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

[Gepetto]

Is the bias setting in range?

 

[laatsch55]

Yes, ranges from 225 to 560.

 

[Gepetto]

All seems good Lee on that front. Both channels adjustable?

 

[laatsch55]

Yes, they respond wewll. No abnomal heating until I remove the minus drive fuses then Q5 heats up quickly.

 

[laatsch55]

Pretty cagey tonight Joe. So on the White Oak board with as much power that is dropped over the TIP-31c that can cause my bulb to stay bright?? Ah sooooo.

 

[laatsch55]

Okay, ran out to the One-ton and grabbed the Fluke Cl;ampmeter. We are only drawing.(point) 6 amps.

 

[Gepetto]

Hi Lee
You are drawing 0.6A with no load on the amp? Or do you mean 0.06A? Have you compared that to your other amp? If 0.6A is true that is apporx 72W and you would be developing a bunch of heat somewhere that you would notice.

 

[laatsch55]

Well , just so happens the last move on the bias pots was full and after a few seconds without the DBT in line all 4 bias resistors went up. They have been replaced and I just got home. Wll see if I still have a problem in a few minutes. Yes Joe, .6 amps. After taking the DBT out amps went to 2.6, and before I could shut it down the bias resistors went.

 

[Gepetto]

Lee are the 2N3403s in this amp toast? High bias like that would result. You should check that out.

 

[laatsch55]

Besiders the 4-Bias resistors, these other components died, Q11L, Q11R, Q12L, Q12R, Q10L, Q10R, D9L, D9R, Q8L, Q8R, Q5L, Q5R. Replaced the following components besides the one listed above-- D10L, D10R, D13L, D13R, Q9L, Q9R, Flyback diodes on terminal strips. I believe the order of failure was Q8 on both channels died valiantly trying to protect the rest from the 110 volt square wave, but lost the battle. Q15R was not far behind, K1 in the protect relay went and the rest went after I did not find Q8 bad and took it off the DBT and then things got bad. Q7, then Q10, Q11, D9, and finallyQ12.................I think it went this way.

 

[laatsch55]

the good news is it powers on and behaves. Will test later tonight. I'm tired.

 

[Gepetto]

Glad you slayed the dragon Lee. Good work. Was this the original control board you were debugging?

I was under the impression you were debugging the second board you built?

 

[laatsch55]

No , Joe , This was the second board. I don't think the first is going to be near as bad.. I t still amazes me just how many components can be in a failure cascade, and then be exponentially compounded by by the wrong diagnosis and debug.

 

[laatsch55]

Left channel good, high bias on the right now. The 3403 checks ok on the DMM and B& K trans tester, but with the crude tests that they are can this 3403 be suffering from "no gain" and not work??

 

[Gepetto]

Are the output devices all installed at this point Lee or just the predrivers?

 

[Gepetto]

You could be suffering from low gain on that channel 3403, that would cause excessive bias. Does it adjust at all? Or barely?

 

[laatsch55]

Jusst barely Joe and then it seems backwards to the left channel, as in i have to turn it the opposite way of the left to get the small drop I do get, and won't go lower than .685

 

[laatsch55]

Just the pre-drivers--15024's
s and 1 set of outputs per rail.

 

[laatsch55]

My daddy was a Gibson..... My momma was a Fender.............That's why they call me mindbender.......... Back to work on Cathy-" Mindbender" Amp.

 

[Gibsonian]

that's funny Lee - my handle for gmail instant messaging is Dr. Mindbender! And I'm half Gibson, but no Fender in my heritage that I know of.