hello guys here we go again. I'm trying to calibrate the bias currents of a marantz pm 80 bought today at a old market with some outward sign but at a good price.
The service manual show to calibrate Class A to set trimmer to 198mV but coming barely 70 mV in Class A. Mistake some step? should be shorted inputs? I use all 4 points tp? No signal 1khz to test? Thank you
The service manual show to calibrate Class A to set trimmer to 198mV but coming barely 70 mV in Class A. Mistake some step? should be shorted inputs? I use all 4 points tp? No signal 1khz to test? Thank you
Hi!
Had the same problem. In the first instance I settled for 60mv but this was wrong since in around 6 months I got the final transistors burned for one channel. I gave more consideration to this adjustment after the incident.
My thinking:
-a trim voltage to 200mv would mean over 1,1A idle current for each of the transistors in the final stage ( calculated over the 0,18 ohm resistor ). This would also mean a power disipation of 60W for each tranzistor IE 480W power consumption in idle mode....
- I think the Marantz technician made a documentation error in the service manual. A 200mA idle current for class A makes sense (some forums list 150mA as the upper limit after which there is no real win from audio results perspective). This means a trim for 36mV in the stated measurement point (J709-J712).
I highly recommend trimming for 36mV instead of the recommended 198mV.I am happy with this, the unit heats moderately and the audio quality is fine, at least for myself.
Had the same problem. In the first instance I settled for 60mv but this was wrong since in around 6 months I got the final transistors burned for one channel. I gave more consideration to this adjustment after the incident.
My thinking:
-a trim voltage to 200mv would mean over 1,1A idle current for each of the transistors in the final stage ( calculated over the 0,18 ohm resistor ). This would also mean a power disipation of 60W for each tranzistor IE 480W power consumption in idle mode....
- I think the Marantz technician made a documentation error in the service manual. A 200mA idle current for class A makes sense (some forums list 150mA as the upper limit after which there is no real win from audio results perspective). This means a trim for 36mV in the stated measurement point (J709-J712).
I highly recommend trimming for 36mV instead of the recommended 198mV.I am happy with this, the unit heats moderately and the audio quality is fine, at least for myself.
I know this is an old post but it might help someone else.
This is how i read it on the manual and its worked for me.
Its only the pin one on J709 (+) and J712 (-) left side and pin one on J710 (+) and J711 (-) right side that are used the ones marked with a green square.
Turn all four trim pots anti clockwise and connect the meter to pin one on J709 and pin one on J712 turn up R720 till 18mv for 5 mins then press class A button and turn up R762 for 198mV for 5 mins
Repeat on the other channel
When class A is pressed it will already be at about 120mV so only needs to go up about 70mV more
Hope that helps
This is how i read it on the manual and its worked for me.
Its only the pin one on J709 (+) and J712 (-) left side and pin one on J710 (+) and J711 (-) right side that are used the ones marked with a green square.
Turn all four trim pots anti clockwise and connect the meter to pin one on J709 and pin one on J712 turn up R720 till 18mv for 5 mins then press class A button and turn up R762 for 198mV for 5 mins
Repeat on the other channel
When class A is pressed it will already be at about 120mV so only needs to go up about 70mV more
Hope that helps
Hello there!
Please help me configure the Marantz PM80 amplifier correctly.
As I understand it, this amplifier should be hot in A class and moderate hot in AB class. My amp has cold radiators, and only STK is heated. So I decided to check the idle bias current. A
I connect the multimeter to the emitters, for example, Q711 and Q713, and don't get any voltage. If I turn R761 (AB class) to 0, the same situation. I generally do not have a voltage between the exhaust emitters of the transistors. I can’t understand what’s the matter.
Once, I got voltage between the points, adjusted idle bias current for two channels in AB mode. Radiators became warm.
When I switched to mode A - everything is gone, everywhere at zeros in all modes.
The amplifier is working.
I would be grateful for any help.
Thank you in advance!
Please help me configure the Marantz PM80 amplifier correctly.
As I understand it, this amplifier should be hot in A class and moderate hot in AB class. My amp has cold radiators, and only STK is heated. So I decided to check the idle bias current. A
I connect the multimeter to the emitters, for example, Q711 and Q713, and don't get any voltage. If I turn R761 (AB class) to 0, the same situation. I generally do not have a voltage between the exhaust emitters of the transistors. I can’t understand what’s the matter.
Once, I got voltage between the points, adjusted idle bias current for two channels in AB mode. Radiators became warm.
When I switched to mode A - everything is gone, everywhere at zeros in all modes.
The amplifier is working.
I would be grateful for any help.
Thank you in advance!
Did you already checked the voltages in the circuit when switched to Class A? Everythings fine? Anythings missing?