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Crown CE2000 Power amp repair question ...

Discussion in 'Audio' started by Journey11, May 7, 2020.

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  1. Journey11

    Journey11

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    0
    May 23, 2018
    Hello All,
    I am currently rebuilding a Crown CE2000xt power amp that had the typical catastrophic meltdown that is known to occur with these amps. Basically a whole crap load of components get burnt up due to some high overvoltage failure. After replacing about $100 worth of components I found 6 more that needed replacing for another $15.
    But 2 of the components (MBS4993 Silicon Bidirectional Switch Diode Thyristor) I was not able to source new ones. The only thing available was a more robust component with much higher specs all round and that part number is SST131U-600D purchased from Digikey.
    I have attached the amp schematic with a red colored marker of the area where the MBS4993 is working in conjunction with another more robust Triac.

    My question is ... what exactly is this section of the circuit doing here ? And whether or not the more robust replacement I obtained will do the same job as the original according to each components datasheet specs. I am having a funny feeling that the replacement may not work in this config.

    PS>>> After doing another web search for this MBS4993 part, I managed to find a possible source to buy them. I submitted an email for a quote and am waiting to hear back. Apparently there was 8 suppliers that may or may not have them in stock. So if I'M SOL to get these exact replacements, then I will be needing someones advice here on if the more robust SST131U-600 will function properly.
    I hope the diagram is readable ... I had to reduce the file size considerably ... for some reason I kept getting errors trying attach the upload. File size restrictions ??? CrownAmp.jpg

    Thanks in advance,
    Journey
     
  2. bertus

    bertus Moderator

    754
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    Nov 8, 2019
  3. Journey11

    Journey11

    42
    0
    May 23, 2018
    Hi Bertus,
    So I believe both those components are triacs but they are somehow different from each other.
    So you are saying that these two components are there as a protection ? I am going to guess that these 2 triacs (sbs's) will switch on in the direction to ground to shunt any over voltages to ground ? That's pretty much what I'm seeing there.
    I'm still having some trouble finding anyone who has a 4993 in stock ... I found one company that has 4991 and 4992 but the spec for power is only 200 - 300 mW whereas the 4993 is 500 mW. So not sure if a lesser unit will do the trick here.
     
  4. bertus

    bertus Moderator

    754
    268
    Nov 8, 2019
  5. Journey11

    Journey11

    42
    0
    May 23, 2018
    Hi Bertus,
    Thanks for the pointers to the part I was looking for. I managed to get a search hit for a company called digchip and they sent out quote notifications to about 8 Chinese companies that has some stock. So managed to order a couple from China. I looked at the MBS4991's and the power rating was a bit lower than the 4993 so was a bit hesititant to take a chance there. If I wasn't able to source the originals I probably would have gone for it but who knows whether it would have lasted long. Even my gal in Hong Kong couldn't source them and she's pretty good usually. I'll let ya'll know in a few weeks how the repair job went. ie. If it just blew itself to bits again OR up and running ...
    Journey
     
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