Electronics > Repair

Fluke 8840A Faulty CPU

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coromonadalix:
Wow  im totally impressed by your work  :-+

essele:
Thanks for the compliments! I am feeling quite pleased with myself.

Anyway ... I've reworked the interrupt code and it seems a lot better, all of the buttons are more responsive than they were. I've tested the AC board and that all works perfectly ... which is good, because that's partly where this all started ;-)

I've done some side-by-side testing with a standard Z8 based unit and I can't see any difference.

Just the GPIB board (and hence the serial connectivity) to test now ... I need to get my USB GPIB adapter working on a bit of normal kit first so I know what good looks like. Oh, and I still should probably do something with the reset input.

If anyone feels like donating an 8842 with a faulty CPU , I'd love to get that working as well ... it may just work (with appropriate firmware) but there may be features it uses that I haven't implemented. (Just make sure the screen is ok, I wasted quite a few hours on an 8840 that turned out to have a broken VFD.)

coromonadalix:
If your substitue cpu work,  can you add an serial port instead of the gpib ?? or an usb "rs232" port too ??

Maybe a mix of this project ??
https://www.eevblog.com/forum/projects/ar488-arduino-based-gpib-adapter/

thks


Would be nice to have a 8842 donnor ...

essele:
Hi Coromonadalix,

The CPU communicates with the GPIB card using some kind of serial protocol, so there's no reason I can see why you couldn't develop a different card that provides an external serial or USB port if you wanted to. You would just need to reverse engineer the protocol which I imagine could be done fairly easily by sending individual GPIB commands and then tracking what internal serial comms happens.

You could also hack the firmware to send/receive serial data straight out of the unit, or you could add extra routines in the PSoC to so something similar, but either way that would require a lot more firmware understanding to know where to pull the data from and how to trigger state changes. It's definitely doable, but not something I'm planning on looking at.

The other interesting thing that could be done is to build a completely different interface to the display, this display output code is really easily found in the firmware and could actually be trapped quite simply in the PSoC (it's just writes to the keyboard/display controller) ... so creating something that would drive an LCD for example would be reasonably straightforward. Since I have a machine with a broken VFD I might consider this once I've got everything else working.

coromonadalix:
Hi  essele

You have some 3.2" oled  who where used to convert an hp34401a vfd ...   made by qu1ck

https://www.eevblog.com/forum/repair/hp-34401a-dmm-with-leaking-segments/msg1572961/#msg1572961

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