!!! ANYONE SEE THE PROBLEM HERE ???? PL700 Series 2

[Greg]

Picked this one up from Audio shop they couldn't fix ....... can you spot the problem ??

 

[AngrySailor]

Series II is full comp?

 

[Gepetto]

Series II is full comp?

Very few series 2 amps were produced as full comp Andrew. Most were quasi comp

 

[Greg]

Every Transistor NPN .....?

 

[Gepetto]

Every Transistor NPN .....?

If the amp is quasi comp, every device will be an NPN transistor on the back wall.

 

[Greg]

Ahhhhh !! I will Send some more pics to Validate !! Interesting ...Everyday I learn something new lol ! very cool !!

 

[Greg]

Just when I think I know everything You guys remind me I dont lol ...... So this would be a Quasi ! ??
See pics and battle scars !!

 

[Greg]

More Pics Joe I think I need More parts !!! lol

 

[George S.]

It's a quasi. WOPL it.

 

[mr_rye89]

Ahhh there’s the kaboom…….

 

[J!m]

That board is medium-well. I prefer them rare.

 

[Greg]

Hmmmmm Question .. ok so back to the drawing board then for me lol OK So To make it a FULL COMP ( Half Risesitors NPN orther half PNP ) I have noted that compared to my Last FULL COMP WOPL project I can see the following Differences so Far ( see attached pic ( red circled )
1. On my past full Comp It did NOT have the diodes as I have circled on this back plane they were just Straight JUMPERS
2. Also Noted One channel Does not have the Green Caps ( 334k ) missing on one channel never a sign they were ever installed lol !! ??

Would there be any other changes to BACK PLANE to accomidate a FULL COMP are the Diodes basically JUMPED out on The WOPL Build as a full comp anyways ??


Thanks in advance !!

Greg

 

[Greg]

This picture was of a what would be a " FULL COMP " back plane I had done a WOPL upgrade to I kept the orginal Backplane and all worked out quite well !!! You can see the differences ( Diodes verses straight Jumper ? ) The missing Caps Might be a a Random ? ( see attached pic )

 

[AngrySailor]

Compare the schematics, there’s quite a few differences. I don’t have them on my phone, only hard copies at home as I’ll be converting my 700/1 to full comp with factory backplanes using the WO driver board (have to convert from quasi build to full comp build also).

 

[WOPL Sniffer]

I see the problem................. It hasn't been Full WOPL'd yet............

 

[Gepetto]

The channel with the toasted zoebel resistors has been ultrasonically oscillating. There is no reason for a zoebel to overheat except for oscillating channel or a failed (shorted) coupling capacitor.

The oscillating is not an uncommon problem with stock PL amps.

You can see by the cap tacked on the back side of the control board on one channel that someone was attempting to tame that oscillation.

 

[Greg]

Hello Gents !! So in comparing last amp I did WOPL and the QUASI ( my first Quasi ) I had noticed my first Amp ( COMP ) did not have D107 or D108 installed ? ( see attached ) I see the diodes are present on my Quasi but never were on the COMP ? !!?? All seemed to work fine with out ? What might be the function of these diodes Quais compsred to Full Comp ? Thx in advance !!

 

[Gepetto]

Hello Gents !! So in comparing last amp I did WOPL and the QUASI ( my first Quasi ) I had noticed my first Amp ( COMP ) did not have D107 or D108 installed ? ( see attached ) I see the diodes are present on my Quasi but never were on the COMP ? !!?? All seemed to work fine with out ? What might be the function of these diodes Quais compsred to Full Comp ? Thx in advance !! View attachment 76356 View attachment 76357
View attachment 76356 View attachment 76357

They are flyback diodes and should be on all amps, quasi and full comp. The latter days of PL, they looked to cut costs everywhere they could.

These diodes must have made the chopping block. They are absolutely on the White Oak Audio backplanes.

 

[Gepetto]

And they are not the reason this amp has a problem...

 

[Greg]

Sent you email to order back plane !