Fluke 8050A repair - Page 1
Forum section: electronics / repair

author: MikeK
author_rank: Super Contributor
timestamp: June 03, 2022, 11:11:35 pm
content: Anyone know where I can get an amps socket for my as-is eBay purchase?Doesn't have:Should have:EDIT: Changed title to reflect current status.

author: bdunham7
author_rank: Super Contributor
timestamp: June 03, 2022, 11:41:42 pm
content: There should be some lurking in my garage somewhere. If you just got this unit , look it over and note any other bits you might need and then post or PM me.

author: MikeK
author_rank: Super Contributor
timestamp: June 04, 2022, 12:47:24 am
content: That would be great, man. I got this as a learning experience, to fix it. Doesn't power up, or at least the display doesn't come on. I guessed that from the listing and planned on putting in a new display (7-seg or OLED). Nothing else appears missing other than the amps jack. All buttons are there and they operate. The insides looks good to me, nothing burned.

author: bdunham7
author_rank: Super Contributor
timestamp: June 04, 2022, 01:20:00 am
content: To start, don't assume the display is bad and don't mess with it until you've gone over the rest of it and it all seems to be powering up and working. Usually the displays leak or look bad, not just fail to operate at all. Of course YMMV, especially it if as already been poked at. I may have a functioning display PCB as well--I'll go look tomorrow and see how well I labelled things...

author: Martian Tech
author_rank: Regular Contributor
timestamp: June 04, 2022, 03:03:58 am
content: Note the BAT CHG light in the second pic.Probably the reason it doesn't work is that the batteries have been removed. It won't operate without them unless you make some mods (convert the battery-charging current source to a voltage source).

author: bdunham7
author_rank: Super Contributor
timestamp: June 04, 2022, 04:04:01 am
content: Quote from: Martian Tech on June 04, 2022, 03:03:58 amThat's someone elses. His meter looks like a non-battery model--the area below and to the right of the transformer has a bunch of unpopulated positions where the battery charging circuit would be.

author: MikeK
author_rank: Super Contributor
timestamp: June 04, 2022, 02:00:44 pm
content: Correct, mine is the non-battery model. It does power up. And all the test points/voltages check out. The display just went bad...it's all black. If I can find an amps jack for cheap then I can add in an LED display and put it on the bench.

author: Martian Tech
author_rank: Regular Contributor
timestamp: June 04, 2022, 03:58:57 pm
content: Oops. I'm an idiot...

author: bdunham7
author_rank: Super Contributor
timestamp: June 04, 2022, 05:01:13 pm
content: Quote from: MikeK on June 04, 2022, 02:00:44 pmSo it appears that I have two half-eaten disassembled parts units, one battery-type and one not. I have the fuse holder/jack part. I also have a display board that appears functional--when I power up the remnants of the meter it doesn't 'work' but the display appears clear and all the segments come on. So I'd recommend just swapping the entire display PCB to maybe get a working unit and then if you want to purse the LED-conversion with your old PCB you can. If you come up with a good LED conversion I'd appreciate a copy of the files and so forth as I have a couple of working units as well.The parts are yours for shipping costs only.

author: MikeK
author_rank: Super Contributor
timestamp: June 04, 2022, 07:19:04 pm
content: Quote from: bdunham7 on June 04, 2022, 05:01:13 pmA generous offer...Thank you, sir. I'm assuming the fuse holder/jack just pushes in and rotates into the correct position...I don't need anything else. I do need the fuse, though. The back side of the socket appears all there...The receptacle with the spring-loaded wire. The display IC voltages appear correct, but having a board to drop right in would certainly be nice before doing the conversion. I'll certainly post what I wind up doing. (I'm quite impressed with how well-built and straightforward this device is and how it will be to convert the display.)

author: bdunham7
author_rank: Super Contributor
timestamp: June 04, 2022, 07:25:25 pm
content: Quote from: MikeK on June 04, 2022, 07:19:04 pmThat was my thought--have a working one installed and another to modify. The boards are easy to swap in and out.As for the fuse holder, the other part is integral to the front panel--if the slotted tube, wire and spring are all in there, it should be fine. I've got the front insert and fuse.PM me your address and I'll send it out next week.

author: MikeK
author_rank: Super Contributor
timestamp: June 05, 2022, 02:30:09 am
content: I may also order a processor from China. I rechecked the display voltages and *all* of the segments are ON...and the processor is outputing the 50Hz refresh signal. I'll scope the BCD outputs tomorrow. I did remove the display to make sure it wasn't interfering.

author: bdunham7
author_rank: Super Contributor
timestamp: June 05, 2022, 03:50:04 am
content: Quote from: MikeK on June 05, 2022, 02:30:09 amI wouldn't jump to the conclusion that U17 is bad, a problem on the board or with the interconnect ribbon could cause it. I've seen the 'all segments' issue before on disassembled meters, possibly bad connections or something are at fault. It usually goes away, TBH--so I don't recall any specific fix. But if you decide you need a U17, let me know and I'll tuck one in the box.

author: MikeK
author_rank: Super Contributor
timestamp: June 05, 2022, 10:59:51 am
content: Thanks. Don't send anything yet. I'll continue with testing.

author: MikeK
author_rank: Super Contributor
timestamp: June 05, 2022, 01:43:51 pm
content: I don't think I have a way to check the processor, as it runs off a floating supply and I don't have an isolation transformer. Suggestions? I guess I could make a quickie display with an Arduino and tiny OLED to grab whatever is on the processor BCD outputs.

author: bdunham7
author_rank: Super Contributor
timestamp: June 05, 2022, 01:57:45 pm
content: Quote from: MikeK on June 05, 2022, 01:43:51 pmI'm not sure what you mean by a 'floating supply'. The power supply transformer supplies isolation except for the 47M static drain resistor. You can ignore that, or just use a two-prong plug for more complete isolation. The processor is driven by the -5V supply, but if you are using a scope or meter, this isn't an issue. You can just consider the -5V as ground, or you can look at inverted signals. How were you planning on testing U17 in any case? If it is putting out the BP signal it would seem that it is alive.

author: MikeK
author_rank: Super Contributor
timestamp: June 05, 2022, 02:07:56 pm
content: Quote from: bdunham7 on June 05, 2022, 01:57:45 pmFrom the schematic it looked like the second transformer was creating a floating supply for the processor.I was going to test the processor BCD outputs for activity. I have since verified that the connections from the processor socket to the display board traces (after the ribbon cable) have good continuity so that's not an issue..

author: bdunham7
author_rank: Super Contributor
timestamp: June 05, 2022, 02:29:11 pm
content: Quote from: MikeK on June 05, 2022, 02:07:56 pmBut yours should only have one transformer? The schematic may be confusing you because they show the battery and non-battery model together and it isn't clear that you only have one or the other. If you look at the schematic you'll see Q5, T3, CR5, etc. Those and everything below and to the left of them do not exist in your unit.

author: MikeK
author_rank: Super Contributor
timestamp: June 05, 2022, 03:13:48 pm
content: Okay, fears allayed. Yeah, I just assumed that transformer was a floating supply for the micro and didn't even think that the physical board doesn't have it. So, there is data on the BCD lines, albeit slowly.

author: MikeK
author_rank: Super Contributor
timestamp: June 05, 2022, 05:02:03 pm
content: Another fear allayed, I think. After digging into the datasheet for the display driver IC's...all display segments are strobed and the OFF segments are 180 deg out of phase with the ON segments. So it would, in fact, *appear* to have all segments on when testing only with a DMM.

author: bdunham7
author_rank: Super Contributor
timestamp: June 06, 2022, 03:54:44 am
content: Quote from: MikeK on June 05, 2022, 05:02:03 pmOK, shall I send out the display board and socket/fuse bit then?

author: MikeK
author_rank: Super Contributor
timestamp: June 06, 2022, 12:45:03 pm
content: Quote from: bdunham7 on June 06, 2022, 03:54:44 amYes, thank you.I've already started work on a replacement display.

author: MikeK
author_rank: Super Contributor
timestamp: June 15, 2022, 12:50:22 pm
content: Yes, I have been working on this. I still have some wiring to do and finding a display. I made a carrier board to plug into the Fluke's processor socket to allow me to piggyback a uC for grabbing all of the data signals. I'll probably create a separate thread for this since it's more of a project than a repair. There's also information about how the factory display works that might be useful to others.

author: MikeK
author_rank: Super Contributor
timestamp: June 18, 2022, 07:34:40 pm
content: Got a display working. Some hair pulling before I realized I wired the data bus backwards. Sorry for the poorly focused image; my phone couldn't get the OLED in focus. And I still have to wire for DP and HV. dB and REL actually use the DP signal, so it's just coding. Also wiring for the mode and range switches...that's nice to have on the display.And, no, this isn't the final solution; that display is way too small. I might go for a TFT that fits into the case opening. And then I can add cool stuff like MIN/MAX, trend plots, and data logging. Would be nice if those TFT's came with I2C interface. Using a 28-pin PIC doesn't leave many pins left.I deserve a chai and a cookie now...

author: MikeK
author_rank: Super Contributor
timestamp: June 18, 2022, 07:56:35 pm
content: Better image:

author: MikeK
author_rank: Super Contributor
timestamp: June 19, 2022, 02:59:07 pm
content: Made a bigger font for it. Still to small, I think.

author: bdunham7
author_rank: Super Contributor
timestamp: June 19, 2022, 03:24:27 pm
content: Even at that it will be much easier to read than the original. By modern standards those original displays are pretty bad.

author: MikeK
author_rank: Super Contributor
timestamp: June 19, 2022, 03:46:56 pm
content: I still like an LED solution to this. I really like 7-seg. Very fitting for the style and age of the 8050A. It's limiting in what can be displayed, though. Looks like I can get a larger version of this simple OLED (2.4" v. 1.3") for around $15. The TFT displays seem to come in a appropriate size for less money, and it's color too. But many more pins involved in the comm interface. I used what I had on hand, a 28-pin PIC18F26K40. About 20 pins get used up in grabbing the data from the Fluke processor: 4 line data bus, 5 strobes, 1 decimal point, 1 HV, and then 3 for range and 3 for mode if those are desired. Okay, 17...maybe I can fit a TFT and a rotary encoder.

author: Swainster
author_rank: Frequent Contributor
timestamp: June 21, 2022, 02:28:03 am
content: I just bought a '2.4" OLED' for exactly this purpose (i.e. restoring one of my pile of defunct 8050As). Unfortunately the single sample I bought was damaged in transit (was not boxed, just wrapped in foam). Anyway, I can confirm that the 2.42" display that I bought - doesn't - quite fit. It's close, but sadly no cigar. It actually looks like a very nice display so hopefully I'll be able to get a replacement and use it in some other project.I suppose technically, as it's so thin, you could mount the display in front of the original aperture, but my personal preference is something that looks more a bit more "original".

author: MikeK
author_rank: Super Contributor
timestamp: June 21, 2022, 01:23:42 pm
content: Quote from: Swainster on June 21, 2022, 02:28:03 amThanks for posting your experience. Does the display itself not fit or is it because of the PCB? I'm thinking about separating the display from the PCB but still leave it connected.

author: MikeK
author_rank: Super Contributor
timestamp: June 22, 2022, 12:20:24 am
content: Added decimal and mode.

author: bdunham7
author_rank: Super Contributor
timestamp: June 22, 2022, 12:30:48 am
content: Quote from: MikeK on June 21, 2022, 01:23:42 pmI'm thinking you guys might be better off 3D printing a custom display frame instead of trying to match the original.

author: MikeK
author_rank: Super Contributor
timestamp: June 22, 2022, 02:03:13 am
content: I can definitely fab something. No 3D printer, but I do have a mini-mill and plenty of hand tools.

author: Swainster
author_rank: Frequent Contributor
timestamp: June 27, 2022, 07:17:21 am
content: Sorry, got temporarily knocked off my feet by the 'rona but almost back to normal now.Basically the 2.42" display cannot fit in the space where the original display holder fits. I also purchased a slightly smaller monochrome graphic STN type display which came with back-light. I think it should fit nicely, but of course it won't look as nice as OLED or colour LCD, but may have the advantage of lower power consumption.The plan was indeed to replace the original display holder with a 3D printed modified version, and to that end I have modelled the original display holder, but haven't done the mods yet. Actually I wanted to print it out before I mod it, to check for fit, but haven't been able to get around to it yet.

author: Swainster
author_rank: Frequent Contributor
timestamp: June 27, 2022, 11:44:54 am
content: See attachment just in case anyone wants to try printing out the first draft 3D model of the standard F8050A display holder - please note that this is totally unchecked somay notprobably won't fit. Another note, the draft clearances are assuming a resin type printer - I'd highly recommend opening them up for a filament printer. I'm not sure when I'll get around to checking it against the actual Fluke housing and PCB, so i'm posting this in the meantime. If you are brave then you could use the step file to generate dimensions for your own custom holder design.

author: MikeK
author_rank: Super Contributor
timestamp: June 27, 2022, 03:13:20 pm
content: Here's some information on the Fluke's display, in case it's helpful to anyone...* The LCD is controlled directly by the Fluke's processor, with the display data being latched with CMOS LCD drivers.* The data bus consists of lines W, X, Y, Z; which is 23, 22, 21, 20respectively.* HV and DP lines are also part of the data.* The BP signal is a 50Hz signal only used for refreshing the stock display. Not needed for a custom display.* Display data is latched with positive pulses on one of the five strobe lines (ST0 - ST4).* Data is valid on both rising and falling edges of the strobe pulse. (I grab the data on the rising edge.)* Strobe 0 (ST0) latches data for U10, which handles the HV, BT, and REL indicators.* A high on DP during ST0 indicates REL.* The battery (BT) signal comes from a voltage dividier and PNP. I don't use this, since my Fluke doesn't have those components.* ST0 also latches data for U11, which handles the plus(+), minus(-), 1 (first digit), and the dB indicator. W line is for minus(-), X is for plus(+), Y is for dB, and Z is for the "1". Note that the plus(+) is actually two segments, so W *and* Y together turn on the plus.* ST1 latches data for U12, which is the second digit (first whole 7-seg digit).* ST2 latches data for U13, which is the third digit.* ST3 latches data for U14, which is the fourth digit.* ST4 latches data for U15, which is the fifth digit.* U16 handles the decimals, and is latches by each of the strobes (ST1 - ST4).* The display-only data can be taken from the display board ribbon, or rather the vias right next to it.* Functions (Volts, Amps, Ohms...) are only available at the Fluke processor (which is why I made a carrier board).* Ranges (2, 200, etc.) are also only available at the Fluke processor.* The Vss pins of the chips runs at -5V.* The Vdd pins of the chips runs at 0V.* Display data is latched in sequence: ST0, ST1, etc.* A strobe pulse is about 168us wide, though I observed some at 116us. This isn't really useful anyway.* There is about 216us between the falling edge of one strobe to the rising edge of the next.* One cycle is pretty short, so it makes sense to grab all the data and then process it after ST4 is done.* The whole cycle repeats about every 410ms.Range switch logic (pins are of Fluke 40-pin processor):Pin 3Pin 4Pin 5RangeRngARngBRngC200 ohmHHL2k ohmLHH20k ohmHLH200k ohmLLH2000k ohmHHH2M ohmLLL200 nSHLL2 mSLHL

author: MikeK
author_rank: Super Contributor
timestamp: August 02, 2022, 02:36:17 pm
content: Finally got my TFT display off the slow boat from China. The 2.0" looks to be a good size for the Fluke 8050A's opening. First step was to make sure the display works. It does. And it's a gorgeous display. Gotta love the Arduino community to make these things easy. Hardware SPI is the only way to go, as software SPI is painfully slow. At least for the Arduino Uno. I can run my PIC18F26K40 up to 64MHz.Getting this setup, and porting my previous code to C, is going to take me a while...I was using a simple and uncommon compiler to get the OLED up and running that I'm sure nobody else would use.