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Trace Elliot 7215 SMC GP7 Bass Amp

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  • Trace Elliot 7215 SMC GP7 Bass Amp

    Hello and first time poster here so thank you for having me here.
    I recently purchased this trace elliot amp with an output issue. It had power but nothing so after some inspection I found the 2 glass fuses missing. After replacing them and turning the amp on ot blew them straight away hence why I'm here in need of some help. After some testing I found the large capacitors have tested fine but the BUZ901P mosfets are letting current though even after being drained so I'm looking at these as a possibility for the short?? I could be wrong so please do fire some ideas around. I'm not 100 confident with terminology or components but I would like to try get this fixed and back working.
    I cannot find any BUZ901P mosfets and I have seen a few topics on here but thought I would post a fresh topic to help me and possibly others that still struggle.
    thank you for reading
    Sam
    Attached Files

  • #2
    Sounds like you have some shorted FET devices. Presumably you will have to replace all of them, check the 1k gate resistors to see if they are blown, I'd check D2 and D3 and Z1 and Z2 for shorted devices too. I would also build a light bulb limiter to work on this so that you can power up and check for high current without blowing fuses or your transformer.

    Doing some digging looks like those BUZ devices are lateral mosfets, and that there aren't many (any?) lateral devices being made anymore, but not sure, maybe someone else with more knowlege will chime in.

    Here's the service manual, 300 watt FET power amp schematic is on page 15.
    Attached Files
    Last edited by glebert; 09-21-2022, 10:57 PM.

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    • #3
      Here's the service manual.

      https://usermanual.wiki/Collections/...anual.pdf.html

      If you have shorted FET's, the original parts are NLA. You'll have to try to find a workable substitute. Also note that all of the FET's are not BUZ901P. Half are the BUZ906P. Some are N-channel and some P-channel.

      Edit: glebert snuck in while I was hunting and typing.
      "Yeah, well, you know, that's just, like, your opinion, man."

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      • #4
        Here's an entire thread on those FET's that discusses substitution and circuit modification

        https://music-electronics-forum.com/...p-replacements
        "Yeah, well, you know, that's just, like, your opinion, man."

        Comment


        • #5
          Thank you for the reply. Have to bear with me on the terminology but saw Mars amp repair has done this successfully and a bit more explanation with pictures would be great (I don't really understand how he achieved it) lol. I will build a light bulb limiter and get back on how to do some further testing. I have had a probe about and the 901p and 906 all are showing power through them even after a reset before activating the gate so my guess is that these have failed. As for anything else I'm unsure what I'm looking at. Infront of them are some 10p orange capacitors and each one of them has a different reading so not sure if these would need changing also?

          Comment


          • #6
            Don't worry at all about caps for now unless one is shorted.

            It sounds like you are a bit new to amp repair, I would say this is a pretty tough project to cut your teeth on. I've fixed hundreds of amps and personally I wouldn't do it because it wouldn't make financial sense. There are guys who are better than me that might have a different opinion. My concern would be that even if I got it working I really wouldn't trust it to stay working.

            Another option would be to replace the power amp section with a class D amp module. Unfortunately your rail voltage is probably a little too high to use the $20 IRS2092 modules on Ebay, and would have to go up to the ones that use 60-80V rails, those are more like $65. Some people have had luck doing this conversion, mine has been mixed. Also, IIRC on the Trace amps the voltage rectification is on the module with the FET devices, so you can't just pull it out completely to put in something else. There may be some class D modules that take AC from the transformer but they are harder to find.

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            • #7
              I am very new to amp repair but not soldering. If I could find someone in the UK I could send it to that I know could have it sorted would be more than happy. Also if there was a direct replacement to swap that would be even better.

              I do have a working 715 GP7 with a bipolar board inside. would it be safe to put that board onto the 7215 and make sure its just a fault with the power side of things?

              Sorry for all the questions just want to try save this from the scrap yard as I love the 7215 sound

              Comment


              • #8
                There are some very qualified UK techs here. Hopefully one of them will chime in. My first step would be to actually check the FET's to see if any are shorted.
                "Yeah, well, you know, that's just, like, your opinion, man."

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                • #9
                  This company in the UK is supposably developing an upgraded drop in amp module for these amps. Sounds like they are way behind schedule, but maybe you could offer to be a beta tester for them. If nothing else they might know of someone who could fix yours or give you some tips.

                  http://www.rsdsound.co.uk/product/re...r-300w-mosfet/

                  Comment


                  • #10
                    Originally posted by The Dude View Post
                    There are some very qualified UK techs here. Hopefully one of them will chime in. My first step would be to actually check the FET's to see if any are shorted.
                    Thanks for that. Hopefully someone from the UK might pick this up and be able to guide or help save it.
                    I discharged the fets before testing them but i found that on source and drain i qas getting a voltage of around 0.4 before i even activated the gate? Im guessing that means thats kaput as far as i can understand?

                    Comment


                    • #11
                      These are the forerunners to the Ashdown bass amps.
                      Before proceeding any further perhaps you should try Black Magic Amplifiers . I think the boss posts here occasionally https://bmamps.com/v01/

                      Mick Bailey (another member here ) is in the UK but I don't know how to get in touch with him.

                      here's some reading for some re the T03 versions ..http://www.exicon.info/news/end-of-a...teral-mosfets/

                      BUZ 901P - 200v 8amps N-Channel = ECX10N20
                      BUZ 906P- 200v 8amps P-Channel = ECX10P20​

                      And the source still has prices on them https://www.profusionplc.com/parts/ecx10p20

                      For the hard core
                      Attached Files
                      Last edited by oc disorder; 09-26-2022, 06:25 AM.

                      Comment


                      • #12
                        Originally posted by oc disorder View Post
                        These are the forerunners to the Ashdown bass amps.
                        Before proceeding any further perhaps you should try Black Magic Amplifiers . I think the boss posts here occasionally https://bmamps.com/v01/

                        Mick Bailey (another member here ) is in the UK but I don't know how to get in touch with him.

                        here's some reading for some re the T03 versions ..http://www.exicon.info/news/end-of-a...teral-mosfets/

                        BUZ 901P - 200v 8amps N-Channel = ECX10N20
                        BUZ 906P- 200v 8amps P-Channel = ECX10P20​

                        And the source still has prices on them https://www.profusionplc.com/parts/ecx10p20

                        For the hard core
                        Thank you ever so much for the reply. Really appreciate your time and input and I will try get in touch with the following above. Its not easy trying to save these old machines but it's got to be done as I love the sound they produce

                        Comment


                        • #13
                          Originally posted by Whiteey86 View Post
                          I discharged the fets before testing them but i found that on source and drain i qas getting a voltage of around 0.4 before i even activated the gate?
                          Sorry but you donīt "discharge Fets", they donīt create or store voltage and not sure what you mean by activating a gate or what result/change it would make.

                          Juan Manuel Fahey

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