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Peavey XR 696F - I made a booboo

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  • #16
    I'm struggling to get the larger transistors off the board without damaging the tracks, they are in there tight! So far I've managed to remove and test Q201, Q202, Q214, all of which come up as working on my transistor tester.

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    • #17
      To be honest, I'm not sure what happened here. You connected live to chassis (nasty!) , neutral and earth to power transformer, right? In that case the amp would not have been energized so no risk to the transformer. R273 goes between chassis and power ground ( it I followed it right) so current could only flow if something else was connected. So what was it connected to and did it get damaged? If nothing was connected then it's not clear to me why R273 would blow.
      Experience is something you get, just after you really needed it.

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      • #18
        I connected the transformer live and neutral to the two earths on the power break out board, and the transformer and preamp board earths to live and neutral. The bottom/middle of page 1 of the power board schematic shows the four spade connectors, though there is no longer a double switch, a previous hack job has bridged one of the switches after they fitted a basic non oem switch, which I had been inspecting in the first place before i cocked up the wiring

        This blew the circuit breaker in the house, unsurprisingly. So I unplugged it and put it back in round the right way and powered it up, magic smoke followed shortly afterwards.

        I noticed earlier today one of the large filter caps has flashed over it's leads, there is a scorch mark on PCB and a little chunk of solder had been vaporised. Nothing was connected to the amp when i powered it up, input or output.

        I'm a little out of my depth depth here, but I have at least made some progress

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        • #19
          I'm now as far as removing and testing Q201, Q202, Q214, Q210, Q207, all test as working transistors in my tester.

          When plugged into the bulb limiter, would the faulty components potentially warm up? Or components in the path of a fault? I ask as I plugged the bulb limiter back in and checked all the main transistors for any noticeable heat, Q210 Q207 both warmed enough to notice with my finger tips, the other large transistors all stayed stone cold.

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          • #20
            Originally posted by jondoe View Post
            I'm now as far as removing and testing Q201, Q202, Q214, Q210, Q207, all test as working transistors in my tester.

            When plugged into the bulb limiter, would the faulty components potentially warm up? Or components in the path of a fault? I ask as I plugged the bulb limiter back in and checked all the main transistors for any noticeable heat, Q210 Q207 both warmed enough to notice with my finger tips, the other large transistors all stayed stone cold.
            Was the bulb bright, or bright-ish, when they were getting warm? If the bulb is glowing and the transistors are getting warm I would say that they are suspect. To quote something said often by the smart ones: a tester can show you if a part is bad, but not if it is good, or something like that. It could also be that the driver transistor feeding them (Q215) is bad. So do you have the "A" power module working now? One nice thing about a stereo amp is that if you have one working side you can use it as a reference to debug the non-working channel.

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            • #21
              Originally posted by glebert View Post
              Was the bulb bright, or bright-ish, when they were getting warm? If the bulb is glowing and the transistors are getting warm I would say that they are suspect. To quote something said often by the smart ones: a tester can show you if a part is bad, but not if it is good, or something like that. It could also be that the driver transistor feeding them (Q215) is bad. So do you have the "A" power module working now? One nice thing about a stereo amp is that if you have one working side you can use it as a reference to debug the non-working channel.

              The bulb was bright while they were getting warm, those two transistors have been out and tested, my little component tester identifies them as NPN's, but maybe they are still faulty? Q215 and Q208 were both replaced. Perhaps I should order up replacements for 210/207

              It looks like the 2SC3281's are no longer in production and a pain to get real ones at a reasonable cost. Could I use the 2SC5200 as a replacement? And would I need to change both in the pair? i.e 2SC520+2SA1943

              I have tried using the "working" side as a reference but I can't find any glaring differences in readings from various places on the circuit.

              Thanks!

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              • #22
                Originally posted by jondoe View Post
                The bulb was bright while they were getting warm, those two transistors have been out and tested, my little component tester identifies them as NPN's, but maybe they are still faulty?
                Most testers use a very small voltage to test the transistor junctions, like 5V, and it is possible to have a transistor that seems OK at low voltages and then behaves differently in circuit. In general the advice is to replace all the power transistors together so that they are close-ish to being matched. That can really suck as these are expensive and sometimes hard to find and I know I am afraid that when I put them in the circuit they are just going to smoke. I will let someone else comment on the best available modern transistors to replace those, as I have not replaced those or done the research on them. Usually there is something that is more available that will work fine.

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                • #23
                  I took a chance on some 2SC5200's, they arrived this morning. I removed Q210/Q207 and tested the power board on the light bulb before fitting the new ones, it did not shine brightly. I put in the 2SC5200's, tested it again and the bulb shines brightly as before and they feel a little warm to the touch.

                  I noticed that if I do not connect the HDR100 AC power and plug in both the power amps AC feeds, the bulb does not shine brightly, if I plug HDR100 back in, the bulb shines brightly once more, which I wasn't expecting. If I then remove J202, and leave HDR100 connected the bulb becomes dim again.

                  During more poking around today I found what I think is a faulty component on the jack board, it's SCR200 (SAC187V) on the jack board of the "Mixer Amp B" side, powered by the J202 AC feed. The SCR200 doesn't test the same as the one on the other side of the board, it even felt a little warm while testing on the bulb limiter, so I removed it. I then powered up the board with all AC feeds in place, the bulb blinked and went dim.

                  This might be a red herring, but for the sake of not much money I'll order a replacement and see if that resolves anything. I'm going for a BTA16-600 as a replacement. The board had MAC12M in place and not a SAC187V as shown on the schematic.

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                  • #24
                    I noticed that if I do not connect the HDR100 AC power and plug in both the power amps AC feeds, the bulb does not shine brightly, if I plug HDR100 back in, the bulb shines brightly once more, which I wasn't expecting. If I then remove J202, and leave HDR100 connected the bulb becomes dim again.
                    So HDR100 is the AC for your +/-25V supply and J202 is the AC for the +/-40V supply, right? When you have only one of them hooked up your bulb is dim, but if you hook them both up it is bright, correct? Seems to me like there is a driver or pre-driver transistor (which are run from the 25V) that is pulling those two power transistors (which are on the 40V) on hard. I would try measuring voltages with only HDR100 hooked up, and do the same on the working amp board and look for a difference.

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                    • #25
                      Originally posted by glebert View Post
                      So HDR100 is the AC for your +/-25V supply and J202 is the AC for the +/-40V supply, right? When you have only one of them hooked up your bulb is dim, but if you hook them both up it is bright, correct? Seems to me like there is a driver or pre-driver transistor (which are run from the 25V) that is pulling those two power transistors (which are on the 40V) on hard. I would try measuring voltages with only HDR100 hooked up, and do the same on the working amp board and look for a difference.

                      I'll make a list of the variations I've tested so far;

                      "Mixer Amp 500 watts A" has HDR100 (25v) and J107 (40v)
                      "Mixer Amp 500 watts B" has J202 (40v) - this one has the warm transistors, even after replacing

                      HDR100 = Dim bulb
                      HDR100 + J107 = Dim bulb
                      HDR100 + J202 = Bright bulb
                      J102 = Dim bulb
                      J202 = Dim bulb
                      J102 + J202 = Dim bulb
                      HDR100 + J102 + J202 = Bright bulb

                      I don't have a working amp board as such, I just assumed "Mixer Amp 500 watts A" was the working half of the two circuits

                      Comment


                      • #26
                        Originally posted by jondoe View Post
                        I'll make a list of the variations I've tested so far;

                        "Mixer Amp 500 watts A" has HDR100 (25v) and J107 (40v)
                        "Mixer Amp 500 watts B" has J202 (40v) - this one has the warm transistors, even after replacing

                        HDR100 = Dim bulb
                        HDR100 + J107 = Dim bulb
                        HDR100 + J202 = Bright bulb
                        J102 = Dim bulb
                        J202 = Dim bulb
                        J102 + J202 = Dim bulb
                        HDR100 + J102 + J202 = Bright bulb

                        I don't have a working amp board as such, I just assumed "Mixer Amp 500 watts A" was the working half of the two circuits
                        The HDR100 is supplying 25V to both A and B circuits, right? So you can power up everything except the power transistors (which come off of the J101,J202 AC lines). If you leave J101 and J202 disconnected the A and B circuits should be in the same state. I would measure voltages, starting where the driver section interfaces with the power transistors, and look for a difference between the two sides. If you find a difference, work further up the circuit (i.e. towards the left) and see when you have symmetrical voltages.

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                        • #27
                          Originally posted by glebert View Post
                          The HDR100 is supplying 25V to both A and B circuits, right? So you can power up everything except the power transistors (which come off of the J101,J202 AC lines). If you leave J101 and J202 disconnected the A and B circuits should be in the same state. I would measure voltages, starting where the driver section interfaces with the power transistors, and look for a difference between the two sides. If you find a difference, work further up the circuit (i.e. towards the left) and see when you have symmetrical voltages.

                          That all makes sense, thank you for explaining that. I'd overlooked the fact the 25v was shared on both sides! I will test and report back soon.

                          Comment


                          • #28
                            Originally posted by jondoe View Post
                            ......During more poking around today I found what I think is a faulty component on the jack board, it's SCR200 (SAC187V) on the jack board of the "Mixer Amp B" side, powered by the J202 AC feed. The SCR200 doesn't test the same as the one on the other side of the board, it even felt a little warm while testing on the bulb limiter, so I removed it. I then powered up the board with all AC feeds in place, the bulb blinked and went dim.

                            This might be a red herring, but for the sake of not much money I'll order a replacement and see if that resolves anything. I'm going for a BTA16-600 as a replacement. The board had MAC12M in place and not a SAC187V as shown on the schematic.
                            That SAC187 is part of Peavey's "crowbar" circuit and is a triac for speaker protection. If the amp outputs DC, it turns on the triac and shorts the output to ground. Good for speakers,...... not so much for the amp. They do often permanently short when there is and amp problem. You can run the amp without it for testing, but do not hook up a load/speaker until you verify that there is no DC on the amp's output. After you verify the amp is working and no DC, install the new triac.
                            "Yeah, well, you know, that's just, like, your opinion, man."

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                            • #29
                              Thanks The Dude

                              I'm had a little time to look over the board today, running just the HDR100 connector 25v power. The first thing I noticed were a very hot pair of resistors on the "AMP IC SUPPLY" section (1st page, the very bottom/middle) with the +/-25V rails. R290/R291 were incredibly hot, so much so R290 undersold itself and fell out when touched. I've lifted the legs on both of them now so they are no longer in circuit and aren't melting.

                              Testing at the XR header (to the far right of the HDR100 input) I found the following;

                              -15v rail is -16.4v
                              +15v rail is 13.9v
                              +48v rail is 33v

                              When I get a chance to get back out to the shed I'll take some more measurements.

                              Comment


                              • #30
                                Originally posted by jondoe View Post
                                Thanks The Dude

                                I'm had a little time to look over the board today, running just the HDR100 connector 25v power. The first thing I noticed were a very hot pair of resistors on the "AMP IC SUPPLY" section (1st page, the very bottom/middle) with the +/-25V rails. R290/R291 were incredibly hot, so much so R290 undersold itself and fell out when touched. I've lifted the legs on both of them now so they are no longer in circuit and aren't melting.

                                Testing at the XR header (to the far right of the HDR100 input) I found the following;

                                -15v rail is -16.4v
                                +15v rail is 13.9v
                                +48v rail is 33v

                                When I get a chance to get back out to the shed I'll take some more measurements.
                                Were these taken with cable plugged into XR header? If so I would repeat with it unplugged. Odd the difference in the output of the +/- 15V regulators. If the 48V is still low with XR unplugged I would look at the voltage of the base of Q103, it should be about 48V there.

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