SA-7500II recap

Discussion in 'Pioneer Audio' started by loweran, Oct 6, 2017.

  1. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    All,

    I am starting to put a list together for an SA-7500II. This is a working unit and sounds pretty good as is.

    So, the question is, should I just replace the top 10 worst list of transistors in the unit which are only two 798s or should I target more? Also, if the power is good, should I still replace the diodes?
     
  2. Hipocrates

    Hipocrates Anti-Muppet Subscriber

    Messages:
    1,184
    Location:
    Costa Rica
    I have the mk1, if the unit is working fine and the voltages are on spot I would let them alone. I really like this silver amps.
    C0g and PP caps on signal path made a good improvement on mine
     
  3. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    Cool. Thanks. I will post the bom I intend to order here.
     
  4. Hipocrates

    Hipocrates Anti-Muppet Subscriber

    Messages:
    1,184
    Location:
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    Anytime man... if you have some doubts just let me know. You probably know it, but remember to use a DBT on this one to protect the outputs.
    Good luck!:thumbsup:
     
  5. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    Yes sir always do when messing around with one of these.

    I’ll look and see what I have and may go ahead and order replacements just in case. They are cheap enough. I have been ordering more than I need so starting to have a bit of stock.
     
    Hipocrates likes this.
  6. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    Parts should be here tomorrow. May get some time to dig in. I opened it up and it looks like everything is easy to get to. I validated all the e-caps to be as documented in the SM.

    Couple of questions:
    Not sure how to, or if it's required to, re-grease the outputs.
    Looks like the filter caps are multi lead (5?). Anyone know how to convert the 2 lead caps to match?
    SM does not list pin voltages for power and amps. They list transistor voltages.
    I will be replacing the two 2sa798s with pairs of ksc992s I ordered a cheap meter with hFe feature. I assume that will be good enough to match the ones I have. I did try the diode measure on EB and CB on the ones I have and they are all the same.

    Any other notes that I should be aware of?
     
  7. kryten79

    kryten79 AK Subscriber Subscriber

    Messages:
    129
    Location:
    VA Outside D.C.
    I am interested in your parts list. I have an SA-7500ii as well. I have several other Pioneer pieces which need to be checked.

    As much as I've searched this site I am still not certain I have found the definitive recap lists. Marty Socal, markthefixer and mattsd have all contributed.
    The AK database for Pioneer doesn't seem to get updated. The Pioneer Recap STICKY seems iffy. Mattsd has contributed a bazillion brain droppings across the site. Maybe it's time for a Moderator to become involved? Would it be possible to create a sticky or use the document database for definitive lists to which only a few members could contribute? Start by pulling the most current versions of recap lists into one place and freezing the old, lengthy threads? I'll forward this post to a moderator. Not certain if I'm overstepping boundaries here. If so, my apologies.
     
  8. Cuppy

    Cuppy AK Subscriber Subscriber

    Messages:
    163
    Location:
    Maine
    loweran,

    I recently completed a restore on my 7500 II. I did not bother to re-grease the outputs on mine so can't comment on procedure. The original filter caps are multi lead but only 2 leads are actually connected to solder traces, the others are just used for stability. I also did not replace the 798's since the measured offset was well within tolerance and equal on both channels. If you do decide to replace with the 992's you will notice the board will have the extra hole so you will not need to double up the emitters.

    When I first received my 7500 it was going in and out of protection. The problem was narrowed down to the protection relay driver transistors being faulty. Sorry I didn't make up a BOM for this unit when I did mine.
     
  9. Cuppy

    Cuppy AK Subscriber Subscriber

    Messages:
    163
    Location:
    Maine
    One thing I forgot to mention...Pay careful attention to the orientation of caps C23 and C24 (2.2uf 50V). The originals on my amp were installed with reverse polarity than the schematic and screen print. Since I couldn't get a definitive answer on which was correct, I elected to install bipolar caps in those locations.
     
  10. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
  11. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    Good call. I will pay close attention. I did go through and spot check most of the caps to the documentation to see if they matched. Cant always see the screen print under the cap. Mine is a working unit and untouched. I will put them in the way they came out.
     
  12. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    Just verified that C23 and C24 are installed opposite the SM and the silk screen.
     
  13. Cuppy

    Cuppy AK Subscriber Subscriber

    Messages:
    163
    Location:
    Maine
    Just as I suspected. Since I never received a definitive answer as to whether it was an error with the SM and silk screen or an error with the factory install, I decided to replace with a bipolar so it wouldn't matter. May not make any difference since it worked before the recap from the factory. Wish I knew/understoold more about the design if the circuit.
     
  14. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    Here is what I have found so far:

    C23 and C24 installed opposite of the SM and silk screen
    R91 - 680 2W looks burned
    R51 150 .5W looks burned
    R97 270 .5W looks burned
    R52 150 .5W looks burned

    Lots of cold solder joints

    Repair work done prior
    Q15 replaced
    Q11 replaced
    D9 replaced
    R97 replaced
    Q5 replaced
     
  15. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    Done with the caps except for the filters. Did not do the transistors yet since I don't have my meter. Left channel reading 30mv. Right channel reading 15.5mv
     
  16. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    Damn, the filters I have don't fit and too big to stuff the can. Wonder if I can mount them off the board and use wire. Thoughts?
     
  17. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    Here is a pic because I like pics.
     

    Attached Files:

  18. Cuppy

    Cuppy AK Subscriber Subscriber

    Messages:
    163
    Location:
    Maine
    loweran,

    I just posted this pic in your other thread regarding the filter caps.

    recap.jpg
     
  19. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    Got them wired in. Got some 14awg solid 300V wire and wired them up. Worked great.
     

    Attached Files:

  20. loweran

    loweran AK Subscriber Subscriber

    Messages:
    878
    Location:
    Austin, Texas
    Sounds pretty bad. I have 60VDC on the right channel speakers and 23VDC on the left. Voltages at the transistors seem off. Going to have to investigate. I noticed a couple of resistors looked burned as listed above. May start there. Probably going to need to replace some transistors too.
     
    Last edited: Oct 25, 2017

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