No problem.
Okay, I have now voltage drop 50/51V in Vcc unregs. R50 measures 1.1V and R20 3.7mV. And I have noticed that turning the pot more drops the voltage drastically and so impossible to have more voltage over R20.
I have measured all the .22 emitter resistors and all are between 1.2 and 1.5mV
Okay, I have now voltage drop 50/51V in Vcc unregs. R50 measures 1.1V and R20 3.7mV. And I have noticed that turning the pot more drops the voltage drastically and so impossible to have more voltage over R20.
I have measured all the .22 emitter resistors and all are between 1.2 and 1.5mV
O.k., the emitters are conducting 6mA each and R20 37mA.
So you are in business again, everything works !!
Now remove the two lamps from the Vcc lines and connect the Vcc's directly to the board.
Now measure R20 again to check it is still ca. 3.7mV.
If so, adjust the pot until you have 27.5mV over R20.
Hans
What are you telling.
Did you try to increase the voltage over R20 with the pot, and 6.5 mV was the max you could get ?
But this was probably still with the lamps in the Vcc lines.
Hans
Actually R20 was 4.3mV and now without lamps 7.3 mV and coming down.
Let me quess, now to idle 27mV? 🙂
Let me quess, now to idle 27mV? 🙂
Question; how do you calculate idle current 275mA from 27.5mV over R20?
Is the idle current through the output transistors from base to emitter?
Is the idle current through the output transistors from base to emitter?
No, idle current flows from collector to emitter.
I did not calculate it, but that's what Mark Levinson specifies.
275mA current through R20 = 0.1 Ohm gives 27.5 mV, that's it.
Do you realise that you have now a 100% working right channel.
Congratulations.
The only thing to be solved is the optocoupler signal.
From point 332 this signal should only go to P210 on the OL-2 board, so try to find out what's wrong with it because OL-2 is disconnected as you said, but nevertheless it generates a signal to the optocoupler input.
Hans
Yes, I realize that it works now. I cannot thank you enough. I am out of words.
Okay, next the opto-coupler.
Okay, next the opto-coupler.
There is still something strange in the amp, but maybe related to the opto problem. I attached the P332 back.
I connected the OL-2 board and temperature sensors from the heatsinks to the mainboard and turned on. Voltage over R20 was considerably higher around 40mV. I waited some time and it started increasing over 50mV. I switched amp off and I think it would have made switch off itself.
How can external "sensor" have this behaviour? I guess OL-2 board is only sensing the areas where it is connected, not tuning anything. Short?
I connected the OL-2 board and temperature sensors from the heatsinks to the mainboard and turned on. Voltage over R20 was considerably higher around 40mV. I waited some time and it started increasing over 50mV. I switched amp off and I think it would have made switch off itself.
How can external "sensor" have this behaviour? I guess OL-2 board is only sensing the areas where it is connected, not tuning anything. Short?
I disconnected the P332 and OL-2 again and tried if it was working again. Same hum(noise) came back like after the output transistor assembly. Sounds like it is coming from the back and center. Could it be transformer hum? at the start DC offset was very high, over the mV meas range of the multimeter. but it came back decent level after a few seconds. After switching off there was still over 100mV DC in the output. Now I will put the lamps back.
Step one:
Bring everything back to where you had 27.8 mV on R20 and ca 15mV on Vout with P332 disconnected and the whole OL-2 board disconnected.
Make sure the voltage over R20 is a stable situation
Step two:
Measure the cable going from optocoupler P332 to OL-2 board P210.
When disconnected on both sides, it should not carry a voltage with the amp switched on and it should have an infinite resistance to Gnd.
Since the amp switched itself off with P332 still connected, there MUST be something wrong with this cable.
Solve this first.
When you can’t find the cause, construct another cable from P332 to P210 to replace the existing cable. Then we can be sure that it is O.K.
Step three:
Unsolder one side of R206 and R212 from the OL-2 board, resulting in blocking the incoming lines P211-1 and P211-5
Then connect the OL-2 board including the (new) line going to the optocoupler from P210 and to the Thermal switches from P211-3
Now measure again the voltage on R20, is it still ca 28mV and stable.
And is Vout still ca 15mV ?
I'll first wait for your findings before we continue.
Hans
O.K. You wrote this at the same time as I was writing.
So you went back already, that's good.
When you compare the output voltage at switch on and switch off with the left channel, how does this compare ?
Hans
I installed the lamps and tried to power on the amp, I noticed that fuse was burned from LEFT channel. Now I need to find fuses. Cannot get it on without the fuse. I remember I bought some but not found yet...
There is no separate fuse for the left or the right channel.
There are two fuses, one in each of the two 220 volt lines.
So one fuse burnt means both amps down.
But it tells that much current was flowing indicating a shortcut somewhere.
Good that you reinserted the lamps and that that the fuses did their job.
Hans
There are even 4 fuses on the primary side before the transformers.
2 * 15 Amp that can be accessed from the outside, but there are also 2 slow blowing fuses inside, type MDL 10 32V, rated at 10Amp/32Volt, shown in your circuit diagram as F300 and F301.
To blow a 15 Amp fuse at 220Volt, means that 3300Watt is consumed !!
That sounds like a very serious short circuit.
So I can understand that you hear some humming.
We have come a long way, so this problem can be solved also.
Hans
2 * 15 Amp that can be accessed from the outside, but there are also 2 slow blowing fuses inside, type MDL 10 32V, rated at 10Amp/32Volt, shown in your circuit diagram as F300 and F301.
To blow a 15 Amp fuse at 220Volt, means that 3300Watt is consumed !!
That sounds like a very serious short circuit.
So I can understand that you hear some humming.
We have come a long way, so this problem can be solved also.
Hans
This amp was using 2 x 8 Amp so I have been using similar ones since(accessed from outside). I found a bag of those and will continue tomorrow. I hope there is only one burned.
And by the way when this amp was still breathing somehow I had strange fuse problem. If I wanted to turn the amp on, I needed to install the power cord just before turning on, otherwise the fuse was burned. (I do not remember any more which channel it was.). Might be helpful info for repairing point of view.
And by the way when this amp was still breathing somehow I had strange fuse problem. If I wanted to turn the amp on, I needed to install the power cord just before turning on, otherwise the fuse was burned. (I do not remember any more which channel it was.). Might be helpful info for repairing point of view.