HP6632B Overvoltage problem [SOLVED]

[xtof]

Problem: 2 HP 6632B showing same error: overvoltage error when setting Vout to around 8V. Rest seems OK.

Overvoltage is detected at U306, comparing Vout+ with a combination of Vprog (from the microcontroller) and DMON_COMP. Vprog comes directly from the uC board, measured OK. So the problem is DMON_COMP being to low. DMON_COMP comes from U313, in a buffer amp configuration with input IMON_H IMON_L and Vout-. On the 6632B IMON_H/L are not connected, so it is just Vout- that is buffered, probably to prevent floating of the Vout- versus Vprog reference. Vout- at the input was measured at 0V (pin3) OK, but U313 output is -13V, so the Opamp U313 is broken. Spares ordered from Ebay at around 5USD, and replaced. Problem solved.

Christophe

[bitseeker]

Welcome to the forum, Christophe. That was quite the all-encompassing post. Thanks for sharing and following up with the solution.