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Author Topic: HP419A Oscillations  (Read 1656 times)

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Offline gridleak

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HP419A Oscillations
« on: January 05, 2022, 06:20:45 am »
Back in April 2020 I reported my 419 had a strange oscillation of 2vpp at 9hz occurring at at 3-- cardinal ranges (e.g. 3mv,30mv...30v,300v). Having no success in troubleshooting, ( I had spent days checking resistors and connections on switch S1) even with the kind help of experts, I put that meter aside, and paid attention to a second 419 I have. I re-lamped, and built a new battery pack for the second meter. The second meter doesn't have the strange oscillation.  I swapped A4 boards  to verify the oscillation remained with the first meter. The oscillations must be due to some defect in one or more photocells in meter one, or in one or more of the components surrounding the chopper block. Ripping out, and replacing the diodes and caps on the chopper block would have been a PITA with no guarantee of success, if it turns out to be a photocell.  Getting the second meter working was preferable. I know that I have seen this oscillation complaint on other forums, as well. So, hopefully, this report should be useful for those with an oscillating 419.

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