's because of my own disproportionate experience with them. The vast majority of techs have seen many more than I have with no incidence. But I'll warn against them every chance I get.
    "The man is an incompetent waste of human flesh. He should donate his organs now to someone who might actually make good use of them." The Dude re: maybe I shouldn't say, but his name rhymes with Trump

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  21. #21
    Senior Member Enzo's Avatar
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    Conductive black eyelet boards is a problem everyone should be AWARE of. I have found them time to time for years, but MOST eyelet boards are not conductive. I will tell someone to check it, because it is a quick simple test, but I wouldn't rant how all Fender amps have conductive eyelet boards.

    SGM has a history here of extrapolating from a sample of one to entire product lines. This is another example of it. Claiming that this happens to a lot of them doesn't further the particular repair, it doesn't suggest something to check, it suggests no diagnostic.


    I'll stop picking on him when he stops making shit up.
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  22. #22
    Old Timer tedmich's Avatar
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    every 5150 I've ever owned has had a burnt board EXACTLY like this!

    Scientific rigor does not come naturally, and without it I am much more prone to hyperbole and emotional leaps of faith. But it really works best when making and fixing stuff, IME.

    I'm currently fighting the nonscientific urge to replace every horrid carbon resistor in this unit with beautiful bulk foil ones (or tantalum!) as I write this.....Urgh! Ack!
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  23. #23
    Supporting Member Jazz P Bass's Avatar
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    I had a 100W Carving come in like looking something like that.
    They had the board in stock.
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  24. #24
    Old Timer soundguruman's Avatar
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    Quote Originally Posted by tedmich View Post
    every 5150 I've ever owned has had a burnt board EXACTLY like this!

    Scientific rigor does not come naturally, and without it I am much more prone to hyperbole and emotional leaps of faith. But it really works best when making and fixing stuff, IME.

    I'm currently fighting the nonscientific urge to replace every horrid carbon resistor in this unit with beautiful bulk foil ones (or tantalum!) as I write this.....Urgh! Ack!
    1. Non- scientific?
    2. When the fiberglass turns black, it's becoming carbon.
    3. Carbon conducts electricity. Same as a carbon resistor.
    4. Follow me so far?

    5. The carbon continues to conduct electricity, and the board becomes black-er.
    6. It will work for a while, until the carbon shorts it out.

    7. The last 2 5150s I worked on were NOT burned. Not every one of these turn black.

    8. But sooner or later, the damaged board will become charcoal.

    9. The method of using sockets, wiring P to P, is superior. It's the only real dependable permanent repair.

    10. Whether or not you accept it, the reality remains. Carbon conducts electricity.

    You can use a mega- OHM meter, to verify the leakage between the circuit tracks. It's UN-deniable.
    If you choose to ignore what your ohm meter is telling you, than have fun, in your alternate reality.

  25. #25
    Supporting Member Chuck H's Avatar
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    I didn't see where any one was advocating using the charred board. What you're saying is something well known to any half baked tech that's worked on an amp with a arched tube socket, cooked resistor, blackened insulator, etc. I even know of one instance where a fire started because the carbon particles on a fluorescent lamp socket caked up too much and melted the plastic mount, dropping flaming plastic onto the couch beneath it.
    "The man is an incompetent waste of human flesh. He should donate his organs now to someone who might actually make good use of them." The Dude re: maybe I shouldn't say, but his name rhymes with Trump

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    Senior Member Enzo's Avatar
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    Oh forget him. This is classic SGM bait and switch. He starts by claiming that the 5150s do this ALL the time. Then comes back explaining that charred boards are conductive. But of course that was not the original assertion. Just a form of floor-holding.
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  27. #27
    Old Timer tedmich's Avatar
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    Quote Originally Posted by soundguruman View Post
    1. Non- scientific?
    2. When the fiberglass turns black, it's becoming carbon.
    3. Carbon conducts electricity. Same as a carbon resistor.
    4. Follow me so far?

    5. The carbon continues to conduct electricity, and the board becomes black-er.
    6. It will work for a while, until the carbon shorts it out.

    7. The last 2 5150s I worked on were NOT burned. Not every one of these turn black.

    8. But sooner or later, the damaged board will become charcoal.

    9. The method of using sockets, wiring P to P, is superior. It's the only real dependable permanent repair.

    10. Whether or not you accept it, the reality remains. Carbon conducts electricity.

    You can use a mega- OHM meter, to verify the leakage between the circuit tracks. It's UN-deniable.
    If you choose to ignore what your ohm meter is telling you, than have fun, in your alternate reality.
    As a chemist I understand that carbon conducts, yes. Thats why I etched a new board. My preference is to avoid mixing PTP with PCB. I originally posted because the burning was extreme; I could find no other posts or pictures with a comparably burned 5150 board. You stated that these were common in your experience. Others did not agree. Thanks for the input!

  28. #28
    Supporting Member Jazz P Bass's Avatar
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    And SGM enjoys proselytizing.

  29. #29
    Supporting Member Chuck H's Avatar
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    Quote Originally Posted by Enzo View Post
    Just a form of floor-holding.
    Screw that! I am the all knowing, all seeing "Chuck H"!!!...

    "Oh wait, Enzo's here?... Never mind"
    "The man is an incompetent waste of human flesh. He should donate his organs now to someone who might actually make good use of them." The Dude re: maybe I shouldn't say, but his name rhymes with Trump

    "...less ear-friendly but handy for jazz." Leo_Gnardo

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    As one that designed pcb for years and used exclusively pcb in my career, I do not think FR4 pcb is inferior to wired boards. PCB do not burn easier than wired boards. It's all about the person that layout the board. I layout high current boards into amps of current, I layout boards for 10KV+. It is all about the layout technique. Don't blame on the pcb for incompetent designers.

    Many ignorant pcb designer use too thin a trace, putting high voltage traces too close together. When you have high current trace going from one layer to the other, you need double or triple vias. Some people use heavy trace but only one via to go to different layer, you burn at the via!!!! This is no different from using too small wire for high current signal!!!

    As for conductive fiber boards, I have no experience. But I have a lot of experience of conduction of materials with high voltage. In high voltage design, there are two distinct issue of conduction. One is insulation and the other is creepage.

    1) Insulating resistance is very easy, most non conductive dielectric is in the ball park of 400V per mil. A piece of paper can insulate hundreds of volts easily. In real life, this is really not an issue as long as you design for say 100V per mil.

    2) Creepage, which is current travel along the surface of an insulator due to humidity and contamination. This IS the big issue with leakage and arc through. The number depends on the material, humidity, flux and all sort of contaminants. I have to get the book to know the general number. This is spec in CE test manual. I personally do not believe the fiber material have conductive issue, more because of the flux on the surface, the moisture it attracted on the surface that cause the problem. I can tell, Fender do not clean out the flux on the fiber boards, if people start monkeying with mods, they add more flux on the surface every time they solder stuff on. I think that's what's happening. Scrape the flux off the surface when the flux solidified and see whether you can fix the leakage.

    I don't know the circuit of the burn board, it's hard to comment. Does that part have high voltage or current? If it is high voltage, then look for creepage path. I route channel between two pads with high voltage differential to eliminate creepage. If it is current, look for bottle neck along the signal trace. Don't generalize and make assumption.
    Last edited by Alan0354; 01-31-2014 at 06:20 AM.
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  31. #31
    Old Timer tedmich's Avatar
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    working on my 5150 again, found this modded board pic online

    peavey-5150-head-220839.jpg

    LOL!!
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  32. #32
    Senior Member Enzo's Avatar
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    Ewg...
    Education is what you're left with after you have forgotten what you have learned.

  33. #33
    Supporting Member Chuck H's Avatar
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    I can understand not wanting to remove the board, but that's crap. OTOH, wouldn't the board have needed to come out to remove the old caps? You might be able to solder the wired from on top, but not well. Maybe whoever did that just RIPPED the old caps out to access the holes or maybe the component leads were still there?

    I'll admit that on Mesa boards with the rebranded ATOM caps (axial) I have snipped out the old caps, leaving the leads sticking out of the board and then loop/bend soldered them to replacement caps. Seemed like a perfectly acceptable connection and way easier than removing the board. But I would never even think to try something like that with radial caps.
    "The man is an incompetent waste of human flesh. He should donate his organs now to someone who might actually make good use of them." The Dude re: maybe I shouldn't say, but his name rhymes with Trump

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  34. #34
    Supporting Member The Dude's Avatar
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    Hard to tell for sure from the picture, but I suspect that the repair was done as it was because the replacement caps were too tall to solder in as the original caps were and fit into the cabinet. It's still not acceptable. That's what rulers and calipers are for. It might have been a good idea to measure the original caps and replace them with something that would fit into the amp.
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  35. #35
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    Quote Originally Posted by Alan0354 View Post

    2) Creepage, which is current travel along the surface of an insulator due to humidity and contamination. This IS the big issue with leakage and arc through. The number depends on the material, humidity, flux and all sort of contaminants. I have to get the book to know the general number. This is spec in CE test manual. I personally do not believe the fiber material have conductive issue, more because of the flux on the surface, the moisture it attracted on the surface that cause the problem. I can tell, Fender do not clean out the flux on the fiber boards, if people start monkeying with mods, they add more flux on the surface every time they solder stuff on. I think that's what's happening. Scrape the flux off the surface when the flux solidified and see whether you can fix the leakage.
    .[/B]
    I do airborne electronics PCB's for a Laser Airborne Depth Sounder survey system - 2 examples: Q-Switch Driver boards for the laser at 4.5kV and Photomultiplier Power Supply (for the Laser Receiver) at 2.5kV.

    FR4 boards are fine - get the layout right, clean bare boards thouroughly before loading, again after loading and then finally spray with Conformal Coating. The last step (conformal coating) is paramount for reliability. I would suggest that this should be standard practice for tube amp boards.

    Cheers,
    Ian
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