Gibsonian's Cherry Pl 700 Ser I, soon to be a PLWO-1000

[laatsch55]

Top traces --output, bottgpom traces--#1 pic Q4, 2nd--Q5


This is with a new Q5

 

[Gepetto]

Much improved. That technique we used to find this is how you debug backwards in the closed loop until you find the culprit. Q5 was still working but was wounded and was leaking from collector to emitter which caused the rise and fall slew rates to be different. Q4 was trying hard to compensate but could not do it when there was a damaged component in the loop.

 

[laatsch55]

I still have a high bias, and it looks like Q4 is still driving it's nuts off.

 

[laatsch55]

Finally got a clean sine wave-LOADED to 480 watts into 8. Still have to track down the high bias issue, but things are looking up. she gets the listen test soon....

 

[jbeckva]

Finally got a clean sine wave-LOADED to 480 watts into 8. Still have to track down the high bias issue, but things are looking up. she gets the listen test soon....

How low will the bias go now, Lee?

 

[laatsch55]

Just swapped out Q6, wouldn't go below 615, now it starts at 288

 

[jbeckva]

Just swapped out Q6, wouldn't go below 615, now it starts at 288

Better, indeed

 

[laatsch55]

Still have a hi frequency problem above 5K. Pointy top of the sine wave.. Time to strip the 21196's out and go back by pairs. can't find ANYTHING on the board now that's bad. Voltages from channel A to channel B all track within 1-2%. Gotta be the output stage..

 

[jbeckva]

Still have a hi frequency problem above 5K. Pointy top of the sine wave.. Time to strip the 21196's out and go back by pairs. can't find ANYTHING on the board now that's bad. Voltages from channel A to channel B all track within 1-2%. Gotta be the output stage..

Hi Lee. Ok, I'll admit this is probably nuts but it just popped into my head. Is there a way to swap left for right across the WO terminals so that the left side outputs are being driven by the right side of the board and vice versa? That way you'd know in a snap if it's on the board or on the chassis.

Prolly not.. unless the wires had some length to them? (hmm.. idea for a custom "jig" here... )

 

[laatsch55]

I got two things to try first Jer, the aforementioned stripping, and the addition of 2 .33uf 250 volt caps on the output raoils to ground.

 

[laatsch55]

Which didn't do a F^%$#@# bit of good....this is getting frustrating...

 

[Gibsonian]

Wish I could help.

 

[laatsch55]

Wish ya could too Scott. I'll wear it down eventually.

 

[laatsch55]

First of all, thank you Scott for being so patient. This is embarrissing, but here goes. ......................................
C10R and C18R were in the wrong places. C10 was where C18 should have gone and vise versa.

All is well, cept what little pride I had left. Scott I'm gonna shake her down real good this weekend, and she'll be on her way come Monday.

 

[NavLinear]

First of all, thank you Scott for being so patient. This is embarrissing, but here goes. ......................................
C10R and C18R were in the wrong places. C10 was where C18 should have gone and vise versa.

All is well, cept what little pride I had left. Scott I'm gonna shake her down real good this weekend, and she'll be on her way come Monday.

Lee - you're honest and that is one of the things we love about you! Opps happen. No other damage? It's always good to find a fc#k up and correct it.

Listening to Shpongle "Unrealesed Remix". Kinda cool - but different.

 

[Gibsonian]

That's great news Lee. Easy enough too do, that's for sure. Just glad this monkey is off our backs! Thanks for sticking with it.

 

[Gepetto]

Glad you finally nailed the problem Lee, that will definitely affect the slew rate and stability as you found

 

[laatsch55]

Thanks for putting a positive spin on it guys...

 

[laatsch55]

2 months to the day Scott....

 

[Gibsonian]

Thanks for putting a positive spin on it guys...

Easy to do hanging around you Lee. You're one of the most positive people I know. True.