Got another mtx TA92001.
Botched repair by someone else. Fixed most of the issues I found (d401 had been flipped backwards; confirmed with my functioning 92001)
All output fets removed no shorts found between the open veers . Power supply side operates beautifully. High side 3120 optocouplers also removed.
Powering the amp up on the high side I'm getting 140vdc on both the gate and the source which slowly falls to 122vdc and stays there. On the drain I'm getting 112vdc
Low side of the output shows -115 on gate and source. Drain also shows 112vdc.
This can't be right? What part would fail and cause this? The only thing I can find faulty is one of the output inductors which I have pulled out of circuit to rewind but that shouldn't cause this issue right?
Botched repair by someone else. Fixed most of the issues I found (d401 had been flipped backwards; confirmed with my functioning 92001)
All output fets removed no shorts found between the open veers . Power supply side operates beautifully. High side 3120 optocouplers also removed.
Powering the amp up on the high side I'm getting 140vdc on both the gate and the source which slowly falls to 122vdc and stays there. On the drain I'm getting 112vdc
Low side of the output shows -115 on gate and source. Drain also shows 112vdc.
This can't be right? What part would fail and cause this? The only thing I can find faulty is one of the output inductors which I have pulled out of circuit to rewind but that shouldn't cause this issue right?
At the time I has suspected them of being shorted in some capacity and transmitting the higher than rail voltage to the gate and source legs of the high side.
I think it will be easier to troubleshoot with all 4 of the optocouplers out and the pin 5-6/7 jumped to prevent the outputs from switching on.
All four 3120s are now out of the amp. Same issue as before. With the output mosfets removed, do I need to jump pin 5-6/7?
The amps current condition. D401 measures appropriately in and out of circuit.
Im going to remove the small 63v cap and replace with the approrptaite 35v 1000uF that should be there since the voltage differnetial across the leads is never more than 19v
Im going to remove the small 63v cap and replace with the approrptaite 35v 1000uF that should be there since the voltage differnetial across the leads is never more than 19v
The jumper is to prevent the outputs from switching on. The jumper allows you to judge the condition of the outputs in the circuit. If they are leaking or shorted, you will have DC on the output. If there is no DC, the outputs are typically OK.
Did the capacitor fail (explode). If not, why was it replaced?
The D401 statement is incomplete?
Did the capacitor fail (explode). If not, why was it replaced?
The D401 statement is incomplete?
My next thought is to pull the large silicone encase 10k resistor that supplies 140v to see if I loose the higher than rail voltage from the gate and source?
The previous owner placed that small 63v capacitor there. I don't know why he did that. The previous owner also tried to remove the large rail caps, consequently the solder connection were atrocious. I removed them and intend to correctly solder them back in. He also botched one of the output filter inductors, hence why that is out. (Lots of soldering issues from the PO.)
Diode D401 was flipped backwards. I replaced it with a new diode that appears to test correctly with my DMM in circuit.
By outputs are you referring to the smd A56 and A06 transistors?
Either way I will jump those pins.
There are no output transistors in the amp right now. I pulled them all. On the output side of the amp
No continuity between any of the open veers as well. I jumped pin 5 to pin 6 on all 4 3120 spots. Same issue.
Connect a load across the speaker terminals That should pull the voltage down to 0v across the terminals with no additional current draw. Does it?
Do you still have higher than rail on the output transistors?
Do you still have higher than rail on the output transistors?
Every single one on the high side.
FET 408
FET 406
FET 410
FET 412
FET 402
FET 404
FET 414
FET 416
Worth noting I have 122vdc on all low side drains as well.
FET 408
FET 406
FET 410
FET 412
FET 402
FET 404
FET 414
FET 416
Worth noting I have 122vdc on all low side drains as well.
The missing inductor is causing the problem with not dragging the voltage down. Install a jumper in its place if it can't be soldered back in. Watch for increased current draw.