[fixed] Fluke 702 documenting process calibrator - Page 1
Forum section: electronics / repair

author: Bansci
author_rank: Contributor
timestamp: January 29, 2022, 11:53:23 pm
content: Hi all,I bought a broken Fluke 702 documenting process calibrator on ebay as a challenge. I've got the unit powering up, but I've discovered the front end has lost a lot of magic smoke, literally. There's at least two blown inductors, a resistor, and what I think was a dual series diode. Thankfully, the ADC is still functional and it can read DC voltages accuratelyThis means everything totally unobtainium is working at least but it can't source voltage or current or carry out any of the higher functions like resistance sourcing.The amazing xdevs has the service manual here:https://xdevs.com/doc/Fluke/701_702.pdfHowever, the schematics seem to be for a early revision of the 70X. My PCBs are a much later revision. For example the main PCB is Fluke-700-3032 Rev C, but the service manual is Fluke-700-1002The differences are dramatic, I've included a photo of the input board and the corresponding schematic from the service manual. It should just be traces and connectors according to the schematic, but my board has a lot of components...Around the front end the agreement with the schematic is a lot better but still not exact, parts are numbered differently even though its clear they are the same (i.e. the blown input inductors on the source voltage terminal).Does anyone have updated schematics for this system? If not, does anyone have a photo of their main PCB near the input jacks so I can try to tell what is original? If someone has a parts unit I'd also be interested.Any help at all would be very appreciated, thanks. If you want photos of anything let me know. I'm recording the fix and will post it regardless of how far I get.

author: abdulbadii
author_rank: Frequent Contributor
timestamp: January 30, 2022, 02:12:33 am
content: would extract schematic page on PDF or regoogle to ensure there still one can be found from which it's conviniently shown here?

author: Bansci
author_rank: Contributor
timestamp: January 30, 2022, 09:02:41 am
content: I'm not sure what you're suggesting? I've checked Google fairly carefully, tried googling board numbers etc. Also checked the fluke-dmm and Tektronix Google groups.io. Artek manuals also doesn't have anything. Not sure where else to check, if anyone has an idea on another source or photos of a non-destroyed 702 that would really help, thanks

author: Bansci
author_rank: Contributor
timestamp: February 16, 2022, 02:55:37 pm
content: So I finished my repair for now. Managed to get DCV, Ohms, and ACV sourcing working again. DCI source/measure is still broken, mainly through lack of motivation/time.To save you watching the video of the repair below, the unit had vaporised traces due to overvoltage/current at the input jacks, not only did this destroy traces, it also blew resistors, inductors, one current limiting MOSFET and BJT pair, the output op-amp and some clamp diodes. I had to reverse engineer the board a bit due to the schematic differences/missing traces & components, so I've put the KICAD for the frontend amplifier (its different to the 701) as well as the overlaid board images in GIMP I used for figuring out where traces went in a github repo herehttps://github.com/bansci/Fluke702Repair.The current source/measure functionality likely requires a similar level of reverse engineering/debugging which is why I've abandoned it for now. Also, the parts are quite expensive/hard to source these days, Particularly the LTC1510 op amps although equivalents can always be found.Hope this helps someone else some day!