I'm Buying a "Mule" PL400

mlucitt

mlucitt

Veteran and General Yakker
#191
Joined
Jun 24, 2011
Messages
3,367
Location
Jacksonville, FL
#191
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?
 
Gepetto

Gepetto

Administrator
Staff member
#192
Joined
May 15, 2011
Messages
13,535
Location
Sterling, MA
Tagline
Old 'Arn Enthusiast
#192
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.
 
mlucitt

mlucitt

Veteran and General Yakker
#193
Joined
Jun 24, 2011
Messages
3,367
Location
Jacksonville, FL
#193
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.
 
Gepetto

Gepetto

Administrator
Staff member
#194
Joined
May 15, 2011
Messages
13,535
Location
Sterling, MA
Tagline
Old 'Arn Enthusiast
#194
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?
 
Gepetto

Gepetto

Administrator
Staff member
#196
Joined
May 15, 2011
Messages
13,535
Location
Sterling, MA
Tagline
Old 'Arn Enthusiast
#196
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?
 
Gepetto

Gepetto

Administrator
Staff member
#199
Joined
May 15, 2011
Messages
13,535
Location
Sterling, MA
Tagline
Old 'Arn Enthusiast
#199
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?
 
You must log in or register to reply here.
Top