I'm Buying a "Mule" PL400

Found this when I unboxed the amplifier, a true time capsule, completely unmolested. Have you seen a PL like this?
PL400 Transformer.jpg
 
Yeah, didnt see it either...must have been a particularly good batch...
 
PL400 assembled with WOA Control Board and Fully Comp Backplane boards, only bottom row of output transistors installed. No control of the bias voltage on either channel - the bias voltage measured on the Control Board is .014VDC on L and R regardless of the position of the bias controls. I'm using 2N5088 for the Q6 transistors. Using a DBT. Checked for proper voltages from the power supply, good 15 VDC and edge connector voltages on the Control Board, checked for proper bias wiring from the control Board to the backplane boards, and verified the Q6 transistors are inserted correctly in the backplane boards.
What would be some logical troubleshooting steps that I have overlooked?
 
mlucitt said:
PL400 assembled with WOA Control Board and Fully Comp Backplane boards, only bottom row of output transistors installed. No control of the bias voltage on either channel - the bias voltage measured on the Control Board is .014VDC on L and R regardless of the position of the bias controls. I'm using 2N5088 for the Q6 transistors. Using a DBT. Checked for proper voltages from the power supply, good 15 VDC and edge connector voltages on the Control Board, checked for proper bias wiring from the control Board to the backplane boards, and verified the Q6 transistors are inserted correctly in the backplane boards.
What would be some logical troubleshooting steps that I have overlooked?
Click to expand...

MJ21196 closest to transformer, then MJ21195, then MJ21196, then MJ21195 closest to the binding posts?

Missing rail fuses?

It is usually supply voltage related when you have zero bias voltage.
 
Joe, yes the bottom row of output transistors are in the appropriate locations. Rail fuses measure good and + and - 83VDC is in the right places on each channel of the Control Board.
Never had bad bias voltage on both channels before.
 
mlucitt said:
Joe, yes the bottom row of output transistors are in the appropriate locations. Rail fuses measure good and + and - 83VDC is in the right places on each channel of the Control Board.
Never had bad bias voltage on both channels before.
Click to expand...

Control board converted from quasi to full comp?
 
Yes, followed the instructions to convert it. I am using the Control Board that you checked for me a few months back. I know it works...
 
mlucitt said:
Yes, followed the instructions to convert it. I am using the Control Board that you checked for me a few months back. I know it works...
Click to expand...
yup bias dialed right in on the test fixture for both channels if that is the board you are using.

You have +80 on Pad 7L/R and -80 on Pad 3L/R?
 
mlucitt said:
Yes, both the +80 and the -80 are on the Control Board for each channel. DC offsets are .003VDC and .012VDC.
Click to expand...
And the collector to emitter voltage for each of the Q6 bias transistors measured at the Phoenix connector test points is?
 
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