Need advice on Marantz scope diagnosis
30 Apr 2006 11:48:49 -0700
I'm trying to diagnois a non-working scope on a Marantz 150.
Does any one know what the service manual means when they say to "short
the collectors on both FET's " in order to center the beam to see if
the vertical or horizontal amp is bad.
There is a pair for each amp.(H905 & H906 and H907 & H908)
I know that FET's don't have a collector but they are labeled that way
on the board and schematic so that's not the question.
The question is: Do I connect the two collectors together to short them
or do I connect them to ground to short them? I was going to connect
them together but a "tech" thought I should connect them to ground.
To each other, I should think.
Also, to test if both amps are out, can I short both pairs at once?
Hopefully it won't come to that, so the first question is more
More than one person responding would be good.
Without seeing the schematic it is hard to say, but from the sound of
things you have a balanced, long tail pair amplifier. That being the
case, you would equalised the drive on the two sides of the tube by
shorting the collectors to each other, not to ground.