Keithley 2700 diode symbol in display - Page 1
Forum section: electronics / testgear

author: petemate
author_rank: Regular Contributor
timestamp: September 29, 2020, 02:57:14 am
content: Hi guys, I noticed that my Keithley 2700 has a "diode symbol" in its display. The symbol is always active, but I don't know what it means as there is no diode-test function in the DMM. Also, no photos online seems to show the diode symbol anywhere and it doesn't seem to be mentioned in the manual. Anyone knows what it means ?

author: bob91343
author_rank: Super Contributor
timestamp: September 29, 2020, 05:37:28 am
content: It's likely that the low Ohms scale is used to test diodes. It would indicate the forward drop.

author: picburner
author_rank: Frequent Contributor
timestamp: September 29, 2020, 06:10:05 am
content: That symbol shouldn't be permanently on.Have you tried doing the display test?The procedure is explained in the service manual.

author: petemate
author_rank: Regular Contributor
timestamp: September 29, 2020, 06:23:44 pm
content: Quote from: picburner on September 29, 2020, 06:10:05 amYes, the symbol turns on and off just fine during the test. Then it remains on when you are back in normal operation.Quote from: bob91343 on September 29, 2020, 05:37:28 amThat doesn't answer the question of why it remains on at all times.

author: picburner
author_rank: Frequent Contributor
timestamp: September 29, 2020, 07:01:51 pm
content: QuoteBased on this we can exclude that the vfd display driver is broken.The problem lies outside the display front panel.

author: coromonadalix
author_rank: Super Contributor
timestamp: September 29, 2020, 07:10:19 pm
content: could be a leaking display driver ic / chip ??

author: floobydust
author_rank: Super Contributor
timestamp: September 29, 2020, 07:24:31 pm
content: Any chance it's the Ohms symbol or OCOMP annunciator? You can program offset compensated ohms shift-OCOMP, or it as Units for math mX+b as ohms symbol.

author: petemate
author_rank: Regular Contributor
timestamp: September 29, 2020, 10:18:57 pm
content: Quote from: coromonadalix on September 29, 2020, 07:10:19 pmIn that case I would expect it to be turning on/off in some odd way along with another symbol when doing the display test. It turns on "correctly", meaning that it turns on when its supposed to in the test sequence.Quote from: floobydust on September 29, 2020, 07:24:31 pmI don't think so. Neither of those are enabled and I also tried a factory reset.Anyway, here's a photo just so that you don't think i'm crazy

author: coromonadalix
author_rank: Super Contributor
timestamp: September 29, 2020, 11:33:13 pm
content: Ask Keithley ??

author: coromonadalix
author_rank: Super Contributor
timestamp: September 30, 2020, 02:17:52 am
content: They do talk about a diode clamp in the digital I/O "db9" connector pin 7 user manual ??https://doc.xdevs.com/docs/Keithley/2700/2701-904-01B.pdfnot the good onehttps://doc.xdevs.com/docs/Keithley/2700

author: petemate
author_rank: Regular Contributor
timestamp: September 30, 2020, 08:35:41 pm
content: Quote from: coromonadalix on September 30, 2020, 02:17:52 amThats for a digital IO port, Doubt that has anything to do with it.

author: floobydust
author_rank: Super Contributor
timestamp: October 02, 2020, 04:23:09 am
content: I would try reset settings to factory defaults, and ensure thefirmwareis the latest. Or maybe it's lonely missing a 7703.The VFD is multiplexed so any driver (or VFD Kovar cold solder joint) issues I would think cause multiple segments or annunciators to get stuck on, such as MON, REAR ~AC etc. over that same digit. That leaves the display controller's RAM having a stuck bit. It's supposed to test that on power-up.

author: exe
author_rank: Unknown
timestamp: October 02, 2020, 02:22:50 pm
content: Is it brighter than the rest?

author: petemate
author_rank: Regular Contributor
timestamp: October 02, 2020, 06:51:21 pm
content: Quote from: floobydust on October 02, 2020, 04:23:09 amI do already have the B09 firmware on display board A02. Anyway, I don't think its a stuck bit because the display test toggles the symbol correctly. So the bit can be changed.Quote from: exe on October 02, 2020, 02:22:50 pmIt does not appear to be.

author: exe
author_rank: Unknown
timestamp: October 02, 2020, 07:08:18 pm
content: Can it be the instrument was repaired and the display board was taken from another keithley instrument (not 2700)?I'd also check settings, I think it's possible to save default power up configuration or something. May be at boot it restores some previously saved state.

author: picburner
author_rank: Frequent Contributor
timestamp: October 02, 2020, 07:10:11 pm
content: Did you update the firmware yourself?Which revision was fitted before, B05?Do you remember if there was this problem previously?

author: petemate
author_rank: Regular Contributor
timestamp: October 02, 2020, 07:26:02 pm
content: Quote from: exe on October 02, 2020, 07:08:18 pmI don't know the history of the device, so it is technically possible. I got it because it was broken, but managed to fix it. The fix didn't involve anything display related, though. A factory reset doesn't answer the question.Quote from: picburner on October 02, 2020, 07:10:11 pmYes, I did the firmware update myself. I do believe it was B06, but I am not sure. I was aware of the issues mentioned in the release notes regarding updating from different versions of the firmware. Don't remember if the symbol was there before the update.

author: floobydust
author_rank: Super Contributor
timestamp: October 04, 2020, 10:08:29 pm
content: Well, I'm out of ideas. I faintly remember something like this happening when I was messing around with the mux boards and didn't have it plugged in properly. I'd ask Keithley support and see if they know.