MCM-168 was tested 20-Oct-99. It is rated a "grade B" MCM because it has 4 bad channels (not 4 bad chips). These channels are 46, 49, 170, 173.

The 4 channels are called bad because they have almost no response to changes in Vcal. Actually, they do show a very small response -- a change of about 25 ADC channels for a change in Vcal from 3.48 to 4.7. This is about 1/10 the change seen in a "normal" channel. Two of these channels (49, 173) show no reponse on the preamp spy channel -- suggesting a broken connection between the preamp and the AMU/ADC or else bad preamp channels. The other two have normal signals on the preamp spy lines. In one of the two cases (170), the AMU MUX shows a slightly smaller than normal response, but not as small as the response seen in the ADCs.

This MCM also has some channels (75, 79, 89, 136, 139, 143, 146) with responses which are slightly smaller than normal -- around 2/3 of the response normally seen. That is, the change in ADC values is around 150 channels for Vcal = 4.71 --> 3.48, while 250 or so is the normal change. This should not be a significant problem, but this is the first MCM on which I have seen this type of gain variation within a single AMU/ADC chip, so it is surprising. Out of this group of channels 75, 79, 89 just seem to have lower gain than normal. Channels 136, 139, 143, 146 also seem to have slightly lower gain, but in addition they have slightly higher pedestals and are a little noisier.