spund stream rubi 1000d

[timwebb]

im working on this amp and i can only install half of the output transistors. ive replaced the group of transistors on the output driver card that was connected to the output gate. anything im missing?

 

[Perry Babin]

Post a photo of the board.

 

[timwebb]

...

 

[Perry Babin]

What happens if you install all of the output transistors?

 

[timwebb]

it pull more current than my meter can take. i can only install the 3 on the right.

 

[Perry Babin]

Does it draw excessive current immediately or only after the mute delay?

 

[timwebb]

after the delay

 

[Perry Babin]

Before the end of the delay, does the voltage on the positive speaker terminals swing toward the positive rail of the negative rail.

 

[timwebb]

from the negative rail.

 

[timwebb]

3 of the output gate resistors have 11.5v. the three on the left have -47v on the output gate resistor.

 

[Perry Babin]

That would seem to indicate that the problem is with transistors Q124-Q127 or the resistors connected to those transistors. It could also indicate that the board itself is conducting.

 

[timwebb]

where are these two? im over looking them.

 

[Perry Babin]

They are on the driver board. Q124 and Q125 are the MPSA42s that commonly fail.

 

[timwebb]

the MPSA42s on this card are in q35 q36 q40 q41. ive replaced them all due to the legs were discolored from heat. can a resistor be defective if it still read correct?

 

[Perry Babin]

Generally, there are only 2 transistors between the MPSA42s. Are you sure that you have the transistors in the correct locations?

If you shine a bright light from the back of the board, are there any areas between the solder pads that won't pass light?

 

[timwebb]

i changed the two resistors between the MPSA42 transistors and it works now.