Should I change out these SX-1280 output Transistors ?

Discussion in 'Pioneer Audio' started by Poasttoastie, Feb 7, 2019.

  1. Poasttoastie

    Poasttoastie Member

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    Should I change out these output transistors out on this 1280 that I am trying to freshen up? They test good but as you can see in the pictures they have small burn spots with what looks like copper showing. What could have caused this and where should I check for other issues that may have? Is there a source other than Ebay to find replacements for them and for the clear insulating pads? Or, can the insulating pads be fabricated somehow?
    Thanks! 1280 Outputs 1.jpg 1280 outputs.jpg
     

     

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  2. Poasttoastie

    Poasttoastie Member

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    [​IMG]
    markthefixerOn Hiatus, dealing with Dad's estate full time Subscriber
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    Keep the originals if they are all working together correctly.
    There is a LOT of work involved in changing over to more modern transistors - INCLUDING fabricating some PC boards for in the heat sinks.

    That metal should be electrically isolated from the heat sink, so check the insulators for damage. Large currents are involved, since the collectors are connected to the hot sides of the big capacitors.
    LOTS of reserve energy before fuses blow.
     
  3. Watthour

    Watthour Electron Rancher - JS3600

    Hopefully that was due to contamination, and not any failed mica washers. In either case, new insulation and NON-CONDUCTIVE thermal paste is a really good idea - IF you can find suitable mica washers. Sil-pads would be a last-choice if mica cannot be found.

    If those transistors actually test good, you probably should get down on your knees and give thanks that they were not blown. Changing them is not the worst thing ever, but it is a lot of re-engineering and effort to retrofit.
     
  4. Poasttoastie

    Poasttoastie Member

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  5. Poasttoastie

    Poasttoastie Member

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    Thanks Matt and Watthour, I bought some more transistors for the 1280 off Ebay just in case. I have those being tested now to see if they are good. My Tech guy has been very busy and unable to check them so I do not know I will fair on those yet. I did not see any rips or tears in the mica washers and will be using some Insignia Thermal Compound. It was all I could find locally on the shelf to get. My Mouser order came in and waiting now for some parts from Digi-Key that Mouser did not have. When they do, my tech will be ready then to start the recapping process with it. Has anyone posted a retrofit step by step for the 1280 transistors if it comes to that? I searched but have not found anything on this site yet on the topic. I am still searching though...
     
  6. rcs16

    rcs16 AK Subscriber Subscriber

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    I'd be wondering why my tech guy needs your vs using his own thermal compound without resorting to an unknown entity such as "Insignia Thermal Compound". If you have read these threads you would know what we/I recommend Wakefield #120 comes to mind. Mouser sells a small pack 567-120-SA, which I have included in the STK-0050 kit.
    Mark has shown how he fab'd the replacements, I do not know the exact thread, just need to search, his sx-1280 threads.
     

     

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  7. Poasttoastie

    Poasttoastie Member

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    After 40+ years of doing Electronic repair work, he is basically retired from it but still has his equipment sitting around. He is knocking the dust off his desoldering unit and Soldering iron as a favor to me and going to change out the caps in this SX-1280 that I recently came across. The deal was I buy the parts and send to him and he will furnish his time and expertise to do the job. I will do some more digging as I find time to on the 1280 retrofit . I do not have a 8 to 5 job M-F and sometimes I have to travel great distances with my work with little notice so my computer searching time is very limited by access to the internet where I am and having the time to do it. I will look up the Wakefield #120 and order some. The other Heat sink grease is just what I found locally at a Bestbuy. The closest wholesale or retail Electronic supply store currently is over 70 miles away from me at best.
    Thanks
     
  8. rcs16

    rcs16 AK Subscriber Subscriber

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    one way or the other who ever does the work needs to understand what is involved in a 1280 retrofit.
    Should not have to worry about distance from your parts store, mine is a lot further than 70 miles away
    Mouser Electronics Inc. - 1000 N. Main St., Mansfield, TX 76063.
    I see they even offer USPS international shipping service now. It was $20 for me, in Canada. I usually buy >$100 so we get free FedEx shipping in 2-3 days. What more can you ask for?
     
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  9. Poasttoastie

    Poasttoastie Member

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    I am hoping everything works out with the originals since they are testing good. I think I found the thread you were referring to about the retrofit transistors. It was by Echo wars and not Mark on a SX-1980 transistors which are the same as the 1280. Was the heat sink grease they originally used back then better than what is available today?
    How bad does Canadian customs hit you on the duty tax when you order from inside the U.S.?
     
  10. rcs16

    rcs16 AK Subscriber Subscriber

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    Mouser takes care of customs because we pay HST to them directly. yeah EW & MTF + others have done these mods. go with the original devices and only use the subs if last resort.
    120 compound has been available as long as the Pioneer sx-1280. As you can see not very many even use the compound/mica any more vs the new silpads.
     

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