phase linear 400

[MusicSteve]

So mark the Good one w electrical Tape and you have 2- bad ones?
check the transistor type? (weeks ago,,,,, I thought you mixed them up)
You have a Q-comp board? time to recheck everything.

when adjusting the bias pot , one of them stays at 10mv?

looking at the board I see some spots that look open? (could be the camera flash) I would buss out all solder traces , the point to point traces and push a little on the leads for cracked or not solder joints (that's a funny looking board , solder tracks )
I never had a 400 all mine are II boards

 

[George S.]

Gene, just to move backwards a little to where many people have issues. Storage capacitor polarity. Sometimes it's hard to read on those soldered on circuit boards.
Really look at that little circuit board closely. You most likely have it correct, but please check.
On the upper cap, the wiring connects to +, and the buss bar to -.
On the lower cap, the wiring connects to -, and the bus bar to +.
Many have had this incorrect, please check.

 

[George S.]

Oh, and also check your rail fuses.

 

[gene french]

i lost one side before....changed out the outputs with a documented set of matching 909s
did not change out the drivers....then discovered a bad driver...buddy sent me 2....dont know if they matched or needed to be...
i have retouched 100% of the board at least once...i did find questionable stuff...but, it looks ok now....i checked point to point with dvm in continuity mode....did find a busted trace...but that has all been fixed....i changed out 2 of the drivers and tested with the bottom row looking good...
but after adding the second row....left bias could not be adjusted all the way....ran out of adjustment....moved the drivers left to right...problem followed the drivers...went back to one row again....left side set .... right side dropped to 10mv and thats that....
put all back in original positions...put the two new drivers on right side....from left....and put original drivers back in left side....
disconnected diodes on backplane...all tested ok...checked every resistor on back plane...all ok...powered up...
and this is where i am....both sides set offset to within 2mv of zero...left bias set at 350mv....right bias remains at 10mv....
something is amiss and changing....like i am playing musical chairs with transistors....
on the board...i checked left against right on every resistor....recapped....and undid one side of every diode and checked....
all resistors check good....and equal to the other side....i just dont know...unless the original drivers were damaged....
something is breaking down under load....yesterday early it was all working for maybe 45 minutes then squirreled out....
thanks for looking and helping...this is an old 4 fin....it worked for a month or so until i recapped...and got c8 backwards...i was pushing trying to finish....
has been one thing after another since....the more i fool with these old boards/parts something else crops up....i have one of joes wopls in transit...
and rob sold me a working 8 fin and a parts 4 fin.....they are also in transit...i wanted the 8 fin for joes stuff...but, i think i will order one of joes chassis and get the 8 fin running with these extra parts....i know...long story....sorry....
nothing is simple....lol

 

[gene french]

Oh, and also check your rail fuses.

this is the top....


this is the bottom


rail fuses are good....

 

[gene french]

both sides offset within 2mv of 0
left side bias at 350vm....pot has plenty of adjustment....
right side bias at 10mv...pot dont do squat...
checked diodes and resistors on back plane....
tomorrow scour the board, check diodes resistors and transistors again until the others machines get here....
all of the transistors that i put in / removed / swapped around check ok on the analog vm....
but, this definitely could be something breaking down....
stick a fork in me....i am done....
for today....lol

 

[George S.]

Try bypassing the bias transistors like Joe said. That would eliminate one variable.

 

[MusicSteve]

i lost one side before....changed out the outputs with a documented set of matching 909s
did not change out the drivers....then discovered a bad driver...buddy sent me 2....dont know if they matched or needed to be...
i have retouched 100% of the board at least once...i did find questionable stuff...but, it looks ok now....i checked point to point with dvm in continuity mode....did find a busted trace...but that has all been fixed....i changed out 2 of the drivers and tested with the bottom row looking good...
but after adding the second row....left bias could not be adjusted all the way....ran out of adjustment....moved the drivers left to right...problem followed the drivers...went back to one row again....left side set .... right side dropped to 10mv and thats that....
put all back in original positions...put the two new drivers on right side....from left....and put original drivers back in left side....
disconnected diodes on backplane...all tested ok...checked every resistor on back plane...all ok...powered up...
and this is where i am....both sides set offset to within 2mv of zero...left bias set at 350mv....right bias remains at 10mv....
something is amiss and changing....like i am playing musical chairs with transistors....
on the board...i checked left against right on every resistor....recapped....and undid one side of every diode and checked....
all resistors check good....and equal to the other side....i just dont know...unless the original drivers were damaged....
something is breaking down under load....yesterday early it was all working for maybe 45 minutes then squirreled out....
thanks for looking and helping...this is an old 4 fin....it worked for a month or so until i recapped...and got c8 backwards...i was pushing trying to finish....
has been one thing after another since....the more i fool with these old boards/parts something else crops up....i have one of joes wopls in transit...
and rob sold me a working 8 fin and a parts 4 fin.....they are also in transit...i wanted the 8 fin for joes stuff...but, i think i will order one of joes chassis and get the 8 fin running with these extra parts....i know...long story....sorry....
nothing is simple....lol

Gene
You have to slow down (The problem you have is not clear and ,,,, what transistor )
I'm not a expert w the 400 , Need to start w the basics 1-pic of main caps and mark the + and - 2- Pic of back plane of output transistors , you should have 4 different ones in the first row (bottom)?
You have a Quad-Comp Phase linear 400 (Need a official drawing of the layout of the backplane transistor to double check it)

 

[MusicSteve]

[QUOTE="gene french,
right side bias at 10mv...pot dont do squat... [/QUOTE]
Had is problem , wigged Pot and the Bias changed,, than I chanced Pot (ohm it out and cleaned it before installing it )same problem
this time bais was the same all the time ,, Found open traces to one of the leads going to the Pot ,, Fixed and back running

 

[gene french]

sorry music man....i have adhd in the worst way....
i just sent a pic of the top and bottom power supply capacitors....they are from joe...and upgrade and brand new...and wired as george said how they needed to be installed....the pic is a few posts back...

i have on the bottom row 4 sj2741 transistors....
the rest of the transistors are 909s...but, uninstalled as per georges suggestion until i find the problem with the bias...

 

[gene french]

joe suggested the same....so....i did....

 

[George S.]

Consider removing those anti latch up diodes.

 

[gene french]

Try bypassing the bias transistors like Joe said. That would eliminate one variable.

yes sir....i certainly will....what will this do??
i am not getting dc on either output...
the offset is zero for all practical purposes....both sides
left side bias is perfect and only the right channel bias does not set .... it changed to reading 10mv....period...turning, thumping, nor praying makes any difference...
i did try a few cuss words too...but again....nada....
lol
what will i check when i bypass the bias transistors on the back wall in the little heatsink mount...thats what i been calling them anyway....

 

[MusicSteve]

joe suggested the same....so....i did....

Cap look Good, manual says sj2741 transistors for bottom? or anybody?
so which one are the good? Mark pic

 

[gene french]

Consider removing those anti latch up diodes.

i already did and went back to the 100uf caps as original....
i can reinstall after the diagnostics....if need be

 

[MusicSteve]

yes sir....i certainly will....what will this do??
i am not getting dc on either output...
the offset is zero for all practical purposes....both sides
left side bias is perfect and only the right channel bias does not set .... it changed to reading 10mv....period...turning, thumping, nor praying makes any difference...
i did try a few cuss words too...but again....nada....
lol
what will i check when i bypass the bias transistors on the back wall in the little heatsink mount...thats what i been calling them anyway....

[QUOTE="gene french,
right side bias at 10mv...pot dont do squat... [/QUOTE]

Had this problem , wigged Pot and the Bias changed,, than I chanced Pot (ohm it out and cleaned it before installing it ) same problem
But this time the bias was the same all the time ,, Found open trace to one of the leads going to the Pot ,, Fixed and back running

 

[George S.]

Bias transistor wire or leg broken? Very fragile.

 

[gene french]

Cap look Good, manual says sj2741 transistors for bottom? or anybody?
so which one are the good? Mark pic

they all test good out of circuit....the one that tested bad is in a jar full of bad stuff i have changed out of 3 amps...
the 2741s with the blue dots represent the original transistor in position 3 and 4 counting left to right looking at the back...
the are back on their original side....the two 2471s marked with a blue "j" are the transistors a buddy....named john....sent to me....
only one was bad in position 1 or 2....i would have to go look at the bad transistor to see if it was 1 or position 2....but, i thought it was best to change both on the same channel....i have one spare....that i removed from the same channel as the bad 2471

 

[gene french]

Bias transistor wire or leg broken? Very fragile.

no sir....but, tomorrow i will check again....when i check the board again....

 

[MusicSteve]

Bias transistor wire or leg broken? Very fragile.

And every wire

they all test good out of circuit....the one that tested bad is in a jar full of bad stuff i have changed out of 3 amps...
the 2741s with the blue dots represent the original transistor in position 3 and 4 counting left to right looking at the back...
the are back on their original side....the two 2471s marked with a blue "j" are the transistors a buddy....named john....sent to me....
only one was bad in position 1 or 2....i would have to go look at the bad transistor to see if it was 1 or position 2....but, i thought it was best to change both on the same channel....i have one spare....that i removed from the same channel as the bad 2471

Read my other post ,,,,Bias Pot,,,,,on board
its not a output transistor problem at this point in time