开云体育

Re: HP 3455a DVM repair

Harvey White All Messages By This Member #104451 开云体育 If I might: generally, a signal goes through attenuators, then? is converted to digital.? This is done in a floating processing environment called (by HP) the inguard processor.? That is optically coupled to an "outguard" processor, which is the main processor driving the display.? Any break in the chain can result in zeros.? Firstly, I'd take the signal from the inputs, then see how far it gets.? If you can see anything changing in the digitally coupled outputs (optically isolated), might be working.? You'll need to check on both ends of the optical isolators.? That's assuming they have them.? The 3456 has two very isolated transformers that need to be checked.? What I found is that one of the processors itself was dead when I was trying to resurrect some of them. So the bottom line is to try to follow the signal.? An AC signal would be easiest but you'd have to tell it that it's really DC, otherwise you to the AC converter.? If you should try to do an AC signal into the DC input, what you're looking for is the presence or absence of a signal (to a point where the circuitry gets confused and/or ignores it) and after that, the signal isn't there.? At that point, you need to match the AC signal to an AC input, or DC to DC. This is based on my experiences with a 3456, so YMMV Harvey On 4/1/2020 1:36 PM, Bob Albert via groups.io wrote: toggle quoted message Show quoted text Well Chuck, I don't know what to do next with this beast.? It acts as though it works but the display gives nothing useful.? Yet the display electronics seem to be working okay. If I put a signal in, it ignores it.? Open or short on Ohms, voltage or no on volts, gives zeros and no autorange activity.? So perhaps it's an input circuit issue.? In Test I get error 11.? I press test repeatedly and it gives error numbers 10, 9, etc down to 0. The manual sucks.? It tells me to look on module such and such but nowhere does it seem to show me which module is where. Bob On Wednesday, April 1, 2020, 10:22:56 AM PDT, Chuck Harris <cfharris@...> wrote: Hi Bob, I don't see how you can come to that conclusion. The 3455A is highly reparable, and should be well within your abilities.? Lots of people have fixed their own successfully. What you won't be able to do is send its calibration module out for calibration.? You will have to do that yourself.? But, it is not any more difficult to calibrate than the 3456A. It is not my meter of choice, as I greatly prefer the 3456A, but for many, it is a useful addition to their labs. -Chuck Harris Bob Albert via groups.io wrote: >? I don't see a whole lot of encouragement here regarding the possibility of getting my 3455A working.? Maybe I will just put it aside and wait for a scrap unit to swap out boards or parts.? My 3456A still works so I am grateful for that. > Bob >? ? On Wednesday, April 1, 2020, 06:40:17 AM PDT, Chuck Harris <cfharris@...> wrote: > >? The 3455A was a dinosaur when it was first released. > > The 3455A and 3456A were sold side by side, with the > 3455A being about twice as expensive as the much more > capable 3456A.? The 3455A's interesting feature was > it was supposed to be cheap to calibrate.? All you > had to do to do a complete calibration was to unplug > the module in the back panel, and replace it with a > recently calibrated module.? The idea was you could > order up a calibration by mail, and return your old > calibration module as a core... never having to send > the full meter in for calibration. > > Interesting idea, but surely not worth twice the price > of a 3456A. > > I say it was a dinosaur, because it used all small > scale logic rather than large highly capable hybrid > circuitry, like the 3456A.? It should be much easier > to repair, but it should also be much less reliable. > > And, that is my experience with the two units. > > -Chuck Harris > > paul swedberg wrote: >> With respect to the 3455 and 3456 the difference is night and day. I have >> numbers of 3456s and was given a seriously troubled 3455. Quite a >> interesting meter. >> Replaced at least 11 actually malfunctioning chips on the logic board. The >> logics simple so easy to verify the chips were bad. No shot gunning >> involved. Never really did get it working but ended up with a different >> 3455 that needed help and the AC board and it is in fine shape. With >> respect to the old 3455 it has both a logic and voltmeter issue. The 3455 >> uses an unusual processor and teh DVM uses the same proc and a masked eprom >> that is known to go bad. It acts as a state machine. >> The 3456s are losing there eproms and copies can be found on the net. Thank >> heavens. >> Regards >> Paul >> WB8TSL >> >> >> >> > > > > > > > >

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#104451

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