THS720: Difference between revisions
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(attenuator and analog scope section) |
(repair hint) |
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square wave pulser and a DC voltage source. Note that after a cal fail, there | square wave pulser and a DC voltage source. Note that after a cal fail, there | ||
is an error log in a nearby menu indexed by power on count. | is an error log in a nearby menu indexed by power on count. | ||
When confronted by scope calibration failures that say "Cal error, DC balance" | |||
and there are persistant DC offsets that increase with the attenuator settings | |||
try replacing U45 and U46. They are HP CNR201A analog optoisolators, now made | |||
by Avago as the HCNR201-300E. They send a low pass filtered version of the | |||
input signal across the isolation barrier to give the DC levels that can not | |||
cross the high frequency transformer isolation barrier. | |||
The battery pack is, of course, custom. It appears to be 4 C cell NiCd pack | The battery pack is, of course, custom. It appears to be 4 C cell NiCd pack | ||