Bob,
I have probably repaired 50 or more 3455A¡¯s in the 16 yrs (-5 yrs ago) when I worked for a defense contractor. The original manual was detailed enough and the trouble shooting tree worked quite well. One of the troubleshooting premise was that you had another 3455A¡¯s to trouble shooting with - primarily for inboard vs outboard problem isolation. Be very careful because the ground for the inboard and outboard circuits are different and isolated from each other. The special jumper cable set allowed you to swap the two boards from unit to unit without removing the brds. You would simply watch for the problem to transfer units or not to isolate the failed brd. Then follow the T-shoot tree. Most of the problems I saw were with the fans-the German speed controlled ones-replaced by 12VDC fan (see 11729C fan replace); followed by PS supply issues; the inboard/outboard interconnect cables-the contacts are tinned, not gold plated; calibration issues-usually the high precision resistors under the metal input shield-they are 0.01%;the reed relay on the same input board-sometimes cured by carefully demagnetizing the reed relay; and contamination issues on the input board-required cleaning with soap, water, and brush, then cleaning with 90% IPA and thorough blow dry- the humicoat should have a high gloss with no smudges. Also had 2 problems with the Burr-Brown ADC. Occasional problem with input - somebody tried measuring ohms with +100VDC applied. Other vendors supporting the 3455A had parts units to swap parts and assemblies from, as we also had, but it was simpler to troubleshoot and repair the DMM to component level. The 3455A was a little slower in operation (manual and GPIB operation) than the 3456A. Both units are high quality, high resolution DMM¡¯s. We used the Fluke 5700A to align and cal the HP 3455A.
Don Bitters
