PL400 II Resurrection

I hope the attached file makes it clearer.

Left to Right :

1.13/80.5/0.58///-0.7/-0.08/0.08/// 0.67/80/0.66///-1.2/-0.66/-0.66

Thank you !
 

Attachments

TapeHeadOne said:
I hope the attached file makes it clearer.

Left to Right :

1.13/80.5/0.58///-0.7/-0.08/0.08/// 0.67/80/0.66///-1.2/-0.66/-0.66

Thank you !
Click to expand...

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.
 
The text is correct. 0.67 positive.

Q6R itself measured OK. I'm going to look for a B-E short, I'll start with the soldering, there aren't many candidates for a component short.
 
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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
 
Belay that order, Right channel base wire had come off. I can now bias both channels to 0.0375V , which is a factor 10 short. But the same on both channels.
 
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Hi
Did you change the pin out as earlier post?

“A very good sub for the 3403 is the 2N5088. You will have to transfer the P-strap to the 5088. Pin outs are different.”

If not that check all solder joints again
 
TapeHeadOne said:
Belay that order, Right channel base wire had come off. I can now bias both channels to 0.0375V , which is a factor 10 short. But the same on both channels.
Click to expand...

Very unlikely it is a coincidence. Look for common factors.
 
TapeHeadOne said:
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
Click to expand...

Peter did you repair R39 and R37 and reinstall the original values? They did their job and fused almost open during the thermal event.
 
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
 
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So you are good after finding and replacing the open resistors...
 
Yeah, were it not bias in both channels is a factor 10 too low. Can't get it up, so to speak.
 
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TapeHeadOne said:
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
Click to expand...

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.
 
Peter is being humorous tonight. He cannot get the bias to dial up and he made the joke about other things that can't get up :-)
 
Gepetto said:
Peter is being humorous tonight. He cannot get the bias to dial up and he made the joke about other things that can't get up :)
Click to expand...


No, I meant this part..... Yeah, we're it not bias in both channels is a factor 10 too low I got the "Get it up" part.
 
Peter can only get it to 37.5mV instead of 375mV. Both channels are now stable but bias is low by a factor of 10.

He needs one of Navo's sexy nurse babes to fix this.
 
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