R&E » Keithley 2001 repair

VRIN is buffered by U517 and tied to BUFF. The signal at BUFF is routed through R233,
K503, K500, the input protection circuit and Q513 to the input buffer (Q512 and U520).
The buffered signal is tied to AMP IN.

The signal at AMP IN is then routed to the variable gain ampliÞer (VGA) and, being
positive, follows the non-inverting x1 path that consists of R530, Q509, Q507, U519,
R531, U509, Q501, and U516 to pin 15 of the TRMS converter U517.

The output of the U517 is routed to the multiplexer U511 through R219. The output
(OUT) of the multiplexer is routed through buffer U342 to ACV/A. The signal at ACV/
A is routed through U320 (/AC pulled low) and applied to the A/D buffer (U322),
which is conÞgured for x1 gain. Measure the output at A/D IN.