I've got this amp on the bench which isnt powering up totally well. I pulled it out of the sync, and found Q272 output, and IRF9540 shorted across legs 2&3, and 180 ohms across Legs 1-2.
I clipped the shorted IRF9540, but the amp still fails to power up. It does pulse power-up for about 1/4 second, but that is barely enough time for any troubleshooting. The PS is probably in good shape at this point.
In looking to find further faults, I'd like to be able to troublshoot this amp is a semi-powered on state. Is there anything I can do to let the PS run while connected?
I clipped the shorted IRF9540, but the amp still fails to power up. It does pulse power-up for about 1/4 second, but that is barely enough time for any troubleshooting. The PS is probably in good shape at this point.
In looking to find further faults, I'd like to be able to troublshoot this amp is a semi-powered on state. Is there anything I can do to let the PS run while connected?
Perry,
It barely has enough time to power-up. I basically only see signal on the gates of the PS fets for an extremely quick shot which is not enough time for my FLuke to stabilize any readings (not even rail voltage). If there was a way, like isolating and grounding pin 16 of the TL494, then I could proceed.
It barely has enough time to power-up. I basically only see signal on the gates of the PS fets for an extremely quick shot which is not enough time for my FLuke to stabilize any readings (not even rail voltage). If there was a way, like isolating and grounding pin 16 of the TL494, then I could proceed.
Nope. Tight spot. better readings now
Pin 1: 0.003
Pin 2: 4.97
Pin 3: 0.062
Pin 4: 4.97
Pin 5: 1.464
Pin 6: 3.644
Pin 7: 0
Pin 8: 13.51
Pin 9: 0
Pin 10: 0
Pin 11: 13.51
Pin 12: 13.51
Pin 13/14/15: 4.97
Pin 16: 3.729
Another strange thing I notice it, if I leave the amplifier powered off for several minutes, the first time I power it back on it will go alright. As soon as I power cycle it wont turn back on. Its almost as if leaving it powered off clears it's 'memory' and allows one time power-on. I also confirm, that if I drain the rails then the amp will power once as well.
Pin 1: 0.003
Pin 2: 4.97
Pin 3: 0.062
Pin 4: 4.97
Pin 5: 1.464
Pin 6: 3.644
Pin 7: 0
Pin 8: 13.51
Pin 9: 0
Pin 10: 0
Pin 11: 13.51
Pin 12: 13.51
Pin 13/14/15: 4.97
Pin 16: 3.729
Another strange thing I notice it, if I leave the amplifier powered off for several minutes, the first time I power it back on it will go alright. As soon as I power cycle it wont turn back on. Its almost as if leaving it powered off clears it's 'memory' and allows one time power-on. I also confirm, that if I drain the rails then the amp will power once as well.
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Sorry I'm probably not explaining this very well. When the rail caps are completely discharged, the amp will power on just one time. When it does, it will play and act correctly from everything I measure.
TL494 on first cold-boot (Drained rails)
Pin 1: 0.004
Pin 2: 4.97
Pin 3: 0.065
Pin 4: 0.052
Pin 5: 1.482
Pin 6: 3.692
Pin 7: 0
Pin 8: 12.88
Pin 9: 4.92
Pin 10: 4.92
Pin 11: 12.85
Pin 12: 12.86
Pin 13/14/15: 4.96
Pin 16: 3.569
If I remove REM, and then re-apply within about 1 minute, the amp powers on in protection with no rail voltage. The TL494 shows the following:
TL494
Pin 1: 0.003
Pin 2: 4.97
Pin 3: 0.062
Pin 4: 4.97
Pin 5: 1.464
Pin 6: 3.644
Pin 7: 0
Pin 8: 13.51
Pin 9: 0
Pin 10: 0
Pin 11: 13.51
Pin 12: 13.51
Pin 13/14/15: 4.97
Pin 16: 3.729
*Notice Pin 4, 9, and 10.
The only two ways I can get the amp to power on from this point is
1: Allow the amp to sit for awhile so that trace voltages are naturally reduced
2: Drain the stagnant rail voltage with a resistor
The above is all with Q704 in-circuit. If I lift Q704, I can power the amp on-off every time without protection issues. I presume this circuit is something to do with the thermistors?
TL494 on first cold-boot (Drained rails)
Pin 1: 0.004
Pin 2: 4.97
Pin 3: 0.065
Pin 4: 0.052
Pin 5: 1.482
Pin 6: 3.692
Pin 7: 0
Pin 8: 12.88
Pin 9: 4.92
Pin 10: 4.92
Pin 11: 12.85
Pin 12: 12.86
Pin 13/14/15: 4.96
Pin 16: 3.569
If I remove REM, and then re-apply within about 1 minute, the amp powers on in protection with no rail voltage. The TL494 shows the following:
TL494
Pin 1: 0.003
Pin 2: 4.97
Pin 3: 0.062
Pin 4: 4.97
Pin 5: 1.464
Pin 6: 3.644
Pin 7: 0
Pin 8: 13.51
Pin 9: 0
Pin 10: 0
Pin 11: 13.51
Pin 12: 13.51
Pin 13/14/15: 4.97
Pin 16: 3.729
*Notice Pin 4, 9, and 10.
The only two ways I can get the amp to power on from this point is
1: Allow the amp to sit for awhile so that trace voltages are naturally reduced
2: Drain the stagnant rail voltage with a resistor
The above is all with Q704 in-circuit. If I lift Q704, I can power the amp on-off every time without protection issues. I presume this circuit is something to do with the thermistors?
Perry,
You are on to something. Front Left channel has at most ~22vDC across terminals when the amp wont power up. I monitored the voltage for a few minutes, and it slowly drops down. Once the voltage hits <2vDC, the amp powers up without me having to re-apply any power (Constant power, rem and ground).
Whats strang is, I repaired the FR channel, and this voltage is on FL.
You are on to something. Front Left channel has at most ~22vDC across terminals when the amp wont power up. I monitored the voltage for a few minutes, and it slowly drops down. Once the voltage hits <2vDC, the amp powers up without me having to re-apply any power (Constant power, rem and ground).
Whats strang is, I repaired the FR channel, and this voltage is on FL.
It will power up as the dummy load will discharge the caps (quickly, the woofer will punch once on power-off).
Off the board, I found Q144 measuring 9kohms between legs 2&3. Its a C2344E TO92 transistor. I pulled it, and the amp powers on/off correctly with no voltage on the speaker terminals.
Off the board, I found Q144 measuring 9kohms between legs 2&3. Its a C2344E TO92 transistor. I pulled it, and the amp powers on/off correctly with no voltage on the speaker terminals.
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