Im a little stumped on this amp. Powers up but will not play audio at speaker terminals. Bias is not working at all for either channel. Right channel stays at 0vDC across emitters and no amperage change no matter where I set the pot. Similar on the left channel as there is no controllability, but sometimes it will have some voltage across emitters. Left channel seems to have some floating vDC on it, sometimes.
First I changed out all the 10uf caps on the main board as they had some leakage. Then I wicked and re-soldered all driver/ridsing boards.
Voltages look to be -ok- on the legs of the outputs. I see good rail and regulated voltages, but the left channel seems to have vDC of drift on the speaker terminals. Maybe 1vDC.
Mostly the amp will draw 0.25A, other times it will draw more like 0.75A at idle. When it draws higher amperage, the left channel voltage across emitters goes up to 0.005vDC or a little more, even with the bias pot set to full CCW.
I looked through he 200DSM page and tested all the components highlighted on both of the driver boards. The driver boards this amp is using are identical to the first two large images of the 200DSM page.
Any clue to what I may be missing? Im thinking this amp is muting, but the voltageDC and bias is I believe my first step.
First I changed out all the 10uf caps on the main board as they had some leakage. Then I wicked and re-soldered all driver/ridsing boards.
Voltages look to be -ok- on the legs of the outputs. I see good rail and regulated voltages, but the left channel seems to have vDC of drift on the speaker terminals. Maybe 1vDC.
Mostly the amp will draw 0.25A, other times it will draw more like 0.75A at idle. When it draws higher amperage, the left channel voltage across emitters goes up to 0.005vDC or a little more, even with the bias pot set to full CCW.
I looked through he 200DSM page and tested all the components highlighted on both of the driver boards. The driver boards this amp is using are identical to the first two large images of the 200DSM page.
Any clue to what I may be missing? Im thinking this amp is muting, but the voltageDC and bias is I believe my first step.
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The LM339 sort of puts out 2 sets of measurements, especially for pin 14. When I first apply all power to the amp, Pin 14 reads about 4.39vDC. The amp draws about 0.7A. The output fets of the RIGHT channel start to get very very warm. I also noticed -23vDC on the left speaker speaker terminals. Then all of a sudden the amp partially shuts itself down and only draws 0.2A idle while pin 14 drops to 0.083vDC.
LM339 on the PS driver board
1: 5.00
2: 5.00
3: 13.86
4: 0.973
5: 3.375
6: 4.53
7: 5.01
8: 3.324
9: 2.951
10: 5.01
11: 8.53
12: 0
13: 5.00
14: 0.083 (Or 4.39)
LM339 on the PS driver board
1: 5.00
2: 5.00
3: 13.86
4: 0.973
5: 3.375
6: 4.53
7: 5.01
8: 3.324
9: 2.951
10: 5.01
11: 8.53
12: 0
13: 5.00
14: 0.083 (Or 4.39)
I'd remove the left channel outputs to see if the amp will power up and the right channel will play. Set the bias fully off for the right channel.
I ended up removing all output BUZ11 FETs as once I removed the left channel ones, I did see -23vDC on the right channel terminals as well.
Whats happening is while pin 14 of theLM339 is high, there is voltage on speaker terminals, but once the voltage drops on Pin 14, the voltage across terminals drops as well. Probably I was just not catching this before as the amp keeps partially shutting down.
Thoughts?
Whats happening is while pin 14 of theLM339 is high, there is voltage on speaker terminals, but once the voltage drops on Pin 14, the voltage across terminals drops as well. Probably I was just not catching this before as the amp keeps partially shutting down.
Thoughts?
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If you connect a load across the speaker terminals, does the amp still have voltage across the terminals?
With all FETs re-installed and the board clamped to the sync, amp was drawing excessively when Left channel was attached to 4-ohm resistive load, and there was -3vDC on that speaker terminal while my external PS was OCP'ing at 3A. Right channel had no voltage on terminals with a 4-ohm resistive load. I then disconnected the resistive load from the left channel, and the amp powered up and idled at 0.6A for awhile. I say awhile because eventually the amp falls to 0.2A idle. No audio on right speaker terminal.
I then removed the left channel fets and still no audio on right speaker terminal under 4-ohm load. Same conditions otherwise.
I then removed the left channel fets and still no audio on right speaker terminal under 4-ohm load. Same conditions otherwise.
I wonder if someone hooked this amp up backward. B+/B- to speaker terminals instead of input power. I bet it was the left channel too. Probably something simple I'm guessing 2 SMD parts.
I had to remove all output FETs as they were getting extremely hot even at 0.7A draw.
I have audio only on pin 1 of the driver board for the left channel, but no audio on any right channel driver board pins. On the left channel, there is a LOT fo square waves on many of the driver board pins whereas not so on the right channel.
On the pre-amp board, I have a deformed negative on the very last pin where the top half is a nice sine wave and the bottom is a half-sliced vertical sine wave.
I have audio only on pin 1 of the driver board for the left channel, but no audio on any right channel driver board pins. On the left channel, there is a LOT fo square waves on many of the driver board pins whereas not so on the right channel.
On the pre-amp board, I have a deformed negative on the very last pin where the top half is a nice sine wave and the bottom is a half-sliced vertical sine wave.
Start with getting the preamp board repaired.
The left sounds like you have noise due to a broken connection the supply voltage and/or ground.
The left sounds like you have noise due to a broken connection the supply voltage and/or ground.
I think the preamp board is actually ok. Good LR audio on all opamps and the gain controls are working. Seems where the audio is exiting the board is where it’s getting clipped and locked down.
I may just start removing smd transistors from the driver boards in this case.
In out of town. Does the dvd have a schematic for this amp? I’ll be back at it in a few days.
I may just start removing smd transistors from the driver boards in this case.
In out of town. Does the dvd have a schematic for this amp? I’ll be back at it in a few days.
See attached.
The output of the last op-amp connects directly to the header pins of the PIM board. If it's clean at the op-amp and not at the header pin, there is a problem on the PIM board.
The output of the last op-amp connects directly to the header pins of the PIM board. If it's clean at the op-amp and not at the header pin, there is a problem on the PIM board.