With no outputs populated I see the signal below on pin 2 of U300. I have a nice sine wave on R300 (C355 side). This is only with the gain pot turned up some. Is this correct, signal doesn't change if I remove D311.
One other note, U401 doesn't output anything unless I have a signal being driven in. I assume this is because of the protection circuit.
What should the gate signals look like?
An externally hosted image should be here but it was not working when we last tested it.
One other note, U401 doesn't output anything unless I have a signal being driven in. I assume this is because of the protection circuit.
What should the gate signals look like?
Last edited:
Look for the terminals marked 'carrier' on the schematic diagram. You should see a triangle waveform there. If the other terminal of the same op-amp is near 0v DC, you should see a square wave on the output of the op-amp. If the second terminal of the op-amp isn't near 0v, try shorting the positive speaker terminal to the negative speaker terminal to see if that brings it to near 0v. This is for pin 7 or U301 and U302.
On pin 1 of U300, you should have clean audio. If you don't, you need to follow the signal through toe preamp circuit to see where it becomes distorted.
On pin 1 of U300, you should have clean audio. If you don't, you need to follow the signal through toe preamp circuit to see where it becomes distorted.
The carrier is there, the other pin isn't near zero. I will try shorting the speaker terminals.
The audio fails when it gets to pin 2 of U300, good up to that point. Maybe the opamp is bad. I will lift the input pin.
An externally hosted image should be here but it was not working when we last tested it.
That is pin 5 of U300, is this OK. It's ~7vp-p with 40hz input.
I have the scope set for differential measurement to check the gate signal, since gnd is nonexistent.
That is what I see on the one pair and invert it for the other pair. I only have 4 fets populated right now. All driven from U401. Once gain is increased the power supply starts to hum. Do I need to populate all the outputs at this point or remove what I have placed?
An externally hosted image should be here but it was not working when we last tested it.
That is what I see on the one pair and invert it for the other pair. I only have 4 fets populated right now. All driven from U401. Once gain is increased the power supply starts to hum. Do I need to populate all the outputs at this point or remove what I have placed?
My main concern is the hum from the supply and wondering if the gate signal I'm showing seems OK. I wouldn't expect the supply to hum without a load on the output.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.