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Speaker Thump Sony TA-88

Discussion in 'Solid State' started by Fhamre, Oct 28, 2007.

  1. Fhamre

    Fhamre AK Subscriber Subscriber

    My vintage mini amp has developed a significant speaker thump on power up.
    The two channels read around 30mv DC. There are no pots to adjust or relay to clean. I have a parts unit, so I tried changing the power switch, no change.
    I don't have a service manual. I could change the power supply caps.
    Any other ideas? This little unit is really well built, but being in such a small package its alot of work to replace parts.

    I seem to be having trouble with the search engine.
     

     

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  2. theophile

    theophile Pheasant Plucker. Subscriber

    Before you do anything to the amp read this recent thread:

    http://audiokarma.org/forums/showthread.php?t=131936

    There's a high chance that taking the '88 to anyone other than someone experienced in working on v-fet amps(like your 88)for repair will be a big mistake.
    Try contacting EchoWars(click on his name in the link above)and send him an e-mail(his e-mail is quicker than his PM box).
    Good Luck.
     
  3. tri-comp

    tri-comp Well-Known Member

    Messages:
    504
    Location:
    Denmark
    Ahem..??
    By all means contact EchoWars for help.
    Just don't ask him to go lookin' for any FET's in this amp, because he'll find none.
    Not according to my Service-manual, anyway.
    The one you can have a free pdf-copy of if you PM me with your e-mail address :D

    Kind regards,

    /tri-comp
     
  4. theophile

    theophile Pheasant Plucker. Subscriber

  5. Stoffie

    Stoffie Sony afficionado

    Messages:
    1,629
    Location:
    Flanders, Belgium
    Yeah, gotta love Sony monikers...easy to get confused.

    The TA-88 is actually a cute little amp...

    [​IMG]
     
  6. theophile

    theophile Pheasant Plucker. Subscriber

    Yup.
    I got it wrong alright. :sigh:
     

     

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  7. Fhamre

    Fhamre AK Subscriber Subscriber

    That's a great picture of the TA-88 Stoffie!
    Thanks for the offer of the service manual pdf tri-comp.
    I sent you a pm.
     
  8. Stoffie

    Stoffie Sony afficionado

    Messages:
    1,629
    Location:
    Flanders, Belgium
    It's a cute little thing, and I love the matching tuner with the big round dial glass.

    [​IMG]
     
  9. Fhamre

    Fhamre AK Subscriber Subscriber

    Another,nice picture. I've got to learn how to take pictures of that quality. Is that your picture?
    I have two sets of the TA-88 and matching tuner. Using one set for parts.
    Remarkable little unit.
     
  10. Stoffie

    Stoffie Sony afficionado

    Messages:
    1,629
    Location:
    Flanders, Belgium
    They sure are cool nifty little things. I do not own them. Found the pictures online at some audio museum site (http://www.hifimuseum.info) :)
     
  11. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    Messages:
    21,085
    Location:
    Bensenville,Illinois
    Fhamre sent me a copy of the manual.

    The power on thump is most likely a capacitor in the power supply that has lost value, and is charging at a different rate than originally intended.

    There are 6 power supply capacitors to change:

    C301 & C302 2200uF 25v on the main amp board, mouser.com part #140-XRL25v2200-rc @ $0.67 ea
    C307 220uF 16v on the preamp board, mouser.com part #140-XRL25v220-rc @ $0.12 ea
    C308 220uF 16v on the main amp board, mouser.com part #140-XRL25v220-rc @ $0.12 ea
    C309 100uF 16v on the main amp board, mouser.com part #140-XRL25v100-rc @ $0.09 ea
    C311 47uF 25v on the main amp board, mouser.com part #140-XRL25v47-rc @ $0.06 ea

    The 4 diode bridge rectifier (d301-d304) could have a bad element that also causes one side to come up slower. mouser.com part # 512-1n5404 @ $0.18 ea

    There could be others, but these are "the usual suspects".
     

     

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  12. Fhamre

    Fhamre AK Subscriber Subscriber

    Great info Mark! I installed the caps I had on hand leaving the power caps and diodes for a Mouser order.No luck so far.
    Never having used Mouser before, I hope they don't have a minimum order of $50.00 and not ship by USPS.
    I'll take this opportunity to order some other goodies I know I'll need.
    Thanks again for the parts list. Will let you know how it ends.:thmbsp:
     
  13. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    Messages:
    21,085
    Location:
    Bensenville,Illinois
    If I can be pointed at some Canadian distributor's website, I'll come up with part numbers that don't have to cross a border.

    Mouser has no minimum (at least for domestic orders, I don't know about "international") and no fee for under a specific amount. They have oodles of shipping options.

    There are other small caps that might have something to do with it, but my bet is on the 2200 uF caps (or those diodes).
     
  14. Fhamre

    Fhamre AK Subscriber Subscriber

    Have done a little homework with Mouser. Seems the cheapest I can get my order shipped is $25.00.
    Still looking for cheaper options as I would like to find a reliable source for parts that will ship via USPS via First Class mail which would be about $8.00.
    I found a small outfit for crossover caps in Oregon, first class personal service, good prices, no minimum,shipped via USPS,same day,shipping cost $3.60.http://www.chokes.com/index.html
    Would be nice to find a similar supplier for a wider range of parts. Courier charge a minimum of $25.00 for a customs handling fee.
    Digikey seems to have a Canadian link. Will try and see what their products,pricing and shipping looks like.
     
  15. Fhamre

    Fhamre AK Subscriber Subscriber

    Finally got the caps and diodes I needed.Installed them last night.
    No success. Even changed a few other caps as well.
    Any other suggestions would be appreciated.
     
  16. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    Messages:
    21,085
    Location:
    Bensenville,Illinois
    Unfortunately, the only thing I can think of is to finish replacing the rest of the electrolytics...
     

     

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  17. Fhamre

    Fhamre AK Subscriber Subscriber

    Ok, I'll carry on with the recap.
    Thx!
     
  18. scotty1000

    scotty1000 New Member

    Messages:
    3
    Hi, I`m looking for a Service Manual for the Sony ST-88. Has someone that in .PDF ? I can swab/offer with Service Manual for Sony TA-88 in .PDF
    Thanks in advance.
     
  19. dspear99ca

    dspear99ca Super Member

    Messages:
    2,247
    Location:
    BC, Canada
    Can you post the schematic?

    If there's a speaker relay how is it powered?

    If there's no speaker relay, there's likely a transistor/rc variant on one of the power rails supplying the outputs.

    Here's how it works. On the power rail there is an RC network with a time constant of a few seconds. Once the cap charges up, voltage at the output rises, which turns on a transistor (or speaker relay), which allows current to flow in the power rail to the output devices (or powers the speaker relay). The few seconds allows everything to stabilize before turning on the amp. The cap in the RC network is shorted, which allows full power to the amp at turn-on causing the thump.

    Dave
     
  20. scotty1000

    scotty1000 New Member

    Messages:
    3
    Hi Dave, you need the schematic of the TA-88? Contact me pls.
    Regards,
     

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