Keithley 616 electrometer rescue - Page 1
Forum section: electronics / repair

author: vindoline
author_rank: Unknown
timestamp: May 25, 2025, 05:14:30 pm
content: A while back my beloved Keithley 616 electrometer stopped working. Upon powering up, only the left-most LED was displayed.After a quick, initial, inspection showed that the voltages on the power rails seemed OK, I consulted the schematics and theory of operation section in the manual. It turns out that only part of the LED display is multiplexed and that is the part that is not working in my unit. The manual reveals that the multiplexing circuitry, as well as the AtoD converter, are located on a custom ‘LSI’chip. Oh no!All hope was not lost though. While going over past repair threads on the forum I found a post from a member, Joel_S, who had had the same problem:https://www.eevblog.com/forum/testgear/keithley-616-teardown/msg2971854/#msg2971854He was able to locate the patent that Keithley had filed on this chip and reverse-engineer a modern replacement board. This is the sort of acomplishment that I find almost magical as a non-EE!I reached out to Joel and he was able to put together a complete DIY kit for me, including a pre-programmed micro.I spent a very relaxing Sunday morning soldering up the board and installing it in my 616.It works again! I can get back to exploring femptoamps!Much thanks and a big shout-out to Joel. I don’t think his post got the attention it deserved – probably because he posted at the end of a years old teardown post.

author: coppercone2
author_rank: Super Contributor
timestamp: May 25, 2025, 05:26:43 pm
content: I got rid of mine in perhaps anger (repeated trolling) but things like people making new cards gives me confidence in possibly trying the design again, the resistance spec is impressive but I hatttttttttteeeeeeeeeeeeeeeee the manual rangingThere needs to be a repository of Keithley 616 substitutes and replacements. And the best thing would be a full list of exactly which parts are difficult to obtain so they can get 'solved' slowly. It makes me feel like I am buying a fairly simple thing but the parts are all threaded in fantoms / mile non standardALso what the hell do they do to the PCBs in there. It has like a coating around the parts. It looks like wax. It made me not want to even try to work on those parts (cleaning).I am really not kidding for some reason I really dislike how its built and the design. It scares me on some psychological subconscious level.and when i see things likeOperational amplifier : manufacture pN : SPECIALi almost just bought a new one but I looked at the tear down picture and came to my senses. maybe someone else has the stomach for it

author: Joel_S
author_rank: Contributor
timestamp: May 25, 2025, 06:54:16 pm
content: Hi John,Thanks for the kind feedback ! I'm really happy to hear that your K616 is back in operation. I would just hate to hear that such a nice instrument got scrapped because of a failed unobtanium part. My guess is that your electrometer is now ready for 40 years of good service.And, by the way : your failure analysis was 100% correct, the fault was in the LSI chip. Murphy's Law had struck once again, but we defeated it !Thanks again for your post,Joel

author: vindoline
author_rank: Unknown
timestamp: May 25, 2025, 09:25:13 pm
content: The only bit that was a bit odd is that there was no way to use the mounting stand-off you designed into the board. My digital board does not have a hole there - there is a (germanium!) transistor there. Everything fits though, and it seems very secure. Hopefully it will be good for the next generation!

author: Joel_S
author_rank: Contributor
timestamp: May 26, 2025, 07:58:30 pm
content: Well, obviously the hole which is on my Keithley logic PC board does not exist in other versions of it. From the IC date codes on your board, it looks like it has been built in 1974, which is quite early in the commercial lifespan of the 616.If you believe more mechanical support is needed for the module, maybe you'd have to explore other solutions. I have no idea about what kind of solution could be designed, I would never even think of drilling the Keithley board.Joel