HP 4395A - Page 222

If the internal test 52 passes, the A33 EXT I/O interface board is probably working. Inspect
cables between the A1 CPU and the A33 EXT I/O interface. If the cable is good, check the
external instrument.
If the internal test 52 fails, replace the A33 EXT I/O interface board.
8-10 Digital Control Troubleshooting