400 Series II (standard) repair

[FredR]

Got it. Thanks.

 

[laatsch55]

We aim to please Fred...the Phoenix way....

 

[mlucitt]

This was the condition of my R39 10 Ohm resistor. Split from bow to stern.

 

[FredR]

What on earth did that?

This was the condition of my R39 10 Ohm resistor. Split from bow to stern.
View attachment 34878

 

[laatsch55]

Shorted output usually...

 

[laatsch55]

Besides being tired...

 

[mlucitt]

That's the way I found it, and the amp smelled like stale beer. Notice the original PL wire cover on the resistor lead, it was hard and brittle. Pretty obvious heat damage all at once, or over a long period of time.

 

[WOPL Sniffer]

That's the way I found it, and the amp smelled like stale beer. Notice the original PL wire cover on the resistor lead, it was hard and brittle. Pretty obvious heat damage all at once, or over a long period of time.

Stale beer? Hmmmm, I don't recall owning a 400 but in the old days you never know.... Any roaches hidden in there? Then I know it might have been mine...

 

[mlucitt]

It was a 700B that was totally dead... I assumed it spent a sad life as a stage amp at Gilley's Bar in Pasadena, Texas.

 

[laatsch55]

I can think of a lot worse ways to go other than staff at Gilley's...

 

[rinman77]

None. For each channel you have two - one on each rail.

View attachment 34876

I have a schematic for the PL400 series 1 & series 2, but neither of them look like the one you show here. In my series 1 schematic the bottom row transistors are labeled Q12, Q14, Q16 and Q18, (left to right). In my series 2 schematic they are labeled Q108, Q109, Q112 and Q113. So how many different schematics are there for the same unit?
Ron

 

[mlucitt]

The PL400 I Service Manual shows three different schematics. One each for Control Boards PL400C, PL14A, and PL14B. The PL400C schematic shows drivers as Q9 and Q13 (one channel), and the PL14A/B schematic shows drivers as Q11 and Q12 (one channel).

 

[rinman77]

The PL400 I Service Manual shows three different schematics. One each for Control Boards PL400C, PL14A, and PL14B. The PL400C schematic shows drivers as Q9 and Q13 (one channel), and the PL14A/B schematic shows drivers as Q11 and Q12 (one channel).

OK, thanks for the clarification.
Here's another question: Can anybody tell me what the circled components are in the photo below? I think I figured out the rest of what I'm seeing.
Thanks!

 

[Gepetto]

Ferrite beads to tame high frequency parasitic oscillation

They are not shown on schematics

 

[rinman77]

Thanks! I would not have been able to figure that one out.

 

[wattsabundant]

The 700B service manual mentions them in a bulletin that discusses oscillations.