Fluke 5100b / 5101b old service manual - Page 1
Forum section: electronics / repair

author: asp
author_rank: Regular Contributor
timestamp: November 04, 2021, 11:47:43 am
content: HiI am trying to repair my Fluke 5101B unit that does not display anything. I got it with lots of issues and thus far I managed to fix the PSU and now I have all the voltages but after fixing the PSU there is nothing shown on the display. I look for a manual for the unit but I think this is a old version of the unit and the CPU board does not look at all like the one in the service manual. Mine is a 2 boards clamped together and I would like to know if somebody can help me with a old version of the manual (specifically the CPU ASSY schematic and part numbers) and maybe firmware.My board does not even have the test points indicated on the manuals available online.I can also post some pictures if somebody is interested.Thanks

author: Runco990
author_rank: Frequent Contributor
timestamp: November 04, 2021, 09:53:58 pm
content: I have an old 5100A (same machine) that had no display. I chased the CPU and everything else. You'd THINK the clock for the display comes from the CPU cards, but you'd be WRONG!!!In the end it turns out there is another clock.... a 555 timer ic nicely hidden in the bottom right corner of the power supply regulator board. You might want to test that signal.... I put in a socket and a new 555. BOOM! DISPLAY!!!You can pull out ALL the other cards and boot with only the power supply, front board, and rear boards for CPU. You should get a display, although errors. But it should light up.It only took me a months to stumble on this and I HAVE the paper manual!Crazy design.

author: bdunham7
author_rank: Super Contributor
timestamp: November 04, 2021, 10:27:11 pm
content: Does the display flicker or is it just blank? Certainly check out the issueRunco990mentioned, especially if it is totally blank. And as he said, you can pull all of the full-height modules and just leave the short boards in the back and the front panel and ranging assembly in place (the PSU won't work with the ranging unit out). This should boot up and give you an Error 6 display.I have two manuals for this, one is the earlier one you are looking for. I also have the firmware, unfortunately it is packaged for the later model units that have a single-board CPU assembly. The size of EEPROMs got larger as time went on and they were able to consolidate the CPU assembly. I don't know if you could figure out how to distribute that onto the larger number of smaller EEPROMS, but if you do please let me know! I had one with a failed CPU assembly that I concluded was likely a failed or corrupt EEPROM, but that ended up being a parts unit. It was the old double-board version like yours. The problem was the display not working and just showing the briefest flash every once in a while.Here's a link to the older Fluke 5101B manual:http://ftb.ko4bb.com/getsimple/index.php?id=download&file=Fluke/Fluke_5100B_522987.pdfHere's the firmware (with no guarantees--I have not tried it myself!!!)

author: asp
author_rank: Regular Contributor
timestamp: November 05, 2021, 04:59:36 am
content: HiThanks for the hints. I have already repaired the PSU board but I did not check the 555IC, but I presume it is working and I will tell you in a sec whyWhat I have seen with my CPU board is that sometimes (just sometimes) it does try to start and there is the bottom left segment of the second "0" in the output section that does flicker about once a second. If I split the boards and remove the “PROM - RAM - ROM” card, (so inserting just the CPU board alone) all the bottom parts of the segments light up and flicker and with some leds lighting up as well. Because of this I think the 555 is working and I do get a clock, otherwise I think the display would be blank.I want to start changing logic chips on the boards and schematics will help here (thanks for the old manual). If changing logic chips and memory chips does not work I will print a PCB using the available schematic (new version) and make a DIY CPU ASSY, unless anyone around here has a spare CPU board at a reasonable price?

author: asp
author_rank: Regular Contributor
timestamp: November 09, 2021, 01:12:46 pm
content: So my issue now is that CPU RESET line is kept high. I will check U2, U34, U35 and U36 which seem to be the ones responsible for RST (the CPU is good because I tested the CPU in another equipment that uses the same CPU) and the NE555 generates a clock at around 56Hz (the manual states it should be 60). I will post my findings after I will replace the ICs and retest the boardI cannot find anywhere a fluke 500x controller board or a fluke 850x controller board (they seem to share the same board across the calibrator and DMM). It's the firmware that is different and some jumpers on the board itself.

author: bdunham7
author_rank: Super Contributor
timestamp: November 09, 2021, 02:38:39 pm
content: Quote from: asp on November 09, 2021, 01:12:46 pmI believe that the RESET line is inverted, so it goes low for a reset and should be high otherwise. Check that and make sure before you do too much troubleshooting!I recall that the DMM controllers are not interchangeable, although they are similar. I can't remember why.

author: picburner
author_rank: Frequent Contributor
timestamp: November 09, 2021, 06:24:36 pm
content: I can assure you that the IEEE-488 Interface module 384057, taken from a dmm, also works on the 5100B calibrator.I made this test with a positive result (.....if that's what you meant by "controller").

author: bdunham7
author_rank: Super Contributor
timestamp: November 09, 2021, 06:32:02 pm
content: Quote from: picburner on November 09, 2021, 06:24:36 pmWe're referring to the CPU module, not the GPIB board. Obviously the firmware will be different, but also the amount of firmware will be different. I'd have to drag some out and look to try and remember what the issue was that prevented me from swapping them.

author: asp
author_rank: Regular Contributor
timestamp: November 10, 2021, 07:29:18 pm
content: Ok. So back to square one now. I got it to flicker again and we ware both right. You are right that RST needs to be high but I was also right as the CPU RESET circuit was faulty. Now I am back to square 1, but with some news.Does anyone think the attached images look odd for an 74LS10? Pins 1,14,6 and 4 (in that order)?Later Edit:The signals look like that with no PROM board attached and with socketed memory removed. PIN1 looks really close to what the signals on the data lines look with memory attached. I think it's U2 the one that is generating this issues since PIN4 is the output of U2 (and U2 should be a simple hex inverter). I will change it tomorrow and will recheck.

author: asp
author_rank: Regular Contributor
timestamp: November 13, 2021, 02:22:45 pm
content: So I got it working or at least partially. One of the 74LS04 was bad (it was generating weird signals) and now I suspect that 74LS10 is also bad. The board boots now randomly and when it does, it goes into flicker mode after like 10 seconds.When it boots it displays the version (1.0.5) on the AC screen and than it displays +0.0000 on the DC part (but it kind of flickers and the buttons do that as well) and after like 10 seconds it starts to display some weird signs and the cpu resets itself. I will change 74LS10 and come back. If it's not 74LS10 it may either be SRAM or the one of the PROMs, but I will update this thread when I have more information.LATER EDIT:If you have issues with the CPU board be sure to check all your signals. Everything should either be square or sine nothing in between (and no sawtooth wave signals either. I will try later on to download the firmware and post it here if I can get it. Oh..my clock generation on the actual board does not look like the schematic. Below you can see a board with what id different. Marked in red are actual differences. Yellow are tested and are the same

author: asp
author_rank: Regular Contributor
timestamp: November 23, 2021, 09:19:45 am
content: Would anyone need firmware 1.0.5 for 5101 B ? (it's the old (double board) format). I managed to get the firmware from the PROMs. The PROMs are Intel 2716 compatible

author: alm
author_rank: Super Contributor
timestamp: November 23, 2021, 02:25:57 pm
content: Could you upload the firmware tohttp://www.ko4bb.com/getsimple/index.php?id=upload-instructionsandhttps://xdevs.com/contact/?

author: asp
author_rank: Regular Contributor
timestamp: November 25, 2021, 12:57:06 pm
content: I have uploaded the ROMs to both sites. And will add a zip file here as wellCan anyone please tell me if I leave just the CPU Assy, the Tape Board (needed to power the CPU Assy), the PSU and the front panel connected, should the front panel respond to button presses or not? Mine does not and would want to know if it is an issue with one of the above boards. If I connect all the needed boards I sometimes get an Err 1 which is something related to invalid key sequence and the front panel does not respond to key presses

author: bdunham7
author_rank: Super Contributor
timestamp: November 25, 2021, 02:44:41 pm
content: If you leave all of the full-height modules out except the ranging board, you should get an Error 6. I don't know if it will respond to any button presses. I don't know if it matters, but are you leaving the isolator board in?

author: asp
author_rank: Regular Contributor
timestamp: November 25, 2021, 05:54:09 pm
content: To answer my own question: Yes, the front panel should work without any of the full-height modules (including the ranging board). One if the issues my device had was a 4503 IC on the front panel display being badand the other issue a P2111 memory being bad as well.Now I am back at fixing the device which seems to have lots of shortened caps. I think I have changed half of them thus farBTW: Does anyone know of a good 74/40/45 database logic IC database? I have written my own tester for SRAM,logic IC's and EEPROM Reader based but I would need a logic input/output database for it (I have testedhttps://raw.githubusercontent.com/akshaybaweja/Smart-IC-Tester/master/database.txtbut it seems to be lacking lots of functionality and some IC's like 4520 are not defined correctly)

author: asp
author_rank: Regular Contributor
timestamp: December 20, 2021, 02:21:32 pm
content: Quote from: bdunham7 on November 04, 2021, 10:27:11 pmAre you willing to part with your failed CPU assembly? I am willing to spend some bucks on it if you want to sell it. I would need one as mine is a complete bummer. It used to work but it died and I have changed every single component on the board so I think it's a short somewhere on the 2nd layer.

author: bdunham7
author_rank: Super Contributor
timestamp: December 20, 2021, 04:37:33 pm
content: Quote from: asp on December 20, 2021, 02:21:32 pmI'm going to have to dig for it! Give me some time, perhaps after the holidays I can resolve to doing a bit of cleanup and reorg and then maybe it will show up.

author: asp
author_rank: Regular Contributor
timestamp: December 29, 2021, 08:57:26 pm
content: As an update, the board has started after a reheat under the 8080 so I think it's a short somewhere in layer 2 (out of 3 layers). I did redo all the VIAs with solder and for now it seems to work but I won't keep my hopes up that this is a long time repair.Also there was a short in the TID122 between pin 14 and 5 and I budged a 1N4148 on the back of the front panel board since a new tid122 is around 25$ (and that does not make any sense). But the partially working TID122 is now socketed so in case I do come across a good one in the future I can easily swap it.Also I did change all the IC's on the CPU board that are 74LS with 74HC since they are faster (the only exception there is the 74LS51 for which I could not find the HC version).What I want to do is change all the LEDs on the front panel with new ones as some of them are dimAlso it seems that my cpu board is more or less the same board that is in a Fluke 8502

author: madao
author_rank: Frequent Contributor
timestamp: January 05, 2022, 03:09:26 pm
content: *removed*

author: m k
author_rank: Super Contributor
timestamp: January 05, 2022, 04:30:59 pm
content: https://www.ebay.ca/itm/261157255157

author: mircado
author_rank: Newbie
timestamp: September 26, 2025, 11:25:52 am
content: HelloI have the same unit but it gives me error messagesError6I checked the power supply board and i found two short diodes but i don't know their values it seem strange they are connected to the input of the regulator 7925

author: coromonadalix
author_rank: Super Contributor
timestamp: September 26, 2025, 12:47:39 pm
content: 78xx 79xx series of regulators are normally in the 1 amp range try to find some 1N4005 1N4006 1N4007 diodes rated 1 amp or 3 amps onesbut when you find damaged part(s) always refer to their pcb location ex: cr10 cr25 ... it help others