phase linear 400

No...you are not passing DC to the speaker posts, start with the small signal transistors first. If q5 , q7 or q10 were the problem there would be a healthy dose of DC on the outs.m
 
Carefully measure the C-E voltage on Q6, the bias transistor. Your right channel is the problem one so max out the pot on that channel. Compare it to the left channel C-E voltage on Q6 when properly set to the correct bias voltage.

Be careful.

Low bias voltage will do no harm Gene. It is too high a bias voltage that you must worry about.
 
thank you....i had to give up on that pl14 (no designation a or b) board....i changed q4 and got bias....on the right channel....left channel was functioning....bias set at 350....
the transistor checked good with both meters and the little chinese transistor checker i got....after removal and replacement....
i kept swapping transistors and it got worst the more i fiddled with the board....there is something evil afoot....lol
i had a 14b i got from mr. george....i robbed q8 and q9, but replaced them a while back....had it as a spare board....
swapped the board after a preliminary check of diodes and transistors....it checked out....as best that i can do....no shorts or opens....
the dbt was bright and dimmed as it normally would...
and....now....
it has left and right bias....both adjustable....it has no dc on left channel....
when you first power it on....it shows a few volts dc on right channel....but not rail voltage......
if you just sit there and wait....leaving the unit on the dbt live....the voltage bleeds off all the way down to .001....same as the functioning side....
at this time the dcp board engages if i place the output wires into j2....
after power off....and waiting a few minutes....the dc reappears....waiting while powered up....again you can watch the offset drop to .001....
the bias on the right channel is 417 with the dbt engaged....
the bias on the left channel is 485 with the dbt engaged....
i dont leave it on but a minute or two....
strange....but true....

i will go measure q6....but, i did at one time on the previous board change out those transistors as i have bought a few spares....nothing changed....
i will now however go and check c to e on q6....however, i no longer have a normal bias voltage on either side...
 
c to e on left side....2.24 v dc
c to e on right side 2.17 v dc...
with dbt engaged and full line current...

this board is not recapped....i do have one cap that could lose a bit of weight....but not morbidly obese....
thanks for helping me ....
 
Gene, guy I got that board/amp from said it worked and was using it for a electric guitar amp. I never plugged it in before gutting it.
That PL300 S2 I recently purchased was also doing the "little bit of DC, but it's dropping". I attributed it to caps as guy said it had been sitting unused for several decades. Not plugging it back in until it's recapped.
Time to rebuild those old boards with all new parts and low noise metal film resistors. That's what the 300 will get.
 
George S. said:
Gene, guy I got that board/amp from said it worked and was using it for a electric guitar amp. I never plugged it in before gutting it.
That PL300 S2 I recently purchased was also doing the "little bit of DC, but it's dropping". I attributed it to caps as guy said it had been sitting unused for several decades. Not plugging it back in until it's recapped.
Time to rebuild those old boards with all new parts and low noise metal film resistors. That's what the 300 will get.[/QUOTE
great idea....thanks !!!!
Click to expand...
 
gene french said:
thank you....i had to give up on that pl14 (no designation a or b) board....i changed q4 and got bias....on the right channel....left channel was functioning....bias set at 350....
the transistor checked good with both meters and the little chinese transistor checker i got....after removal and replacement....
i kept swapping transistors and it got worst the more i fiddled with the board....there is something evil afoot....lol
i had a 14b i got from mr. george....i robbed q8 and q9, but replaced them a while back....had it as a spare board....
swapped the board after a preliminary check of diodes and transistors....it checked out....as best that i can do....no shorts or opens....
the dbt was bright and dimmed as it normally would...
and....now....
it has left and right bias....both adjustable....it has no dc on left channel....
when you first power it on....it shows a few volts dc on right channel....but not rail voltage......
if you just sit there and wait....leaving the unit on the dbt live....the voltage bleeds off all the way down to .001....same as the functioning side....
at this time the dcp board engages if i place the output wires into j2....
after power off....and waiting a few minutes....the dc reappears....waiting while powered up....again you can watch the offset drop to .001....
the bias on the right channel is 417 with the dbt engaged....
the bias on the left channel is 485 with the dbt engaged....
i dont leave it on but a minute or two....
strange....but true....

i will go measure q6....but, i did at one time on the previous board change out those transistors as i have bought a few spares....nothing changed....
i will now however go and check c to e on q6....however, i no longer have a normal bias voltage on either side...
Click to expand...
Gotta love a man of few words … :-)
 
not much progress today...have the 14b recapped...
everything checks out...when i populate bottom row of outputs....i can not put outputs in row 1 or 2 together...the dbtester does not glow bright...but does not dim...bottom row colomn 1 3 4..ok...
row 2 3 4 ok...but you cant put outputs in row 1 and 2...really strange this machine....i have blown no fuses ...no damaged outputs...etc...the dcprotect works as expected except when populating column 1 and 2 in bottom row...tomorrow...
 
a few more words....if i may....or if i may not....
progress....but still a bit lost
populated the outputs....no brite lites...and it dims as expected...
changed the rectifier...changed column 2 socket...changed all 150 ohm resistors in the bottom row...they were way off...
now is more consistent....
left channel offset.... .009
right channel offset... .002
right bias set at 350 and is adjustable as one would expect...
left bias minimum at 450 and is adjustable but only higher...that is as low as it goes...
the only way to get consistent results....is to by pass the dbtester....
if you engage it...sometimes it wont trigger the relay in the dcp board...sometimes it will...
it plays music...
got to be something else breaking down on the board...
will continue tomorrow...
tried to make it short....but, to be honest...i did not try really hard....
 
Hmm, something is out of spec on the problem channel. It may well come down to the voltages Joe asked you to check on the bias transistor.
 
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