Amp came in with shorted FETs on 1 side of the PS and 1 bank of the output, see 1st pic. I replaced the known defective parts. The amp powers up and has drive signal on both output sides and they match. The issue is the output under load at the speaker terminal.
With a 40hz signal input, and a 1ohm resistive output load, 1 side(negative terminal) looks like it is shifted slightly from the other, see pic 2 set to DC. The 3rd pic is set to AC for a better view. When the signal volume is increased to a higher level, the output begins to distort and starts drawing excessive current, see 4th pic. This level is well before clipping point. I have set the DC offset with the 1 pot to zero at idle but I'm not sure what that 2nd pot is used for. I adjusted it but didn't see any change, it's back to it's original set point. With the amp running at a low volume and no output distortion for several minutes I see no abnormal heat build up using a thermal camera. Any clues?
With a 40hz signal input, and a 1ohm resistive output load, 1 side(negative terminal) looks like it is shifted slightly from the other, see pic 2 set to DC. The 3rd pic is set to AC for a better view. When the signal volume is increased to a higher level, the output begins to distort and starts drawing excessive current, see 4th pic. This level is well before clipping point. I have set the DC offset with the 1 pot to zero at idle but I'm not sure what that 2nd pot is used for. I adjusted it but didn't see any change, it's back to it's original set point. With the amp running at a low volume and no output distortion for several minutes I see no abnormal heat build up using a thermal camera. Any clues?
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One more thing, the 40hz audio output signal, when observed, looks spot on until the amp reaches this "threshold" point in pic4. At this point the amp draws excessive current and it appears half the bridge disappears.
Are you saying that at any level above that in #4 that one of the traces goes flat?
What difference do you see with no load or a 4 ohm load?
Is this a 1 ohm amp? It's not marked as such.
What difference do you see with no load or a 4 ohm load?
Is this a 1 ohm amp? It's not marked as such.
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Something is dropping out causing the output signal to go berserk.
No load or 4ohm has the exact same effect at the same volume level point
Yes this is a 1ohm version amp.
When I monitor each HS/LS bank gates they react the same even at this distortion point, voltage and modulation stay consistent and there is no drop out of drive. The pic here shows the 40hz signal. It is clean up to this point where it starts to distort. One more click and the signal is completely lost and the scope just displays garbage. Turning the volume all the way down will clear and reset the signal output.
No load or 4ohm has the exact same effect at the same volume level point
Yes this is a 1ohm version amp.
When I monitor each HS/LS bank gates they react the same even at this distortion point, voltage and modulation stay consistent and there is no drop out of drive. The pic here shows the 40hz signal. It is clean up to this point where it starts to distort. One more click and the signal is completely lost and the scope just displays garbage. Turning the volume all the way down will clear and reset the signal output.
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It appears that the feedback/servo circuit isn't working. Someone with the diagram for this amp may be able to help. I don't have it.
Typically, the feedback from the two outputs go to a mixer then to an op-amp that drives the op-amp that drives the comparators.
The HD3000 R9 on the following page may give you an idea of the circuit they're using.
Service manual, eprom result list | Elektrotanya
Typically, the feedback from the two outputs go to a mixer then to an op-amp that drives the op-amp that drives the comparators.
The HD3000 R9 on the following page may give you an idea of the circuit they're using.
Service manual, eprom result list | Elektrotanya
Ahh OK. That gives me something to look into, thank you. I'll update when I can resolve this issue.
'drawing excessive current'
this is a large amplifier, how much is it drawing and is your power supply large enough to meet those demands? Is input voltage sagging below 12v?
this is a large amplifier, how much is it drawing and is your power supply large enough to meet those demands? Is input voltage sagging below 12v?
With the black probe to power GND and red probe on the APC pad, amp at idle, no signal no speaker, what is the DC reading of your voltmeter ?