Fluke 8000A DMM – Line Power / Battery Operation Modification Possible? - Page 1
Forum section: electronics / testgear

author: Vonsgarage
author_rank: Contributor
timestamp: July 24, 2025, 11:35:54 am
content: [ Specified attachment is not available ]Good day;I have checked information on this Fluke 8000A DMM on this website and have noted there are occasional references to modifying it as follows:1. Eliminate the NiCad batteries completely and convert to line power only2. Convert the NiCad batteries to a more current chemistry (Li-Ion) and modify the charging circuit as needed.If anyone has performed either of these modifications, would they be so kind as to share what they did? I’m handy with a soldering iron but not too sharp otherwise.My unit has the NiCad option. I understand they need to remain in circuit for the device to operate. The #53 lamp is still glowing away. Just use this fellow on the bench and am starting to worry about those old batteries.I whipped up a schematic that shows both the AC powered model and the Battery powered model (-01) on one drawing. Perhaps this could assist in some way?

author: Grandchuck
author_rank: Super Contributor
timestamp: July 24, 2025, 12:30:48 pm
content: Can you edit your picture size?

author: Kleinstein
author_rank: Super Contributor
timestamp: July 24, 2025, 07:22:30 pm
content: Really resize the picture. With a normal screen it is way too large.The way easier path would be converting to AC only. Without looking at the schematics the simply way would be to replace the battery pack with a suitable voltage and power zener diode. An alternative is a TL431 with transistor to make an adjustable voltage clamp.The other option would be convert to the circuit for the AC only version - if the transformer allows.

author: edavid
author_rank: Super Contributor
timestamp: July 24, 2025, 08:54:11 pm
content: Quote from: Kleinstein on July 24, 2025, 07:22:30 pmThat is certainly true, but a workaround is to use the browser "Open Image in New Tab" function to scale it.QuoteI don't recommend this, because a shunt regulator generates too much heat in the sealed case. It's much better to use a series regulator. I recently did this with an "MP1584" step-down module from China. I added a 1000uF capacitor on the input and a 33uF capacitor on the output, but the values are not critical. The output voltage should be about 5V, but can be adjusted for minimum squeal from the 8000A DC-DC converter transformer.Another issue is that the input transformer is always connected to line power. To fix this, you can cut a trace on the top of the circuit board and wire the 2 sides to an unused set of terminals on the power switch. (See second and third photos below. The second photo shows a previous attempt with an LM317 regulator - not recommended because of heat - so ignore that - the switch wiring is the same.) Obviously this is optional.

author: floobydust
author_rank: Super Contributor
timestamp: July 24, 2025, 09:32:35 pm
content: I think your MP1584 solution is missing the filter cap C19. What about C17, C18? Unless the manual is a totally different board rev, the pics show them. I'm confused.Your LM317 solution needs a heatsink and what input voltage do you get for it? It's enough?I'm surprised the 5V digital rail is not IC regulated in the 8000A.The battery is a shunt-regulator, and filter capacitor, and a power source when there is no mains. I wouldn't run the DMM without a battery, it keeps the 5V rail from going up. I think 7V is the max. for TTL.Different power transformer T1 for the 8000A-01 battery option. Manual mentions measuring 5.6VAC but that's over 7VDC or maybe the lamp helps that.Fluke 345637 for -01 battery option, rated 18.6V 1.2A and 115/230VAC primary. But today we are seeing 120VAC mains.Fluke 345629 rated 16V or maybe 18.6VCT 1.2A and 5VAC and 115/230VAC primary for the base models.I would add a filter capacitor with an LDO or 7805 not depending what voltage the transformer puts out. My preference is not a buck converter because they are electrically noisy.The non-battery version uses 4,000uF 10V for C19. I can't find what uses the "+5V unregulated" node, it might be just a test point.https://www.eevblog.com/forum/testgear/fluke-8000a-dmm-schematicBAMA Fluke 8000A manual

author: edavid
author_rank: Super Contributor
timestamp: July 24, 2025, 09:44:19 pm
content: Quote from: floobydust on July 24, 2025, 09:32:35 pmThat's the 1000uF cap that I mentioned. It's mounted on the MP1584 PCB.QuoteI left the original DC-DC converter and C17/C18 in place.QuoteA heatsink would be a good idea, but I gave up on the linear regulator idea. I think the input voltage was about 11V.QuoteI didn't see any effect on the meter readings. I don't think the MP1584 board is any noisier than the existing DC-DC converter.

author: floobydust
author_rank: Super Contributor
timestamp: July 24, 2025, 10:00:45 pm
content: Thanks for the pics. I did not see the cap.I remember when these first came out, way ahead of their time- almost outer space. Everyone was in awe but I think they were expensive $299 in 1972 is $2,300 today.

author: coppercone2
author_rank: Super Contributor
timestamp: July 24, 2025, 10:04:01 pm
content: I recommend this mod for the meter. Take out the batteries and then run it over with a carIIRC mine worked (before I did the above modification), IIRC I just randomly decided to put capacitors in stead of the battery. I thought well, its kinda similar. My first meter and it almost got me to dump electronics as a hobbyI liked the other thread we had about this meter recently where people had similar opinions to mine about the meter.I wonder how many sad employees there was in 1978 when the non technical guy made them use it instead of a actual good DMM.Actually I think it just worked without the caps too. Is something bad supposed to happen if you run the meter without batteries?Something clued me in that electronics might not be so bad at the same time. Maybe I found some HP power supply in the trash or something, and actually had a pleasant repair experience.

author: floobydust
author_rank: Super Contributor
timestamp: July 24, 2025, 10:15:32 pm
content: Your love is a bit confusing - run over "it" you mean the batteries? "it almost got me to dump electronics" ? I don't get it.In the 70's most DMM's had a kooky rechargeable battery scheme. So much NiCd.With no batteries I think the 5V rail will go high. Hard to tell how the transformer does with today's high line 120VAC vs 115VAC.Over 7V? I think it will stress the IC's.

author: edavid
author_rank: Super Contributor
timestamp: July 24, 2025, 10:24:56 pm
content: Quote from: floobydust on July 24, 2025, 10:15:32 pmWith no batteries the meter won't work, but it (probably) won't be damaged.

author: J-R
author_rank: Super Contributor
timestamp: July 25, 2025, 02:05:38 am
content: Ugh, the 8000A is really basic! 1999 counts, very limited functions. The oddball mA sec option brings the tiniest amount of interest. Why tinker so much with it unless you're going to restore its original functionality? That is typically more attractive to everyone than chopping things up.Tenergy has NiCd cells with tabs for sale on eBay. AA is a bit small and could get overheated by the charging circuit, D is a bit spendy, but maybe the Sub C (2200mAh) could work ($2.50/ea)? Don't use NiMH.A while back when I went looking for an 8000A to add to my "collection" I chose Lo Ohms with no battery. It wasn't working when I got it, but the only thing it needed was cleaning the selector switches.

author: edavid
author_rank: Super Contributor
timestamp: July 25, 2025, 02:54:29 am
content: Quote from: J-R on July 25, 2025, 02:05:38 am1. It's a lot cheaper to stick an MP1584 board in there ($0.50 or less) than to spend $10+ on batteries.2. The primitive charging circuit will cook a set of NiCd cells in a year or so, and then you have toxic waste to dispose of (and you may have to clean NiCd gunk out of the meter). The mod is a permanent fix and doesn't create a disposal problem.

author: AVGresponding
author_rank: Super Contributor
timestamp: July 25, 2025, 05:18:43 am
content: MED5763 has already posted a linear reg mod for these on this forum, probably in the TEA thread. I'm getting ready for work so I don't have time to search for it now.

author: coppercone2
author_rank: Super Contributor
timestamp: July 25, 2025, 08:15:15 am
content: are you sure it won't work with some capacitors? I think I got mine to work with something really basicI cut the leaked cells out, and must have wired in something really basic, I recall capacitors instead of the cells, and it worked.I know I cut the capacitors out at some point, but I don't remember if I tried to replace it with solder tab batteries. Perhaps there is a revision that works with the cells cut out? But it has been many years. I am almost sure I just had capacitors there.I still have the capacitors that were soldered in there (I had to solder a wire to it) in my junk box (I cut the caps out before I threw the meter out). Somehow it worked, but I think I later just decided to buy NICAD cells to solder in there. And then later I got super pissed at the ranging buttons and threw it out.At most I could have soldered a load resistor in there or something. It was definitely no more then passives or maybe a diode. This was before I started experimenting with IC

author: robert.rozee
author_rank: Frequent Contributor
timestamp: July 25, 2025, 04:49:49 pm
content: Quote from: edavid on July 24, 2025, 08:54:11 pmNO!!!!please do NOT do this, those front-panel switches are NOT rated to handle 120vAC and there will beinsufficientphysical clearance between the AC mains wiring and the multimeter's electronics. end result will be potential for mains voltages to end up on the meter's input terminals - you will turn your Fluke 8000A into a death trap just waiting to happen.there is a good reason why manufacturers use the likes of plastic push-rods that actuate a separate (mains rated) switch sitting way back near the rear panel. see, for example, the construction of the HP 34401A or Fluke 8842A.cheers,rob :-)

author: edavid
author_rank: Super Contributor
timestamp: July 25, 2025, 04:57:54 pm
content: Quote from: robert.rozee on July 25, 2025, 04:49:49 pmThat would make sense except for the fact that the non-battery version of the 8000A routes the AC power to the same switch. There is no push rod. It's arguably even less safe since the line voltage is routed on PC board traces instead of insulated wires. However, if you don't want to do it, it's fine, the meter will just draw power when turned off.

author: robert.rozee
author_rank: Frequent Contributor
timestamp: July 25, 2025, 05:01:27 pm
content: Quote from: edavid on July 25, 2025, 04:57:54 pmare you able to post an image of the AC-only PSU schematic?cheers,rob :-)

author: edavid
author_rank: Super Contributor
timestamp: July 25, 2025, 05:02:44 pm
content: Quote from: robert.rozee on July 25, 2025, 05:01:27 pmSee the first message in this thread

author: floobydust
author_rank: Super Contributor
timestamp: July 25, 2025, 05:27:17 pm
content: I added it to Post #4.It's always on, charging the battery.For the AC-only power version , they seem to be switching Neutral. This is 1972.

author: robert.rozee
author_rank: Frequent Contributor
timestamp: July 25, 2025, 05:41:10 pm
content: looking at the manual from here:https://assets.fluke.com/manuals/8000a___imeng0100.pdfthe battery and AC-only versions seem to use different PCB layouts, compare pages 74 and 75 of the above linked PDF, also see section 5 (pages 39 and 40). i would expect/hope that S12 (the power switch) differs between the two versions, as well as that the track layout carrying the AC mains to the switch would be routed with sufficient clearances.does anyone have a photo of the underside of the AC-only version's PCB?cheers,rob :-)

author: edavid
author_rank: Super Contributor
timestamp: July 25, 2025, 06:08:54 pm
content: Quote from: robert.rozee on July 25, 2025, 05:41:10 pmThe BOM is in the manual (page 37) - S12 is the same for both versions.

author: robert.rozee
author_rank: Frequent Contributor
timestamp: July 25, 2025, 06:32:05 pm
content: Quote from: edavid on July 25, 2025, 06:08:54 pmi had noticed that BOM, but it made no sense for the battery version as all 12 switches are clearly asingleassembly in all the photos i've been able to find - including the photo in reply #3 of this thread. my conclusion is that that BOM is most likelyjustfor the AC-only version; i could see no BOM that gave "S1-S12" as asinglecomponent.cheers,rob :-)

author: coromonadalix
author_rank: Super Contributor
timestamp: July 25, 2025, 06:33:55 pm
content: even if the design differit is possible with say some dc-dc converters / dual output ones etc ... to fitif the pcb as the dual x-former output, maybe some trick to do with the power switch an an added small relay, no ac main would give some contact options say : battery only until it dries out, and with ac main the relay does open a section while helping the battery chargeyou do need the +/- 15 volts and the 5 volts, the 5volts must be around 1 amp or more ? is it possible to measure it ?

author: edavid
author_rank: Super Contributor
timestamp: July 25, 2025, 06:44:51 pm
content: Quote from: coromonadalix on July 25, 2025, 06:33:55 pmI don't understand this, can you clarify?QuoteThe 5V current is about 450mA. The +/- 15V is generated by the DC-DC converter from the 5V supply.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 25, 2025, 11:38:49 pm
content: Quote from: coppercone2 on July 24, 2025, 10:04:01 pmWhile this was my very first DMM, I can't say I disagree.https://www.eevblog.com/forum/repair/is-a-fluke-8000a-worth-repairing/

author: robert.rozee
author_rank: Frequent Contributor
timestamp: July 26, 2025, 12:01:01 am
content: just found a rather telling comment regarding Fluke's handling of mains voltages in the 8000A here:https://www.eevblog.com/forum/repair/is-a-fluke-8000a-worth-repairing/msg5090572/#msg5090572Re: Is a Fluke 8000A worth repairing?« Reply #11 on: October 03, 2023, 04:14:18 am »Quote from: bd139 on October 02, 2023, 03:14:18 pmthis leaves me thinking that even the AC-only versions of the 8000A should be reworked to bring the handling of mains in line with modern safety design practices.cheers,rob :-)

author: joeqsmith
author_rank: Super Contributor
timestamp: July 26, 2025, 12:23:20 am
content: Really, who is ever going to use one? After I rebuilt mine, it's packed away in a box. The only value it really has it that it was my first digital meter. If not for that, running it over with the car would certainly be a good use.

author: edavid
author_rank: Super Contributor
timestamp: July 26, 2025, 01:13:09 am
content: Yes, every thread must be derailed with irrelevant comments.But to answer your question, I've given a couple of them away to EE students, and they seemed happy enough.Why don't you take yours out of the box and give it away?

author: floobydust
author_rank: Super Contributor
timestamp: July 26, 2025, 01:36:10 am
content: It's over 50 years old. Among the first LED display bench DMM's.All vintage gear- test equipment, even tube radios, guitar amps are from an era where the safety standards were quite basic.Many other makes of test equipment also use these push switches. Taiwan builds useAlps SPUNwhich are pretty wimpy 1A 25VDC but the power transformer is always energized by mains. They'll just switch the LV DC side.But in this thread the issue is someone's mod - running mains to the on/off switch that was previously switching low voltage from the battery. Making the -01 into a -02.The battery-powered meter is a different PCB and spacings to the switch is not fully known.For Fluke, it is mains Neutral those pcb traces that run to the front panel on/off switch- so not a major source of hum. Next few models out, I see they fixed it better using a separate switch for mains power, spaced away from the other switches.For the 8000a I would consider just adding a mains on/off switch at the rear panel, and the 5V regulator.Since OP is just starting out, it might be better to work on this vintage multimeter later on, put it away and for now buy a low dollar handheld DMM?

author: AVGresponding
author_rank: Super Contributor
timestamp: July 26, 2025, 08:20:54 am
content: I wouldn't run the mains to the power switch on the battery model. No solder mask, no isolation, just a bad idea.The build quality is so poor you'd struggle to believe it's actually a Fluke. Compare it to the 8125A, for instance:The charger is pretty much the same, but the traces are gold plated, the isolation spacing is good, it has good quality components etc.Funny you should mention bd139, he's a proper curmudgeon about these, but he's actually fixing a Heathkit counter with similar build quality at the momentI was chatting with him while fixing a recently acquired HP 3457A last night (A2 C911, U921 both short), and we were both admiring the general build quality, in fact he was wishing he'd bought that instead

author: joeqsmith
author_rank: Super Contributor
timestamp: July 26, 2025, 03:46:36 pm
content: Quote from: edavid on July 26, 2025, 01:13:09 amI only kept it because it was my first DMM, and has sentimental value. As far as meters go, the 8000A is on par with the free meters HF gives away. In many ways the free HF meter is superior.

author: floobydust
author_rank: Super Contributor
timestamp: July 26, 2025, 07:40:38 pm
content: I think your price point is a little too lowThe HF meter, DT-830 is true piece of shit I got one freebie at a trade show (Taiwan build) and the rotary switch seems to be malfunctioning and I even wasted moments of my life cleaning it, adding the missing protection transistor. Lasted about 4 months, it's gone in the trash.At least beat the Great grandpa Fluke 8000a. Even the Brymens won't be running after 50 years lol.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 26, 2025, 08:25:49 pm
content: Quote from: floobydust on July 26, 2025, 07:40:38 pmThe cost back then to repair the 8000A it seems was about $75 (back then) which included a few ICs and sorted passive parts. The Fluke 8000a has no input protection and is easily damaged. After I damaged mine a second time, I bought a brand new HP 3468A (which is still running today). Cost wise, that Fluke may have been the most expensive meter to own and operate. I also bought a DT-830 at Sears that I used in the garage for several years until the LCD failed. That may have been the cheapest least expensive meter I bought.No doubt any meter's life will depend a lot on how it is used. Personally, I would never buy another princess meter like that Fluke again. It was very expensive and far too frail. While there still is a lot of low end meters available today that have no input protection and cost very little, there are also products that are very electrically and mechanically robust. Pretty much anything out there today will out perform the 8000A.

author: Vonsgarage
author_rank: Contributor
timestamp: July 26, 2025, 09:02:16 pm
content: Original Poster Here:Wow! My settings to receive notifications of replies must have been set to off!Please let me catch up on all the replies you wonderful folks have written. And also accept my apology for the giant schematic. Looks like another thing I'm not skilled in. Let's try again:This is a "End-of-post expandable thumbnail". Fingers crossed.

author: floobydust
author_rank: Super Contributor
timestamp: July 26, 2025, 09:10:47 pm
content: Quote from: joeqsmith on July 26, 2025, 08:25:49 pmIt's true- this is a fragile multimeter. They all were, in the 70's.As I mentioned, it's not so great for people starting out in electronics because it can get zapped and read wonky or need difficult repairs. This gets in the way of learning and doing the craft.

author: Vonsgarage
author_rank: Contributor
timestamp: July 26, 2025, 10:21:15 pm
content: Caught up. Never ceases to amaze me. You folks ever have a question about HVAC I owe you all one.I have once again whipped up a drawing that I will use with the modification performed by edavid. I'll open her (the 8000a is a her?) up tomorrow and try to copy my unit / edavid's unit's photos / and the schematic and see if I can finish up the drawing and add the battery schematic tie-in points.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 26, 2025, 10:43:39 pm
content: Quote from: floobydust on July 26, 2025, 09:10:47 pmThe Fluke cost me some major cash back then. My first Radio Shack analog meter was maybe a 1/10th the price and while I did damage it several times, I was able to repair it for pennies. Looking back, it was a very poor choice.

author: floobydust
author_rank: Super Contributor
timestamp: July 26, 2025, 10:46:40 pm
content: I'm totally jealous, I had no money and ended up with a Sabtronics 2000

author: joeqsmith
author_rank: Super Contributor
timestamp: July 27, 2025, 01:03:34 am
content: Quote from: floobydust on July 26, 2025, 10:46:40 pmI have a friend who worked there and built that kit. He recently gave it to me. Did you build yours?

author: floobydust
author_rank: Super Contributor
timestamp: July 27, 2025, 05:38:15 pm
content: I built mine from the kit, still have it, still works. You don't forget your early test equipment. Sabtronics was in Dallas. 6V 150mA power. It uses a triac crowbar to protect the current shunt. In the day, 7-seg LED prices were fast dropping as well as A/D converter IC's appeared. Only other multimeter kits I recall are the Sinclair.John Fluke Sr. was in his 60's when the 8000A rolled out. Custom silicon used. Some aspects are impressive.Went to a show'n'shine, see a stock 1951 Mercury Coupe with a flathead V8.Do I give the old guy a hard time - there's no seatbelts, no airbags, no ABS, "the car is unsafe" kind of lecture?

author: joeqsmith
author_rank: Super Contributor
timestamp: July 27, 2025, 06:19:59 pm
content: Quote from: floobydust on July 27, 2025, 05:38:15 pmI think they had moved to Florida when my friend worked for them.I always wonder why people on this site want to use cars for an analogy. No matter. First, I doubt many people are driving around in cars built from the 50s and racking up 50k miles a year on them. I would imagine in some states, they would ticket you for not having proper safety equipment. Some people just collect them for a fun show car. Like our little princess and the pea meter, it's not very useful and more just a nostalgic collectible who's day has come and gone.I had a friend who raced vintage cars. A gentlemen's sport. They had to keep everything per period when the car was originally raced, except for safety. The cars were modified and inspected. Without the proper mods, they were not allowed to compete.My vintage motorcycles don't have a lot of safety requirements. If they are slow enough, I think you could just run them stock. At some point, they want a tether switch (dead man switch), 2" of ground clearance, diaper. Of course, current certification for helmet, gloves, zipped together or one piece leathers. You also need to have a valid competition license. The license changes depending on the speeds you drive at.

author: floobydust
author_rank: Super Contributor
timestamp: July 28, 2025, 02:30:35 am
content: Quote from: Vonsgarage on July 26, 2025, 09:02:16 pmCareful, some parts on the PC board are hazardous live, like the fuse & holder, transformer pins on one side, a few PCB traces, IEC power entry etc.So there is a shock hazard on this project and you mentioned not having a lot of experience, so I'll advise to use care or bail out.I'd think of locating the 5V reg board away from all that, on the other corner? The input (-) I'd connect at the transformer center tap.You might be able to use lead or solid wire pins as legs to secure the 5V board to the main board. But I don't have one in front of me to look at, which pads to use.You just don't want the board loose inside flopping around, it could touch hazardous live stuff.Also the MP1584 board has solder jumpers on the backside, blob the "5V" one, and remove the blob across "ADJ" and all others. To set it to fixed 5V output.

author: robert.rozee
author_rank: Frequent Contributor
timestamp: July 28, 2025, 02:59:35 am
content: Quote from: floobydust on July 28, 2025, 02:30:35 amit may be worth thinking about ripping out ALL the mains stuff, and simply replacing the mains socket on the back with a 5v USB socket through which the meter is to be powered.cheers,rob :-)

author: Vonsgarage
author_rank: Contributor
timestamp: July 29, 2025, 12:28:32 pm
content: I modified the battery version schematic and used the idea of adding a mess of MP1584's. Threw in some capacitors. Am I nuts thinking this will work?I will pull the thing apart today and see if I can find elegant locations on the PCB to tie in all this stuff. Lots of room inside to add the modules securely / safely.MODIFIED the originally posted schematic.Since the modules are around a buck-a-piece, cost vs ROI is OK.

author: edavid
author_rank: Super Contributor
timestamp: July 30, 2025, 04:00:04 pm
content: Quote from: Vonsgarage on July 26, 2025, 09:02:16 pmNope, you need to resize the image to something sensible. You can still fix your first message with the Modify button. Remove the enormous image and attach a new one. Do the same thing with your latest post.Quote from: robert.rozee on July 28, 2025, 02:59:35 amIf you use external power for a multimeter, it is hard to figure out the safe floating voltage, especially if you are using an unspecified USB power supply.If you use the original Fluke transformer, the spec is 1200V peak. You aren't going to get close to that with external USB power.Quote from: Vonsgarage on July 29, 2025, 12:28:32 pmYes, you are nutssince the meter is designed to work without regulators on the +/-15V lines. Why did you you think you needed to add those?

author: Vonsgarage
author_rank: Contributor
timestamp: July 30, 2025, 05:16:16 pm
content: edavid: Nice to hear from you again.Learning.Image on original post better. I'll do better next time I join you folks for help.Separate PS? Good point about floating grounds. I found that out while fooling around with an Audiometer and trying to repurpose as a test oscillator. Magic Smoke!And after thinking about using three modules (of course, after I had made a cool mounting board) it dawned on me I just need to get +5 to the beginning of the OEM PS and let Mr. Fluke take care of everything the way it has been doing for the last 50 years.