Re: FG 504 Offset problem

Tom Miller <tmiller@...>

Do you have the +/- 25 volts? What is on pin 2 of the amp? Can you set that to 0 volts
with R1140? The +7 at pin 6 sounds bad if pin 2 is near 0 volts. What about Q1160
and 1180. Are they ok? Check R1160 and 1180.

----- Original Message -----
From: gehp01
Sent: Saturday, August 28, 2010 5:16 PM
Subject: [TekScopes] FG 504 Offset problem


Dear All,
The positive side of the DC offset of my FG-504 is not working, but negative is working fine.
I thought this would be an easy fix, but I am about to quit.
In case someone gets interested, I have uploaded this section of the schematics.
First, I checked the + and - 15V and the +/- 4V input and they are ok.
Next, I pulled out Q-1150 and Q-1170 and, to my surprize, both are ok also.
With these transistors out of circuit, the output of U-1145 goes from
-13V to + 7.0V.
I ran out of ideas.
I would not venture to replace U1145 since this would mean to disassemble almost the entire unit.
Any suggestions?
Thank you

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