PL400 II Resurrection
- Thread starter TapeHeadOne
- Start date
Hi Peter
Your photo shows -0.67 at the base of Q6R but your earlier note and text above have it as +0.67.
Please check which is correct. If I assume the text is correct, it seems that you have a Q6R B-E short going on some where. Either Q6 itself or a board short of some form. Please check. The other 3 readings look quite normal given this short.
Your photo shows -0.67 at the base of Q6R but your earlier note and text above have it as +0.67.
Please check which is correct. If I assume the text is correct, it seems that you have a Q6R B-E short going on some where. Either Q6 itself or a board short of some form. Please check. The other 3 readings look quite normal given this short.
I swear this thing is haunted. Remember : the left channel was solid at 375 mV, the right was zilch.
I started hunting for solder shorts but found none. What bothered me was the high resistance (250+K) over D13, which I would suspect over a bare diode, but not here. The other side was 12K which is the resistance of R13 before it.
I found R39 (1 Ohm) to be 1.7K, and R37 (22.1 Ohm) at 0.7 M (yes, Meg). I measured the rest, looked OK, and pluged it in.
The Left channel (previously OK) now puts out 0.035V (/10) and the right, previously dead, 20V.
I'm going cuckoo.
Peter
I started hunting for solder shorts but found none. What bothered me was the high resistance (250+K) over D13, which I would suspect over a bare diode, but not here. The other side was 12K which is the resistance of R13 before it.
I found R39 (1 Ohm) to be 1.7K, and R37 (22.1 Ohm) at 0.7 M (yes, Meg). I measured the rest, looked OK, and pluged it in.
The Left channel (previously OK) now puts out 0.035V (/10) and the right, previously dead, 20V.
I'm going cuckoo.
Peter
Yes Gepetto, of course I did. Original resistance and wattage. Even the same brand
Decided to do a quick remeasure :
Previously witn L channel biased 375 mV
1.13/80.5/0.58///-0.7/-0.08/0.08/// 0.67/80/0.66///-1.2/-0.66/-0.66
Now
1.14/79/0.58 ///-0.7/-0.08/-0.08///1.18/80/0.6///-0.7/-0.08/-0.08
EDIT : the biases I'd set to 37.5 mV yesterday are holding
15V+/- is good.
Bias transistor C-E 2V both channels
Decided to do a quick remeasure :
Previously witn L channel biased 375 mV
1.13/80.5/0.58///-0.7/-0.08/0.08/// 0.67/80/0.66///-1.2/-0.66/-0.66
Now
1.14/79/0.58 ///-0.7/-0.08/-0.08///1.18/80/0.6///-0.7/-0.08/-0.08
EDIT : the biases I'd set to 37.5 mV yesterday are holding
15V+/- is good.
Bias transistor C-E 2V both channels
Last edited:
So Peter
You have 2V when measuring at the C-E of the bias transistor but you have 1.84V between the base of Q6L and Q9L on the left channel and 1.88V between the base of Q6R and Q9R on the right channel. Have you confirmed that R21L/R and R30L/R are still 56 ohms? You should be able to dial up the bias to ~2.35V when measured at the bias transistor C-E.
You have 2V when measuring at the C-E of the bias transistor but you have 1.84V between the base of Q6L and Q9L on the left channel and 1.88V between the base of Q6R and Q9R on the right channel. Have you confirmed that R21L/R and R30L/R are still 56 ohms? You should be able to dial up the bias to ~2.35V when measured at the bias transistor C-E.
