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I got the "no schematic blues" Dean A-30X acoustic amp.

Discussion in 'Amp Tech Center' started by backpackeraz, Aug 20, 2020.

  1. backpackeraz

    backpackeraz TDPRI Member

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    I was given an old Dean AX-30 solid state amp that was non functioning. Upon opening the chassis, I found a roasted resistor near one of the transistors which was also bad. The bands are difficult to read and the wiring schematics are nowhere to be found, not even from the company. Perhaps somebody with more years of amp doctoring can advise as to the value?

    Here is a link to the transistor info page:

    http://www.datasheetcafe.com/d2059-datasheet-transistor/

    Attached are a few pictures. I removed R70 and R69, you can see where R69 cooked the board, Any help is greatly appreciated.

    -Alex 20200820_125717.jpg 20200820_125738.jpg
     

    Attached Files:

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  2. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Are you sure about that model number? I'm not even finding any existence of an "AX-30" with an online search.
     
  3. backpackeraz

    backpackeraz TDPRI Member

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  4. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Well, the outside is pretty!!! :)

    Seriously, you should be able to go back and edit the first post so folks can look up A30X.
     
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  5. David Barnett

    David Barnett Doctor of Teleocity

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    Are those the emitter resistors for the output transistors?

    Is it just a shadow or does R63 look kind of toasty too?
     
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  6. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Can you get a reading on either resistor with meter?
     
  7. tubeswell

    tubeswell Friend of Leo's

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    If the emitter resistor was toast, so is the transistor
     
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  8. Jon Snell

    Jon Snell Tele-Holic

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    It looks very basic;
    Output transistors are suspect as will the pair of driver transistors, Q5 & Q4 probably. Replacing the burnt resistors, if in the emitters then 0r47 1W is a good choice, and a general careful measuring on the board and it may be OK again.
    One must ask ans find out why it failed in the first place. From the photo there dows not apear to be any thermal stabilisation ... maybe they all failed that way.
     
  9. backpackeraz

    backpackeraz TDPRI Member

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    Would you please explain what thermal stabilsation is? It certainly did come from the emitter.

    I have wondered if there was a design of component flaw that was common in these. I contacted Dean multiple times, the only response: "we discontinued that amp years ago and have no schematics"

    Thank you for your help!
     
  10. backpackeraz

    backpackeraz TDPRI Member

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    I ordered 5 replacement transistors. :)
     
  11. backpackeraz

    backpackeraz TDPRI Member

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    R69- The one that got toasted, is completely open, full continuity and ohms out at .2R

    R70- No signs of scorching, behaves oddly when measuring ohms, initially starting at about 250M ohms and then slowly climbing to about 750M ohms (I double checked my meter with a new 33K resistor to make sure it was working properly.)

    Could they really be that high of resistance?
     
  12. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Must be too far gone to get any good reading of the original value.
     
  13. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I just noticed @Jon Snell said they may be 0r47. Some meters may have trouble reading low resistances.
     
  14. backpackeraz

    backpackeraz TDPRI Member

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    Yes, they are the emitter resistors, R69 does have a little scorching, good catch! Another important thing that I havent mentioned is that some previous "technician" bypassed the fuse and connected the wires directly together. At this point I'm guessing a transistor failed, though I will probably check everything including the PT.
     
  15. ale.istotle

    ale.istotle Tele-Holic Silver Supporter

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    Looks like that amp was made in Korea and private labeled for Dean and some others - Prime and Tanglewood at least. A-30X. No wonder drawings are not to be found.
    [​IMG][​IMG]
    upload_2020-8-21_14-59-37.png
    [​IMG]
     
  16. backpackeraz

    backpackeraz TDPRI Member

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    It could be, though I tried two different meters (a bosch and a wavtek) and get over range indication until I dial up to 20000M
     
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  17. backpackeraz

    backpackeraz TDPRI Member

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    Holy mole, yep, that would do it. I was tempted to trash the board and build a new circuit, but I watched a video on youtube of a fellow playing one and it actually sounded good.
     
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  18. backpackeraz

    backpackeraz TDPRI Member

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    Actually, it was a 15 watt model that looks similar.

     
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  19. Jon Snell

    Jon Snell Tele-Holic

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    That means they are open circuit and the output transistors will require attention.
     
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  20. rangercaster

    rangercaster Poster Extraordinaire

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    Anybody who will try to fix an SS amp has my ultimate respect !!!
     
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