I have soaked transistors with plain Iso Alcohol, it worked.
82 V DC at output means big trouble, see the transistors and drive circuit with a meter, check the supply and trace it to the transistors.
Unfortunately, some computer CPU thermal compounds are known to be adhesive, who puts silicon pads AND thermal compound?
That means somebody has attempted repairs, maybe.
That is another can of worms.
You may find references to stuck coolers in computer forums, the compounds applied with a syringe are famously sticky, and maybe you find how they were removed.
I would check if the transistors are blown, and as there seem to be SMD parts, it may not be worth the effort to fix it up, as it is it came free of cost.
Blown transistors means you cut off the leads, remove PCB, and use brute force if needed to remove the stuck parts.
And that will still need finding out what blew them in the first place.
82 V DC at output means big trouble, see the transistors and drive circuit with a meter, check the supply and trace it to the transistors.
Unfortunately, some computer CPU thermal compounds are known to be adhesive, who puts silicon pads AND thermal compound?
That means somebody has attempted repairs, maybe.
That is another can of worms.
You may find references to stuck coolers in computer forums, the compounds applied with a syringe are famously sticky, and maybe you find how they were removed.
I would check if the transistors are blown, and as there seem to be SMD parts, it may not be worth the effort to fix it up, as it is it came free of cost.
Blown transistors means you cut off the leads, remove PCB, and use brute force if needed to remove the stuck parts.
And that will still need finding out what blew them in the first place.
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Make sure you investigate P1 resistance setting. If the pot's adjusted resistance is too low, the amp will peg with -80V on the output.
I appreciate the desire to be able to remove the output transistors, but you could try to troubleshoot without removal. It's conceivable it's something in earlier stages.
I appreciate the desire to be able to remove the output transistors, but you could try to troubleshoot without removal. It's conceivable it's something in earlier stages.
P1 was my thought as well.
When measuring, as best I can from leads above, there is no difference in the resistance.
And in order to remove P1, I need the circuit board off the heatsink.
Which, brings me right back to the transistors that are stuck…
When measuring, as best I can from leads above, there is no difference in the resistance.
And in order to remove P1, I need the circuit board off the heatsink.
Which, brings me right back to the transistors that are stuck…
![DSCN0308[1].JPG](/community/data/attachments/1085/1085754-f74caed45d1f409bbc9402f8f4759971.jpg?hash=90yu1F0fQJ)
Why not test the transistors in circuit to start?
Also have you checked both power supply voltages, and the fuses?
Also have you checked both power supply voltages, and the fuses?
Hey. I did test all the output transistors in circuit. They are all good, and the same, as are the emitter resistors. But the other on the board….
What are the DC voltages at the output device gates?
How about DCV at the gate of Q2? The output devices may all be ok.
How about holding off on the demolition for now, and thinking instead.
Wonder if C3 or Z2 may be shorted.
What about switch TB101, it appears to turn off the input stage current sources.
Who knows what that is supposed to be for, maybe a thermal shutdown?
How about DCV at the gate of Q2? The output devices may all be ok.
How about holding off on the demolition for now, and thinking instead.
Wonder if C3 or Z2 may be shorted.
What about switch TB101, it appears to turn off the input stage current sources.
Who knows what that is supposed to be for, maybe a thermal shutdown?
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I’ll have to confirm voltages when I get home on Monday night. But from memory, out of the power supply I was getting 82 and 96? Should be 60 and 73? Those voltages were unloaded…
And I’m back home 🙂
About to check the bits and measure voltages as suggested.
Tricky getting in there, as there is a copper heatsink on top of Q2. I’ll have to see what tge gate is connected to a measure there. Same with checking for shorts at C3 and Z2
About to check the bits and measure voltages as suggested.
Tricky getting in there, as there is a copper heatsink on top of Q2. I’ll have to see what tge gate is connected to a measure there. Same with checking for shorts at C3 and Z2
Can’t check C3 on its own, but I can check across C4, which is in parallel with C3, and I’m not reading a short. Also not reading a short across Z2. And I’m measuring 0.687v on Z2. I have to reassemble the amp, and hook the amp board back into the PS to check voltage at Q2 gate.
Reassembling the amp, putting the PS board back in and hooking up the amp boards. Was going to confirm the B+/B- I listed above.
As I had a busy weekend with the kids, and had a long day at work, thought I should do it tomorrow, when I’m not so tired. Not a fan of the magic blue smoke 🙂 Turning over a new leaf of semi-responsible behavior…
Will check the voltages, as well as the gate voltage on Q2. Will also check the resistance of the thermistors.
TB101, is eluding me though? Can’t find it on the schematic?
Thanks for all your help with this!
As I had a busy weekend with the kids, and had a long day at work, thought I should do it tomorrow, when I’m not so tired. Not a fan of the magic blue smoke 🙂 Turning over a new leaf of semi-responsible behavior…
Will check the voltages, as well as the gate voltage on Q2. Will also check the resistance of the thermistors.
TB101, is eluding me though? Can’t find it on the schematic?
Thanks for all your help with this!
Right, that is what I seen that was weird and interesting
seemed to turn off the current sources.
What the heck.
Very generalized because every amp is different.
but hard rail on output. usual suspects. bias pot lost
or current sources either actual semiconductors or connections
in those circuits . or failed to a short outputs.
Voltages update…
Using speaker ground.
On the right channel, I am getting 123vdc from the 60v b+, and 137vdc from the 73vdc b+
On the left channel, I am getting -7vdc from the 60vdc b+, and 4.28vdc from the 73vdc b+
Checking voltage at gate of Q2.
I am seeing -38vdc on the right channel, and -7vdc on the left channel.
Hope this makes more sense to you guys than it does to me 🙂
Using speaker ground.
On the right channel, I am getting 123vdc from the 60v b+, and 137vdc from the 73vdc b+
On the left channel, I am getting -7vdc from the 60vdc b+, and 4.28vdc from the 73vdc b+
Checking voltage at gate of Q2.
I am seeing -38vdc on the right channel, and -7vdc on the left channel.
Hope this makes more sense to you guys than it does to me 🙂