Without the resistor installed the voltage on pin 4 when it starts to cut is +2.9 volts.
With the resistor installed it held steady at +0.006 volts.
I have not tried using a heat gun. I'll try it now.
With the resistor installed it held steady at +0.006 volts.
I have not tried using a heat gun. I'll try it now.
It definitely didn't like the heat gun. I'm not a hundred percent sure but the area circled in yellow seemed to be sensitive to the heat. The area in green is a possibility as well but can't be certain as the amp was already shutting on and off at that point.
As I was saying it definitely didn't like the heat gun as the amp no longer powers up at all now. It is shutting down my power supply. It also shuts the power supply down with no power being connected to the remote wire.
As I was saying it definitely didn't like the heat gun as the amp no longer powers up at all now. It is shutting down my power supply. It also shuts the power supply down with no power being connected to the remote wire.
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It blew one of the PS Fets. The same one it had blew before on the left side of the board (side with the yellow circle in the above photo). I pulled it and tried to power the amp up, it immediately blew another PS Fet on that same side of the board. I pulled all of PS Fet's on that side of the board. It is no longer shutting down my power supply.
MPSA06 voltage:
Right:
Leg 1: -0.00
Leg 2: -0.00
Leg 3: +8.23
Left:
Leg 1: +6.65
Leg 2: +7.34
Leg 3: +8.16
Right:
Leg 1: -0.00
Leg 2: -0.00
Leg 3: +8.23
Left:
Leg 1: +6.65
Leg 2: +7.34
Leg 3: +8.16
The right side doesn't look like it has any drive. If one bank of FETs has no drive, it can cause the other bank to fail.
Until you find the fault, I'd suggest using a low value fuse (5 or 10 amps) to help protect the FETs. Even with a low value fuse, they can overheat and fail if not clamped to the heatsink.
Until you find the fault, I'd suggest using a low value fuse (5 or 10 amps) to help protect the FETs. Even with a low value fuse, they can overheat and fail if not clamped to the heatsink.
I have had it clamped to the heatsink this whole time. It is blowing the FETs with them clamped(almost instantly). I tried using a 10 amp fuse as you suggested but the fuse lasts about 2 seconds before it blows.
A current limiter would help. Do you have an old car headlamp to use as one? For someone who doesn't have a 50-100w 2 ohm resistor to use as a limiter, I generally recommend both filaments (in parallel) of an H6054 but any car headlamp should work.
As a side note, the limiter won't work with the old orion amps that were self oscillating (no TL594).
Did you find why the driver transistors were getting no drive?
Shorting the emitter to the collector of the standing 6488 should allow it to power up but it will not produce rail voltage. You should be able to check for drive pulses at the A06.
As a side note, the limiter won't work with the old orion amps that were self oscillating (no TL594).
Did you find why the driver transistors were getting no drive?
Shorting the emitter to the collector of the standing 6488 should allow it to power up but it will not produce rail voltage. You should be able to check for drive pulses at the A06.
I powered up the amp here through a limiter to make sure it would, it did.
While I had it on the bench, I tried tracing the drive as I suggested you do. To test the drive up to the MPSA06, you will have to remove the transistor (which you will likely do to test it, anyway). The drive simply goes from pins 9 and 10 of the 494 through a 2.2k ohm resistor then to the bases of the driver transistors.
Shorting pins 2 and 3 of the 6488 will prevent voltage from reaching the collectors of the MPSA06 driver transistors. You're just trying to determine why you have no drive signal reaching the base of the A06, at this point.
While I had it on the bench, I tried tracing the drive as I suggested you do. To test the drive up to the MPSA06, you will have to remove the transistor (which you will likely do to test it, anyway). The drive simply goes from pins 9 and 10 of the 494 through a 2.2k ohm resistor then to the bases of the driver transistors.
Shorting pins 2 and 3 of the 6488 will prevent voltage from reaching the collectors of the MPSA06 driver transistors. You're just trying to determine why you have no drive signal reaching the base of the A06, at this point.
Amp powers up for a couple of minutes when it is cold then shuts down. When it is powered up I do have voltage at the MPSA06 drivers.
When it shuts down there is no voltage on pins 9 and 10 of the 494.
When it shuts down there is no voltage on pins 9 and 10 of the 494.
Pin 4 going high will stop the IC from producing pulses on 9 and 10.
Previously, you were having a problem of having drive pulses on one set of drivers but not the other. That has nothing to do with the output of the IC. There has to be another reason for it.
Previously, you were having a problem of having drive pulses on one set of drivers but not the other. That has nothing to do with the output of the IC. There has to be another reason for it.
I'm at a complete loss as to what could be driving the voltage up on pin 4.
Best I can tell, pin 14 drives pin 4 (attached a photo of the trace). The only things in that circuit are one electrolytic cap and one tantalum cap(see second photo). Those have both been replaced. Do you think it is possible one of those is causing it?
Best I can tell, pin 14 drives pin 4 (attached a photo of the trace). The only things in that circuit are one electrolytic cap and one tantalum cap(see second photo). Those have both been replaced. Do you think it is possible one of those is causing it?
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Yes it did. The heat gun is what put the amp in the state it is in now. Which is having to power it using the resistor you suggested to limit the current to keep the PS FETs from blowing. Also having no voltage on legs 1 and 2 of the MPSA06's, no voltage on pins 9 and 10 of the 494 and the on pin 4 of the 494 being too high.
I'm not a 100% certain which area was effected by the heat gun. The area that seem to be most effected, that I circled in yellow in post #142, I can find nothing reading out of specs.
I'm not a 100% certain which area was effected by the heat gun. The area that seem to be most effected, that I circled in yellow in post #142, I can find nothing reading out of specs.
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If pin 4 is too high, connect it to pin 7 again and get it back to where it was.
Heat shouldn't cause the amp to malfunction. Even if that's not the only problem, it's something that needs troubleshooting. You may have to use something like a piece of cardboard to block the heat from heating everything in the area to narrow down what's so sensitive.
Heat shouldn't cause the amp to malfunction. Even if that's not the only problem, it's something that needs troubleshooting. You may have to use something like a piece of cardboard to block the heat from heating everything in the area to narrow down what's so sensitive.
The 10k resistor is still on pins 4 and 7. Should I remove it and put a jumper wire on it or try going to a lower ohm resistor?
I solved the power imbalance that was going on which was causing the PS FETs to overheat. I had pulled the MSPA06's and the MSPA56's to test them. They tested good so I tested the pads for voltage, while I had them out of circuit. Found voltage on pad 2 of the left MSPA06 driver. Something conductive was on the board in that area. Not sure was it was as it wasn't visible. Cleaning the area removed it.
I also pulled the 494 cleaned that area of the board and replaced it with a new one. Pin 4 voltage is still high. I have installed the jumper back on it. I'm still at a complete loss as to what could possibly be causing it. Do you have any suggestions on what I should check or do next?
I also pulled the 494 cleaned that area of the board and replaced it with a new one. Pin 4 voltage is still high. I have installed the jumper back on it. I'm still at a complete loss as to what could possibly be causing it. Do you have any suggestions on what I should check or do next?
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