Richard, Jim, Dave:

we removed the 6th ADC from h1seih23 after it was consistently showing a 4000 count offset in its channel-13 (14th channel). The entire ADC-ribbon-interfacecard were replaced with off the shelf spares which fixed h1seih23.

We installed the suspect ADC-ribbon-interface on the DTS x1seih23 front end as the 3rd ADC (ADC2) on Friday afternoon (3rd April). We restarted the front end several times that afternoon, but did not see any offset in any ADC channel. We left this running over the weekend.

This morning the ADC channels still looked good. I restarted the IOP model 5 times, no problems were observered. I started a series of power down tests, and found that the IOP model would not run (with very large irig-b errors) if I powered down the IO Chassis, using the front panel switch, for only 5 seconds. If I powered the IO Chassis down for 1 minutes (either switch only or switch and DC power cord disconnect) the IOP would start correctly.

I then performed the power cycle test 5 times, no re-occurance of ADC offsets were observed.

Bottom line, we dont know why this ADC's ch13 went into a 4k offset mode at 12:30am Friday. We cannot reproduce the error.