The 1k trimmer can be set to any value that a 330R trimmer can be set.
So that should not be the problem.
But the trimmer must be set for the proper output stage current,
measured as the DC voltage drop across each of the 0.22R resistors.
Check their resistance values (unpowered, in circuit) first.
Some of the 0.22R resistors could be open, or way off in value.
So that should not be the problem.
But the trimmer must be set for the proper output stage current,
measured as the DC voltage drop across each of the 0.22R resistors.
Check their resistance values (unpowered, in circuit) first.
Some of the 0.22R resistors could be open, or way off in value.
Yes…I tried to measure on the r (0,19) also with an 8 ohm load but incredibly I can turn as much as I want and I always measure 0 mV on both channels, I even tried to measure between the output point and the tr emitter always 0. Personally I don't hear distortion but it's strange to me not being able to regulate the current.
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Ok, check each of the 0.22R resistors for proper value of resistance, unpowered in circuit.
Then powered, set the trimmer for a reasonable average of 4.5mV across each.
If you get 0V across the 0.22R resistors, there is a problem upstream.
You'll have to test all the PN junctions in the circuit, then look for bad parts or solder joints.
Are you saying that both channels are the same? Are you sure the DVM is ok?
Try turning the pots the opposite way. Turning CW is not necessarily increase.
Then powered, set the trimmer for a reasonable average of 4.5mV across each.
If you get 0V across the 0.22R resistors, there is a problem upstream.
You'll have to test all the PN junctions in the circuit, then look for bad parts or solder joints.
Are you saying that both channels are the same? Are you sure the DVM is ok?
Try turning the pots the opposite way. Turning CW is not necessarily increase.
yes all transistors are ok, I checked everything I have no problems in fact it also sounds without problems, I thought about the bias when he spoke to me of distortion... they are multi-turn trimmers but I am sure they have done almost all the travel. the absurd thing is that on both channels I have this situation.
Ok, on the schematic, note the DC voltages present at the various circuits nodes and post it here.
If this pcb is capable of functioning as designed, then it could be bad solder joints, broken traces or vias,
a transistor could be installed backwards, etc. But both channels having the same lack of bias current is strange.
If this pcb is capable of functioning as designed, then it could be bad solder joints, broken traces or vias,
a transistor could be installed backwards, etc. But both channels having the same lack of bias current is strange.
after a careful analysis no problem found on the components, I started to do a search on the soldering and some have completely detached, they had used a low quality tin. Restored all the soldering finally I read Bias current set around 5 mV. The only problem is that on the 1943 I have 5 mV, but on the 5200 and both boards, the maximum I find is 1.2 mV with a load of 8 ohm. if I move the trimmer I set 4,5mV also on the 5200 but on 1943 I have almost double. At this point I usually take the highest transistor to set the maximum current but here I have too much difference. Advice for calibration? Thanks
All 0.19/0.20 ohm. Trimmer is ok all run measures perfectly without jumps on both. I need understand which transistor to average the current, these products are unmanageable. the fault was the soldering and in my opinion the customer never noticed and probably already had a channel that sounded bad, another time the other one was damaged too. At the moment it sounds without problems set like this, but in my opinion it's not enough, radiators are cold
I tried both with and without load. These are all tests I'm doing. Anyway, now I set it to 30mA on the highest one so as to have more or less a 20/25 on the other transistors. I can't waste any more time, the mobile should also be reviewed.
the radiator could also handle a higher bias without any problems but I wouldn't want to overdo it
There is no manual, I searched everywhere and the recommended current is unknown. The radiator is wasted with this calibration
Thsbk you For the help
the radiator could also handle a higher bias without any problems but I wouldn't want to overdo it
There is no manual, I searched everywhere and the recommended current is unknown. The radiator is wasted with this calibration
Thsbk you For the help
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the trimmer is only used to regulate the current, I solved the problem by bringing the current above 30mA, but I moved in a different way, I brought the 30mA on the transistor that I measured with the lowest current. Now it starts to sound decent and if I wanted I could push it even further, but I don't know how far I can push it because the final transistors are certainly not original... I repeat that the heatsink could also support a 30W Class A