[volt-nuts] New member with 3457A problem
jerry at hanler.com
Sun Jan 3 21:26:59 EST 2016
I’ve been reading the list for a while, never had a reason to post until now.
I have an HP 3457a, actually two of them, both work great, accurate, stable, etc., except one won’t autocal without an error 512 in auxerr - ohms recharge offset. I’ve had the meters side by side for hours the past few days and can’t seem to locate the problem. There is a difference in the Ohms precharge offset in the failing meter. It looks like a factor mod was performed to lower U216 below +15 by adding resistors to legs 13 and 10. I know there were service notes sent out by HP in 1992 related to the 512 error. the other thing of note is that occasionally when I power on the meter, it will also get a 16 error, which is the offset. I ran diagnostic 4 and calibrated the offset but occasionally the meter will not pass the test no mater how the offset it adjusted. For those of you not familiar, the diagnostic 4 puts the meter in a loop displaying HI or LO depending on the adjustment until the repair tech (me in this case) adjusts the offset correctly. At that point the meter displays ‘Passed’. When the meter fails, usually when cold, the display oscillates between HI/LO like the ADC doesn’t have a connection and the input is floating. I tried swapping U101, the input hybrid, between the two units without luck.
So I am wondering if anyone on the list has run into this problem in the past, and if so, the solution would be appreciated.
By the way, I have a number of voltmeters, can’t seem to get enough, and am pretty good with 3455A repairs having four of them. My black face 3455A is one of my favorites. I also have 2 x 3456A, 2 x 3457A, 3 x 3478a, 2 x 3476, a bunch of Keithely (191, 178, 199, 195, 196, etc) and others, mostly older HP units like the 400. I am currently eyeing a 3458a. I guess I am a volt-nut at heart.
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