Hi, I wonder if people can help with  a question about a HP3458A. The unit is an old one, the serial number is 00227, the firmware EPROMS were version 4, and the NVRAM chips have datecode 88 (that makes them 34 years old, amazing they are still going!). The unit is quite clean inside, although it had been dropped on the front panel as the terminal post fixing has broken, as have some of the lugs that hold the PCB to the front panel. It appears to have last been for cal in 2012 as it's got an Agilent electrical safety check sticker of that date. It reads within 10-20uV of another (Keysight Calibrated) 3458A on the 10V range. So far, I've ordered a replacement front panel from Keysight, reflashed the EPROMs to rev 8, and have read the NVRAMs and ordered replacements and sockets. It's also on day 3 of a CAL72 drift test to see how stable it is (according to the rear panel it has the Opt002 reference). However, this morning I noticed an error after an ACAL, "ERR 204 HARDWARE FAILURE - FLATNESS DAC CONVERGENCE 195". I gather this is an issue in the A2 board, any clues of what to look for? Thanks!

			Attila Kinali

On Tue, 5 Jul 2022 08:22:02 +0100 Keith <keith@peardrop.co.uk> wrote: > So far, I've ordered a replacement front panel from Keysight, reflashed the EPROMs to > rev 8, and have read the NVRAMs and ordered replacements and sockets. It's also on day 3 of > a CAL72 drift test to see how stable it is (according to the rear panel it has the Opt002 > reference). Cal72 can take quite some time to stabilize if your 3458 has been off for a few years. E.g. mine has not been powered for at least a decade, probably two and it took Cal72 half a year to stabilize (see attached graph) > However, this morning I noticed an error after an ACAL, "ERR 204 HARDWARE FAILURE - FLATNESS DAC CONVERGENCE 195". I gather this is an issue in the A2 board, any clues of what to look for? Uh.. this sounds like you have a defect component on your ADC board. I would start poking around the integrator (U110,U111,U112) and see if the voltages look like they should. Then check the output of the comparator (U142), whether it matches what it should do. Attila Kinali -- In science if you know what you are doing you should not be doing it. In engineering if you do not know what you are doing you should not be doing it. -- Richard W. Hamming, The Art of Doing Science and Engineering