Whoreo's (Rob's) WOPL 400 in for Warranty Work

[laatsch55]

Finally got the Dr. to lift my 10lb restriction. So we can fix Rob's blown WOPL. Of course the shipping goons had their way with it...

 

[laatsch55]

It was blowing rail fuses....

 

[laatsch55]

1----21196 and 1---21195 on the left channel were shorted...

 

[laatsch55]

It appears the right channel is intact.

Q7, Q10 on the left are still good. The pico fuses on the backplanes are good. This is also the amp where one of the backplane locators came loose during shipment to Canada. Therefore, the backplanes will be liberated and brought off the chassis and be inspected to make sure no washers are bouncing around between the backplane and the chassis.

 

[laatsch55]

Left side backplanes lifted and all outputs tested( 2-bad), right side backplanes lifted and inspected for rogue washer (none found), outputs tested-all good...

 

[laatsch55]

Going back together...

 

[laatsch55]

All new outputs in the side with the 2 blown ones....just cause...

 

[laatsch55]

There is a trick to putting in the outputs. A strong magnet and a long T-handle allen wrench........and at times a lot of patience.
When building a WOPL, before I install the backplanes I will test set the outputs and put them in order on a card so the outputs are matched to the socket. Due to the small tolerances in the solderable sockets , each output can have a slightly different lead pattern, so a test fit can relieve a lot of stress when you are ready to install outputs...

 

[laatsch55]

Outputs in...

 

[laatsch55]

Passed theDBT and variac power up...setting bias and checkinh offset...

 

[laatsch55]

Got a good relay click...

 

[laatsch55]

Offset----Left 16mv, Right 18mv....Bias 380...

 

[laatsch55]

On the horns it goes...

 

[laatsch55]

Aw jeez....what a fucked up sounding amplifier!! WHEW!!~!

 

[laatsch55]

Got some funny bias readings, Left channel NPN row---318mv, PNP row 438, Right channel NPN Row---385, PNP Row---256...

 

[Billboard]

I always enjoy the repair threads, thanks for taking the time to post Lee.

 

[laatsch55]

Welcome bud....a lot more to write up on this one. I have checked all resistors, semiconductors etc in circuit and nothing APPEARS wrong, but it sounds like total shit. Low voltage power supply is good, main PSU is good. I have not isolated the protection circuit yet, but the 1304, 05 pairs check good in circuit......

Interesting ......

 

[laatsch55]

100 hz, 136 mv input. Both channels driven....

Definitely have some problems....IIRC, this looks like when I had wounded Q7's or Q5's a few years ago...

What do ya think Joe??

 

[laatsch55]

With just channel A driven in the first pic , with just channel b driven in the 2nd...

 

[laatsch55]

Both channels driven at 10k hz. 136mv input

Looks pretty much the same at 20khz...