Derek92994's 700 Ser II White Oak conversion

[laatsch55]

Half-biased is no bueno...

 

[MarkWComer]

the only digit u need to worry about is deciding which one to stick up ur backside to stop ur insides from oozing out once you've heard this thing.

HA HA HA! Now that paints a picture!​

 

[FredR]

Half-biased is no bueno...

 

[derek92994]

Had a setup next to the couch, but it was blocking access to some vinyl. Removed some Components and put it on the coffee table with the Thorens.
Recapped the EQ and upgraded 3x OP Amps to 2134PA's. Other than that it was all house cleaning and maintenance today. Back to work tomorrow.
The WOPL G1 board is amazing! So many surprises it throws at me. Thanks to Lee and Joe.

 

[MarkWComer]

Audio porn…. FAP FAP FAP‼️

 

[derek92994]

At work at the moment. Was grumpy last night. Loud pop from right channel amp was powered up for about 3 mins with nothing playing. Hit the power switch and a hot smell come from amp, not like capacitor smell though. Dragged her out of the cabinet and into the naughty corner. Put the pioneer spare back in, sat down, poured a strong one and grumbled I suspect DC protect saved my ass. Damn that was a loud pop.

first steps? Variac? Visual inspection I think. Not much time during the week. Advice greatly appreciated.

 

[Vynuladikt]

First thought with a "loud pop" would be a reversed capacitor, at least the old ones would really go bang, used to do it as a prank. New ones usually just vent smoke and steam, and don't leave shredded electrolyte soaked paper everywhere.

 

[derek92994]

First thought with a "loud pop" would be a reversed capacitor, at least the old ones would really go bang, used to do it as a prank. New ones usually just vent smoke and steam, and don't leave shredded electrolyte soaked paper everywhere.

Its been working for several months, I suspect something on RHS backplane because thats where the smell cane from when the rev D board went. It has a G1 board now. Will get it on the bench this afternoon.

 

[laatsch55]

Check fuses first then visually scan the back planes. Then check for shorted outputs..

 

[derek92994]

Rail fuses etc, all the ones at the back will check. Whats the procedure for checking outputs?

 

[laatsch55]

Positive meter lead on the base, negative on the emitter on the 96's, reverse that for the 95's, in diode mode....any giveaways on the visual, like blown or burnt resistor on the backplanes? Pico fuses good?

 

[derek92994]

Positive meter lead on the base, negative on the emitter on the 96's, reverse that for the 95's, in diode mode....any giveaways on the visual, like blown or burnt resistor on the backplanes? Pico fuses good?

Will update you after work, thanks Lee

 

[derek92994]

Do I use diode mode on multimeter to test outputs and what value does a good/bad one show?

 

[laatsch55]

Yep, .545 or so for good, .000 bad

 

[laatsch55]

And then the Base to collector test.....

 

[laatsch55]

And a shorted output will make all in that row show shorted, then go to ohms to find which one.....

 

[laatsch55]

When you find the offending column, it's easier to pull the outputs and test them individually...

 

[derek92994]

WOPL repair school, the place to be!
Im actually keen to learn more down the track. Will look at purchasing a care package next year.

 

[derek92994]

I have friday off so can spend some time on fault finding. Provided the 2nd Jab doesnt kick my ass

 

[wattsabundant]

Attached is the page from the 400 manual on how to test outputs. It's not in the 700 manual. It works for just about any traditional amp. Read it 2 or 3 times and do what it says and you'll find the shorted device(s). Note that replacement of fuses multiple times does at least $100 worth of damage each time the fuses are replaced. This leads to open emitter resistors etc.

I bought a mili-ohm meter (it reads fractions of an ohm) for $100 on Amazon. It works really good for finding failed outputs as it is far more accurate than a regular DVM at very low resistances. Works great for testing and matching emitter resistors. I don't think it's all that important to match new ones, but you can with the right instrument.