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MusicMan 212-65

Discussion in 'Amp Tech Center' started by James Knox, Dec 4, 2020.

  1. James Knox

    James Knox Tele-Holic Silver Supporter

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    My Grandaughters Boyfriend finds out I’ve been building Amps in my garage WantS to know if I can look at his dead MusicMan. Story is they were jamming and decided to hook up his working Amp to a 410 cabinet, not really knowing about speaker loads and what not. He says the house circuit breaker tripped. When they restored power and hooked the Amp back up to the onboard 212 speakers, no sound. Later he had “a friend” look at it who advised that the Filter Caps were bad, needing replacing.

    This is the Amp

    E7EE97FC-F754-47B8-BA2B-508F9B20277C.jpeg

    056E621B-E989-49E9-9FE3-EB411A15AF25.jpeg

    28B4A18B-BA7A-47E5-A979-AAF7E25DAAEE.png
    On visual inspection I find this in the Dog House...

    57B3B320-305B-4CA5-B4DE-A3C36C4FEFC5.jpeg

    Isn’t it missing 2 Filter Caps?

    765D7BC4-FCD3-4389-B6B7-15CCBD9C0726.jpeg

    I found a pic of a cap job on the web...

    D15C7B2E-6D4C-4720-875D-90E194AF7362.jpeg 86D9D5FA-F8FC-4FCE-8FA1-3ACD8C34FF6D.jpeg

    I hooked the Amp up to my LightBulb Limiter and it lit up bright with no dimming indicating a short. Getting ready to replace the 100uf 450’s. This is my first real Troubleshooting repair. I just started down the New Amp Startup Procedure And got this far.

    Any input of any kind much appreciated!
     
    cyclopean and Nightclub Dwight like this.
  2. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    *Just* had one of these go out the door after being serviced this morning.

    Mine did have those caps and wires like the last picture you provided. Maybe someone has already been in there messing with things, as it seems odd the wires themselves don't exist.

    The good news: dead is usually pretty easy to track down, after a proper cap job.
    The bad news: someone has been in there before and dome *something*

    Likely gonna be some schematic tracing involved here I'd think
     
  3. James Knox

    James Knox Tele-Holic Silver Supporter

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    I installed the 100uf caps. When I turn the power on, the lamp lights. The Standby switch is a 3-way with Standby in the middle, Hi Power in the Up position and Low Power Down. When I toggle to Hi or Low the Lightbulb Limiter lights up full-on and I get a loud hum.


    108363B5-731C-4C16-82CF-C354594A3CAB.jpeg
     
  4. adjason

    adjason Poster Extraordinaire Silver Supporter

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    not much help her but did you check the fuse?
     
  5. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Sounds like more than just a cap issue then
     
  6. James Knox

    James Knox Tele-Holic Silver Supporter

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    yep - fuse good to go!
     
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  7. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Can you determine the hum frequency?
    60Hz
    120Hz
    240Hz

    Can you get voltages?
    B+... (+ side of the caps you installed)
    Tube pins
     
  8. James Knox

    James Knox Tele-Holic Silver Supporter

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    Trying to get an Free App to Determine freq... will advise.

    OK - looks to be 120hz

    D2F7DAD0-98B7-4318-ADEB-F0BFE95E684B.jpeg

    Here are some crazy voltages. Nowhere near the 700vdc listed on the schematic.

    FC181E27-B3FA-432C-BEA1-3B89089CAA1B.jpeg

    Here are the new Filter Caps

    B0DF0F00-E606-4DBC-80CD-1EA6DCA1510B.jpeg

    And the 6CA7s

    4C01B829-E59F-4BCD-8434-76E86747578C.jpeg 7469B880-94F9-4CB0-AF25-81E9BA43DBDD.jpeg
     
    Last edited: Dec 5, 2020
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  9. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Pull the tubes and try the voltages again.
     
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  10. James Knox

    James Knox Tele-Holic Silver Supporter

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    I only had chance to quickly pull he tubes and turn it on. The lightbulb limiter did not glow strong and bright like before! Upon visual inspection, one of the tubes had a bunch of white flakes rolling around inside. I’ll get those new voltages tomorrow morning m
     
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  11. James Knox

    James Knox Tele-Holic Silver Supporter

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    ahah. There those volts are!

    image.jpg

    On pin 3 of both tube sockets I got an “OL” on my meter for High Power. Out of limits?
     
  12. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I did a little reading. The high power is said to be about 700v so with no load it would be over that. Your meter may not go that high.
    Good to see there is voltage. For the most part you can just stick with the low power now that we know it is there.
     
    James Knox likes this.
  13. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I messed with one for a friend this year. The cap board was easy. I didn't touch the PCB. But, he had old EL34's in there that sounded like a cannery when I turned it on. I got a pair of new JJ 6CA7 tubes and that breathed new life into it. F&T caps and JJ's took brought it right back where it needed to be.

    If I remember correctly, they have a neon bulb or something weird that just doesn't work at this point for the most part. The half power switch doesn't really make that much difference. And with his original speakers, I flipped the switch and compared the 2x10 to my Ragin Cajun in a 16x18 pine cab. The Cajun mopped the floor with the original speakers and made them pick up the tab. I could have saved a LOT of trouble shooting if I'd tried a different modern speaker earlier. I kept telling him, "Man, there's no way this amp is putting out near 65 watts." Finally tried a modern speaker...BOOM. I could feel it in my chest.
     
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  14. Dacious

    Dacious Poster Extraordinaire

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    Have you got continuity between primaries and secondary of output transformer?

    I'd say it's cooked. The white flakes in the power tube is a sign the vacuum went. Either the incorrect speaker load/mismatch overheated it or the transformer arced and took it out.

    I'd suspect it was failing and losing volume, causing them to parallel the 410 with the internal speakers and goodnight Irene.

    Those amps are usually frighteningly loud.
     
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  15. James Knox

    James Knox Tele-Holic Silver Supporter

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    @jsnwhite619 Did you replace just the Filter Caps or the caps on the circuit boards as well? Looks like there are 4X 150mf/50, and 5X 20mf/5. Looks like they are soldered from the bottom, so one must Remove the circuit board?

    EE0F8E08-A5DC-4235-BA5E-BB04B683F2F7.jpeg
     
    Last edited: Dec 6, 2020
  16. James Knox

    James Knox Tele-Holic Silver Supporter

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    I don’t have continuity between primary and either secondary on the OT with the Tranny installed. Do I need to unsolder the taps to test?
     
  17. NTC

    NTC Tele-Meister

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    There should be no continuity between the primary and secondaries.
     
  18. James Knox

    James Knox Tele-Holic Silver Supporter

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    I understand that; I was asking if I need to unsolder all the Transformer leads to accurately check or can I leave them wired up and check?
     
  19. NTC

    NTC Tele-Meister

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    Sorry, I misunderstood. You should be able to check with it in circuit.
     
  20. James Knox

    James Knox Tele-Holic Silver Supporter

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    Ok, cool! Thank you.
     
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