1994 Fender Blues Deville 2x12 -- Awful Noises

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by SmugCat, Mar 10, 2018.

  1. SmugCat

    SmugCat Member

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    Hi y'all! First post here--be easy on me. Following the tech question format stated at top of the forum. If any more information is needed, please let me know.
    (1) AMP: 1994 Fender Blues Deville 2x12

    (2) PROBLEM: Something utterly dreadful is happening with my amp. I've had it for about eight years now and this is the first time I've seen an issue. Randomly while playing, the amp makes God awful noises that are hard to describe. Screeches and loud pops and more -- it's a freakin' circus. I took it to my amp guy to get it fixed up. He tested every connection, checked every solder. Everything looks solid. We tried swapping out power tubes; no dice. Swapped pre-amp tubes; even less dice. He and I are both at a loss.

    (3)SCHEMATIC: http://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-Blues-Deville-Schematic.pdf

    Only a single mod on this amp--linear to audio taper. Everything else seems in tip-top shape. If it'd help, I could provide an audio recording of the noise? No idea what to do here. Someone help?
     
    Last edited: Mar 11, 2018
  2. jnovac1

    jnovac1 Supporting Member

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    bad input jack?
     
  3. Jeff Gehring

    Jeff Gehring Silver Supporting Member

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    Since your amp is a '94, you might have your tech check to see if Fender Tech Note 94-7 has been done on the amp.

    It calls out the replacement of two power resistors in the low voltage supplies that get so hot they desolder themselves.

    [​IMG]
     
  4. SmugCat

    SmugCat Member

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    Had them replaced as well. Forgot to mention.
     
  5. SmugCat

    SmugCat Member

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    Thx for that insight, Jeff. I know my tech checked all solder points, but perhaps he overlooked these? I can have him check this week.

    If it was overheating and desoldering itself, wouldn’t it be all noise from then on rather than intermittent noise?
     
  6. Jeff Gehring

    Jeff Gehring Silver Supporting Member

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    Not always. Sometimes they are only intermittently symptomatic. Also if they haven’t been replaced, they should be.
     
  7. SmugCat

    SmugCat Member

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    Good thinking. Thanks, Jeff. Hopefully it’ll help.
     
  8. Wag

    Wag Member

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    Check the pilot lamp socket for shorts and the wires for signs of overheating.

    The socket in a friends de ville had been intermittently shorting out for an extended period of time (previous owner). Would cause a lot of audio racket when it did. The PCB and wire both showed signs of exteme heat.

    Unfortunately though ..... in the course of replacing the socket, the jostling of the pcb around to get access to the back side has knocked something else loose. No (appearant) audio signal. Amp lights up but makes no sound. Well, unless you move the speakers to the EXT jack. THEN you can hear a faint signal. Weird. Gonna trey an audio probe on it later, see what I can find there....
     
  9. Johnny Cache

    Johnny Cache Member

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    Yeah, those 2 power resistors seem to be a common problem on HRD amps, need to be replaced and set further apart, from what I understand.
     
  10. Tone_Terrific

    Tone_Terrific Supporting Member

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    How frequently do the noises occur?
    Can they be induced by any particular signal or channel path, or by wiggling a specific part or area?
    Plug into the pwr amp in jack to disable the preamp signal, still there?
    Jumper said loop to test jack connections.
    Fender boards can have poor solder connections.
    Your tech should have done all this, however.
    If the noises are consistently repeating it should be traceable. If they are truly random and infrequent....I hate that:waiting
     
    SmugCat likes this.
  11. SmugCat

    SmugCat Member

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    Any idea on the temperature they get up to that causes the problems? I removed the back panel and watched it with a thermal imaging camera to see if any areas looked problematic, but the temperature range all looked pretty even.
     

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