MCM-104 was originally tested 9-Jul-99. It failed because the pin 9 (analog power to comparator) 13 ohms to ground.

On 16-Jul-1999 Sangkoo inspected it and wrote "This MCM has short between +5VA_COMP and AGND. Inspection didn't show any suspicious conductive epoxy bridging, even after removing all caps. The resistance at the line did not change at all (about 13.5oms at the bypass caps and about 17.5 ohms at pin 9 and 10)."

On 23-Aug-1999 it was tested again. There was no short. The surface mount components are back on this MCM. Apparently the short was fixed somewhere, somehow. However, the MCM still did not work correctly. Only the first group of 32 channels worked consistently.

All preamp spy channels worked correctly and responded to Vcal normally. The first and 5th chips looked OK on the AMU spy lines. The AMU spy channels one the other 6 chips showed large fluctuations (noise) from one event to the next in most channels.

The discriminator seemed to work.

The Vfb DAC from chip 1 did not appear at TP9 as it should (always 0.00 V), but from the spy channel it is clear that the DAC works -- so there seems to be a connection problem from the TGV chip to the test point.

Conclusion -- there seems to be an AMU-related problem for 7/8 of this MCM, so it must be rejected.