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Thread: Peavey XR 696F - I made a booboo

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    Peavey XR 696F - I made a booboo

    After a decent run of small repairs I came upon a Peavey XR 696F with intermittent signal problems, so I bought it as a cheap project to play with. On inspection someone had fudged in a non-oem power switch and fitted a different fuse holder, along with a 12v cooling fan with a bunch of resistors to replace the original 24v. I removed the power amp board/panel and inspected the work, it's rough but functional.

    On reconnecting the transformer to the poweramp board I made a mistake, while referring to the pictures I'd taken of the wiring I didn't realise the phone had rotated the image 180 degrees, so I ended up plugging the L/N mains wires into the earth tabs and the earth into the L/N tabs. The magic smoke followed shortly after powering it back on, followed even closer by swearing and self flagellation.

    I can only see one small burnt out resistor on the power amp board (R273), but I don't suppose I've been that lucky. I've tested the transformer on it's own, it's not suffered any damage, but I don't no where to start with the power board/preamp board. I guess I should concentrate on the power board for now and worry about the preamp board later?

    Any advice for this idiot is welcome, I'm feeling pretty special today!

    Pvy XR696F.zip

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    Last edited by jondoe; 11-07-2019 at 01:58 PM. Reason: added detail

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    I've done worse. I would focus on voltage rails from the power supply, especially if it is a separate board. Unplug whatever you can, and if you have a variac and/or light bulb limiter use those to bring it up.

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    Quote Originally Posted by glebert View Post
    I've done worse. I would focus on voltage rails from the power supply, especially if it is a separate board. Unplug whatever you can, and if you have a variac and/or light bulb limiter use those to bring it up.
    This is the worst thing I've done for a little while, another free life lesson

    So far, I've replaced R273 as I had one on a scrap board. I've tested connecting AC to HDR100 (1st page, top left) which is the power supply for the preamp board side. I plugged in preamp board and it lights ups, the effects board initialises and no magic smoke, it passes signal to the monitor output, so that's probably OK. That leaves the two high/low voltage sides for the power amp.

    I have no variac and I should probably make limiter bulb, I've got away without one for a long time

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    Last edited by jondoe; 11-07-2019 at 04:41 PM.

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    I have built a light bulb limiter as it blew another plug fuse (i tried the two high voltage feeds), it blew R273 again and let lots of smoke out, I think from Q103 from what I could tell. With a 60w bulb in the limiter it lights up bright if you plug in either of the two high voltage, I guess I've found a rough area of my problem

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    Supporting Member The Dude's Avatar
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    I'm admittedly old and blind, but can't for the life of me find R273 on the schematic. Anybody else?

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    Quote Originally Posted by The Dude View Post
    I'm admittedly old and blind, but can't for the life of me find R273 on the schematic. Anybody else?
    It is in the power module pdf, left edge of the page. Top of vertical section C.

    Click image for larger version. 

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    Quote Originally Posted by The Dude View Post
    I'm admittedly old and blind, but can't for the life of me find R273 on the schematic. Anybody else?
    Far left side of schematic by edge between c and d markings on schematic side.

    Q103 is for 48v phantom voltage.

    nosaj

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    Thanks fellas!

    That resistor is between 2 different grounds. I'd be looking for a burnt trace somewhere and quite possibly more.

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    Gah, I didn't say where R273 was on the schematic, sorry about that, it's well hidden over there.

    I couldn't find a burnt trace/track anywhere on the board, but I'll go over it again with a magnifying glass and a bright light, just to be sure. I'll take the heat sinks off again and have a look around. Those big transistors look like a pain to remove and place back, I hope I haven't popped too many of them!

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    So far we the dead transistors I've found are;

    Q216 (A1387)
    Q208 (C4793)
    Q115 (A1837)
    Q221 (A1837)
    Q100 (C4793)

    It's a little cold out in the shed tonight so I've left it for now and I've ordered up a bunch of the above. I will test some more parts tomorrow

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    I have so far replaced

    Q215
    Q208
    Q121
    Q221

    Q100 was not faulty when tested on a component tester, so I've put that back for now.

    I've plugged her back into the mains with the bulb limiter and tried the AC feeds for high voltage side one by one. With JC107 plugged it I get a brief glow and then a tiny faint glow. When I plug in JC202 I get a strong constant bright light.e bulb limiter and tried the AC feeds for high voltage side one by one. With JC107 plugged it I get a brief glow and then a very faint glow. When I plug in JC202 I get a strong constant bright light.

    I'm still learning but I assume that one half of the circuit (JC107) might be OK now, the other (JC202 side) still has a short/dead component?

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    When you connect JC202 and the brighter light comes on, you have disconnected JC107?
    Then yes, the JC107 circuit may be ok, and JC202 side still has a problem.

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    Correct, I tried them both independently of each other the JC202 shines brightly. Thanks for confirming that I take it the light bulb will go some way to protect the circuit from further damage?

    Looks like I've been 50% lucky so far

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    Quote Originally Posted by jondoe View Post
    I take it the light bulb will go some way to protect the circuit from further damage?
    Generally, yes. As I understand it the magic of the light bulb is that its resistance goes up when it gets hot, so when current is high most of the voltage drops across the bulb. Depending on the wattage of the bulb it may or may not protect it fully (high wattage bulbs will give less protection). I usually have a few different wattage bulbs available to choose my level of protection.

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    Quote Originally Posted by glebert View Post
    Generally, yes. As I understand it the magic of the light bulb is that its resistance goes up when it gets hot, so when current is high most of the voltage drops across the bulb. Depending on the wattage of the bulb it may or may not protect it fully (high wattage bulbs will give less protection). I usually have a few different wattage bulbs available to choose my level of protection.
    Good to know. I searched all over the house and only found a 60w incandescent, hopefully that will tide me over.

    As JC202 supplies AC for the high and low voltage side of that circuit, do you think it would be safe to test each supply idividually? That is, supply AC power to each bridge rectifier within the circuit idividualy by removing the AC feed (temporarily) from the plug from the transformer. This might allow me to further isolate the location of the problem, or is that a stupid idea

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    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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    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.

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    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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    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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    Quote 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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    Quote 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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    Quote 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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    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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    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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    Quote 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

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    Quote 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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    Quote 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.

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    Quote 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.

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    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.

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    Quote 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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    Quote Originally Posted by glebert View Post
    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.

    These were taken without the XR header plugged in, sorry I should have mentioned that. Q103 measured 33v/85v/47v (pins 1, 2, 3, which I think is B, C, E). When I tested the Voltage regulators VR100/VR101, I noticed the ground pins all have approx -1.3v on them, in fact -1.3 is volts seems to appear on the grounds on many parts on the board.

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    Quote Originally Posted by jondoe View Post
    These were taken without the XR header plugged in, sorry I should have mentioned that. Q103 measured 33v/85v/47v (pins 1, 2, 3, which I think is B, C, E). When I tested the Voltage regulators VR100/VR101, I noticed the ground pins all have approx -1.3v on them, in fact -1.3 is volts seems to appear on the grounds on many parts on the board.
    It looks like there are essentially two ground domains, one called GNDA and one called FGND, but they should be connected via JMP1 and JMP2. Adding 1.3V to each of the 15V rails would make those voltages seem right. The emitter voltage of Q103 seems way off, I would expect it to be just a little below the base voltage, but that transistor shouldn't screw up overall operation since it is just for phantom power. Pins 1,2,3 are BCE, but since you said you measured 33V at the XR header then it seems like the order you recorded them in might be reversed.

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    Last edited by glebert; 11-15-2019 at 10:12 PM.

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    If the amp puts out DC, then the thing is already blown. The triac crowbar shorts the output. That saves your expensive speakers from cathcing fire, and it also SHOULD blow the main fuse/breaker on the amp. A hard core power down.

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    Quote Originally Posted by glebert View Post
    It looks like there are essentially two ground domains, one called GNDA and one called FGND, but they should be connected via JMP1 and JMP2. Adding 1.3V to each of the 15V rails would make those voltages seem right. The emitter voltage of Q103 seems way off, I would expect it to be just a little below the base voltage, but that transistor shouldn't screw up overall operation since it is just for phantom power. Pins 1,2,3 are BCE, but since you said you measured 33V at the XR header then it seems like the order you recorded them in might be reversed.
    I took the measurements of the 15 volt rails using FGND and they came out at a more respectable 15.2/-15v.

    I've double checked Q103 on the board and traced the tracks from the legs to the next component on the schematic, 33v/85v/47v was correct, I don't think I have them reversed. I found R119 (100k) was reading 3ohms out of circuit and replaced it. Further back down the line D104/107 are showing 87v leading to R110. R110/R116 look like a voltage divider, would it be a good idea to remove both the resistors and test them out of circuit? Below is a note of some of the voltage readings I've taken around the Q103

    Click image for larger version. 

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    Quote Originally Posted by jondoe View Post
    I found R119 (100k) was reading 3ohms out of circuit and replaced it.
    This is very strange. Resistors almost never short. Is it's body marked as a 100K resistor?

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