Author Topic: Fluke 8050A repair  (Read 2578 times)

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Offline MikeK

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Fluke 8050A repair
« on: June 03, 2022, 11:11:35 pm »
Anyone know where I can get an amps socket for my as-is eBay purchase?

Doesn't have:
[attachimg=1]

Should have:
[attachimg=2]

EDIT: Changed title to reflect current status.
« Last Edit: June 05, 2022, 01:41:37 pm by MikeK »
 

Online bdunham7

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Re: Fluke 8050A amps jack
« Reply #1 on: June 03, 2022, 11:41:42 pm »
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.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline MikeK

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Re: Fluke 8050A amps jack
« Reply #2 on: June 04, 2022, 12:47:24 am »
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.

[attachimg=1][attachimg=2]
 

Online bdunham7

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Re: Fluke 8050A amps jack
« Reply #3 on: June 04, 2022, 01:20:00 am »
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...
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Online Martian Tech

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Re: Fluke 8050A amps jack
« Reply #4 on: June 04, 2022, 03:03:58 am »
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).
« Last Edit: June 04, 2022, 03:08:27 am by Martian Tech »
 

Online bdunham7

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Re: Fluke 8050A amps jack
« Reply #5 on: June 04, 2022, 04:04:01 am »
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).

That'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.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline MikeK

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Re: Fluke 8050A amps jack
« Reply #6 on: June 04, 2022, 02:00:44 pm »
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.
 

Online Martian Tech

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Re: Fluke 8050A amps jack
« Reply #7 on: June 04, 2022, 03:58:57 pm »
Oops.  I'm an idiot... :palm:
 

Online bdunham7

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Re: Fluke 8050A amps jack
« Reply #8 on: June 04, 2022, 05:01:13 pm »
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.

So 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. 
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline MikeK

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Re: Fluke 8050A amps jack
« Reply #9 on: June 04, 2022, 07:19:04 pm »
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.

So 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.

A 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.)
 

Online bdunham7

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Re: Fluke 8050A amps jack
« Reply #10 on: June 04, 2022, 07:25:25 pm »
The display IC voltages appear correct, but having a board to drop right in would certainly be nice before doing the conversion. 

That 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.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline MikeK

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Re: Fluke 8050A amps jack
« Reply #11 on: June 05, 2022, 02:30:09 am »
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.
 

Online bdunham7

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Re: Fluke 8050A amps jack
« Reply #12 on: June 05, 2022, 03:50:04 am »
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.

I 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.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline MikeK

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Re: Fluke 8050A amps jack
« Reply #13 on: June 05, 2022, 10:59:51 am »
Thanks.  Don't send anything yet.  I'll continue with testing.
 

Offline MikeK

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Re: Fluke 8050A repair
« Reply #14 on: June 05, 2022, 01:43:51 pm »
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.
 

Online bdunham7

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Re: Fluke 8050A repair
« Reply #15 on: June 05, 2022, 01:57:45 pm »
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.

I'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.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline MikeK

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Re: Fluke 8050A repair
« Reply #16 on: June 05, 2022, 02:07:56 pm »
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.

I'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.

From 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..
 

Online bdunham7

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Re: Fluke 8050A repair
« Reply #17 on: June 05, 2022, 02:29:11 pm »
From the schematic it looked like the second transformer was creating a floating supply for the processor.

But 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.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline MikeK

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Re: Fluke 8050A repair
« Reply #18 on: June 05, 2022, 03:13:48 pm »
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.
 

Offline MikeK

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Re: Fluke 8050A repair
« Reply #19 on: June 05, 2022, 05:02:03 pm »
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.
 

Online bdunham7

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Re: Fluke 8050A repair
« Reply #20 on: June 06, 2022, 03:54:44 am »
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.

OK, shall I send out the display board and socket/fuse bit then? 
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline MikeK

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Re: Fluke 8050A repair
« Reply #21 on: June 06, 2022, 12:45:03 pm »
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.

OK, shall I send out the display board and socket/fuse bit then?

Yes, thank you. :)  I've already started work on a replacement display.
 

Offline MikeK

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Re: Fluke 8050A repair
« Reply #22 on: June 15, 2022, 12:50:22 pm »
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.

[attach=1]
« Last Edit: June 15, 2022, 12:55:14 pm by MikeK »
 

Offline MikeK

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Re: Fluke 8050A repair
« Reply #23 on: June 18, 2022, 07:34:40 pm »
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...
« Last Edit: June 19, 2022, 02:58:31 pm by MikeK »
 

Offline MikeK

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Re: Fluke 8050A repair
« Reply #24 on: June 18, 2022, 07:56:35 pm »
Better image:
« Last Edit: June 19, 2022, 02:57:32 pm by MikeK »
 


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