phase linear 400

[gene french]

well, my theory fell through....illogical....and nowhere near fascinating....
when i disconnect the b+ red wire from the control board...but leaving in the fuse to allow b+ to the backplane....
no dc on the output....
it has to be on the board....i just aint looked hard enough yet....

Thought. There may additional "legacy" wiring in there from when it was wired for 220 VAC. Maybe that's why it was blown up. Compare it to a working amp.

yes sir....but tomorrow...
i am done for today....
thank you for helping....

 

[gene french]

Hmm. I promptly gutted all my amps before WOPLing them, so I'm no further help.
If it were me, I'd open up a working similar amp(you have a bunch) that has the same control board and configure the problem amp to match.
Don't let that export transformer throw you. As long as B+ and B- rail voltages are correct, your good with that wiring. Working, later!

voltages are good....before and after the rectifier....
i dont think its related to the transformer....
tomorrow is another sunrise....
i will get it....
lol

 

[George S.]

Yup, never rush it.

 

[gene french]

i got spares!!!
lololol

 

[gene french]

well...disconnected the pl14 again....compared right to left...have 2 14as and 1 14b .....compared board to board...i did find d4 shorted....yesterday d5 was shorted...hard to believe i would not have caught d4 at the same time...i think there is a bunch of cripple parts on that board....i will rest a bit...and go over the board again...now i wish i had a variac....lol

 

[George S.]

Less amps, more variacs.

 

[gene french]

dont you have a spare???
lolololol
i really should order one...
can you recommend a good one to buy used on ebay....
that may not be so chinese....

 

[George S.]

Get the one Sniff has for sale. Send him a PM.

 

[George S.]

Here you go Gene, it's a nice one. Sniff knows his Variacs.
https://forums.phxaudiotape.com/thr...on-the-auction-block-100-plus-shipping.10910/

 

[gene french]

well...no more dc on the outputs....on this dual voltage 400 ..learned a bunch on this one....
found more shorted diodes...how did i keep missing them.....it aint that difficult....every time i reexamined the board...i found another...i even found one on the right channel....
need to repopulate left channel and set bias....
i will not put this one in service for a bit...will let it burn...as this wounded soldier syndrome may not be over....it is wired back into dcp and board activates....thank god i did not have to pay me by the hour...lol
but for me...very satisfying to figure it out...
learn and rekindle vintage stuff....

 

[gene french]

delima....starting to repopulate....drivers are 66546...one is bad....dont have another...
i can...
1. replace 66546 with 410 (one channel or both)
2. replace 66546 with 2741...(one channel or
both)
3. put 66546 in row 2 and 4...use f pl909 in column 1 and 3...since outputs are f pl909s...
what makes the most sense....kinda leaning to option 3....will use fewer resources....

 

[gene french]

delima....starting to repopulate....drivers are 66546...one is bad....dont have another...
i can...
1. replace 66546 with 410 (one channel or both)
2. replace 66546 with 2741...(one channel or
both)
3. put 66546 in row 2 and 4...use f pl909 in column 1 and 3...since outputs are f pl909s...
what makes the most sense....kinda leaning to option 3....will use fewer resources....

 

[laatsch55]

A 66546 is a 410...

 

[gene french]

gotcha...

 

[gene french]

this board has me stumped...nothing shows bad...yet very low bias voltage on right channel...
left bias set...it does play....right side not up to par....
fascinating....open to suggestions....

 

[George S.]

I'm thinking probably a bad transistor. Your low voltage testors won't find it. Read up on testing power transistors.

 

[AngrySailor]

this board has me stumped...nothing shows bad...yet very low bias voltage on right channel...
left bias set...it does play....right side not up to par....
fascinating....open to suggestions....

Haven’t had time to read the whole thread but you got all WOPL stuff in this right? I nuked Linda doing something stupid a while back and couldn’t find my low bias issue anywhere in the driver board. Was resistors on the back plane. Think r7&8 or 9&10??? (by memory so..) anyways the 1 ohm wang dangers as well as bias resistors were toast along with all the emitter resistors... turned out I had the bird repaired but still had issues in the backplane.

 

[George S.]

Gene is resurrecting cheap original amps from the dead. I'm glad he enjoys doing so, I wouldn't.
Don has commented several times about doing the "Output Load Sharing" test that's in the service manual. This might give him some insight if it's a back wall issue as Andrew has experienced.

 

[laatsch55]

A transistor can pass the diode junction tests and still have no gain.
Now that you have a good channel, reference ground with the negative lead and starting with Q1, compare every leg of every transistor.
Check emitter resistors and bias resistors first..

 

[gene french]

A transistor can pass the diode junction tests and still have no gain.
Now that you have a good channel, reference ground with the negative lead and starting with Q1, compare every leg of every transistor.
Check emitter resistors and bias resistors first..

i think this is whats happening...i checked every component on the back plane including resistors....and tested every junction on rhe control board and diodes and resistors...i have all transistors....i guess time to swap out a few....leaning toward q8 and q9 to start with...
i do enjoy doing this...i learn a lot...thanks for suggestions...i also have a spare 400 with a pl14 board...i can always compare too...