Fluke 8050A Repair

[emptech]

I purchased my 8050 brand new when it first came out, I think I paid over $500 for it.  Through the years, had the same issue, the ni-cads would die,would usually short circuit.  I've replaced them from time to time.  Looking at the original circuit, I see it is a constant current source, with two settings.  What it needs is constant voltage, which your mod does, and current limiting.  I see as a constant current source, it is eventually going to cook the batteries.

What was so unique with that meter, the low ohms scale.

I like to keep old equipment alive too -

Jim

[Bassblaster505]

I am having an issue with the mod. I performed the steps that you listed, although my PCB was slightly different than the picture provided. When cutting the trace that connects to U26.1, I had multiple traces (3) ending at U26.1 besides the battery pack. These multiple connections was the transformer, T3, C22, and C34. The cut disconnected those components from U26.1. I take it this is correct, no?

Yes, the cut should simply disconnect U26.1, leaving the rest of the circuit intact.  I've attached a diagram which I hope makes clear exactly how things should be connected before and after, regardless of PCB layout.

Also, after adding the 510 ohm resistor from C23 (negative pin) to U26.1 and plugged in the power cord (after all other steps were performed), I only got a voltage of 4.5V when probing U26.1 and C23 (negative pin), so I ended up upping the resistance to ~650ish ohms to get 5.5V. At this point, I turned it on and nothing appeared on the LCD.

The 5.5V should be from U26 pin 2 to C23 negative pin.  That is the voltage regulator output.  The voltage from U26.1 to C23-neg should be about 1.25V lower than 5.5V, or 4.25V.  Your measurement sounds like it was OK to begin with.  There should be no need to raise the resistor value, which would lead to an output voltage that is too high.

I checked my work a few times and I'm fairly certain I did the steps correctly. When I checked the voltages at TP2, 3, 4, and 5, I don't get the voltages as described in the schematic. I was checking these voltages when having one probe placed on C23 (negative pin) and the other on the test points. The voltages observed were roughly 6V (6.5V on some). But then I thought that I may be placing my other probe, (that connects to C23 negative pin) incorrectly so I placed in on the front panel common plug and the voltages on the test points were in the mV range.

The test point voltages are referenced to the meter ground, which is TP1.  The front-panel common input is also tied to the meter ground.

I think my board is different than both of yours. U26P1 connects to 4 points and i have no clue what i need to do here. my board is Rev R model 8050A-3001

[MickM]

https://www.amazon.com/gp/product/B01N4476AK/ref=oh_aui_search_detailpage?ie=UTF8&th=1
They are slightly smaller than stock, part of a paper napkin stops the rattles.
They work fine, as a bonus it is now portable, and two spares.

Mick M.

[ModemHead]

Pardon my bluntness, but if modding the circuit board presents a challenge, it would be best to solder up a couple of pairs of new NiCd cells, as suggested already.  Sub-C, AA, just about anything will allow the meter to operate normally.

[randalstout]

Wow, thank you so much for this one!  I was about to pull my hair out on the issues.  Power supply, power supply, power supply... 

[kelchm]

Can anyone identify the connectors used on the batteries in the 8050A? I'd like to order some new ones for when I replace the batteries in mine.

[xwarp]

When I replaced the batteries on mine, I just soldered the wires to the tabs on the cells.

[Electro Detective]

Please excuse the Off Topic question:

My 8050A (non battery version) works great at all settings, and agrees with other meters,

except when measuring AC 240 volts mains voltage on the 750V AC Range 

It displays a few volts difference compared to handheld 87v, 8060A and other TRMS meters which all closely agree amongst each other. 

It's not a deal breaker, as a few volts here or there when verifying the mains power is ok, and the 8050A is consistent

I'm just wondering whether that particular AC range is out of calibration,
or 8050A implements a different measuring system,
influence from the high AC bandwidth response,
mains/earth/neutral powered influence
 
or perhaps the 8050A is more on the money with such a measurement 

or maybe it's tweak time...     

   

[kelchm]

When I replaced the batteries on mine, I just soldered the wires to the tabs on the cells.

The connectors on mine are already shot.

I'm sure I could come up with something that would work well, but it would be nice to just be able to buy the correct connector.

[amspire]

It displays a few volts difference compared to handheld 87v, 8060A and other TRMS meters which all closely agree amongst each other. 

When you say a few volts, an error of 2.4 volts is still within the accuracy spec for the 8050A's first year. Given all the decades since then, it could now be a little further off. Get the 8050A manual pdf and if you want to tweak the 750V range to make it the same as the other meters, go for it. I seem to remember there are adjustments to the RMS converter - don't touch those. For most settings, the 8050 stays very accurate over time.

[kelchm]

Can anyone identify the connectors used on the batteries in the 8050A? I'd like to order some new ones for when I replace the batteries in mine.

To answer my own question, the connectors are classified as 1.47mm barrel/bullet connectors.

I can confirm that both of the following from TE Connectivity work well:

• 60940-1 (Digi-Key Part Number A111354CT-ND)
• 60888-2 (Digi-Key Part Number A100338CT-ND)

[kelchm]

I began taking a look at one of my 'broken' Fluke 8050A's tonight and was disappointed to find quite a bit of damage. I think this one will be relegated to the parts pile. At least I got a good LCD out of it.

My question is wether this damage was caused by the caps leaking their guts or by some foreign substance (water?). I ask because I'm wondering if I should proactively replace all the caps in my working 8050A's.

Photos

[Electro Detective]

Open them all up asap, put them side by side for comparison and take PHOTOS,

may as well deal with it     while it's fresh in your mind

Mine is a mains operated unit (non battery model) and last time I looked about 6 months ago everything looked like new inside, no weird caps, smells, or leakage,
everything still in spec 

It may depend on the board revision as to whether some had leak prone caps, or perhaps the internal batteries spewed out clear stuff,
or heat, humidity and moisture issues where the units are parked, or a beer session gone ouch!   

Same deal with the handheld 8060A, later revisions had better or reputable branded capacitors 

[lowimpedance]

Indeed it does look like electrolyte from the nearby cap. Most certainly replace the same caps in your good 8050s as a proactive step.
Perhaps the damaged one can be cleaned up and repaired and join the line up again.

And now you have got me worried, will go and check my 'crew' out right away.

[kelchm]

Open them all up asap, put them side by side for comparison and take PHOTOS

Will do!

I have five of the 8050As, so it will be interesting to take a look at the differences side by side.

[Bashstreet]

That one sure knew how to puke up...

It is hard to say from photos how bad the corrosion is but you might be able to clean it up worth a try any case before you junk it.
If you have same units i would replace that cap on them and maybe recap them fully for peace of mind.

[kelchm]

Wanted to share something I started working on last week. I've been fascinated with the various 8050A display mods since before I even owned one. There's something really cool about taking an old, reliable piece of gear and putting your own spin on it by replacing the entire display.

I've decided to take it one step further and use a 2.4" display rather than the 2.2" Adafruit display that others have used. It's a very snug fit, and I did have to shave about half a millimeter off the bottom tabs on the panel. It's still the same resolution, but I think the end result is going to look great.

Edit: The display in the photo is made by New Haven Display (NHD-2.4-240320CF-CSXN#-F). I really like how solidly built the display is. It even has a metal case/backing which I've never seen on a lcd this small.

[kelchm]

Anyone have any thoughts on what brand/series of capacitors to use when replacing the capacitors on my 8050A's?

I'm considering the Rubycon YXJ series currently since they offer very long life but are not low ESR, which I think would not be desirable in this case.

[marcuswilson007]

I have 3 8050As and none of them will work withot batteries.
When turned off the batteries charge and when turned on they run on the batteries, the batteries do not charge when the meter is operating.
I assume that is to reduce the mains noise getting into the meter while measurements are being made.

[lowimpedance]

And now you have got me worried, will go and check my 'crew' out right away.

Just checked all my 8050's and an 8012 and a 8010.
Of the 3 8050's two are mains only , and I found the
22 uF/16 V caps were just starting to leak. The  220 and 470 microfarad caps
did not show sign's of leakage. I have not investigated the battery model yet as it
contains many more electrolytic's than the mains version.
 As for the 8010 and 12 models both are battery versions and use the same  caps and
I found in both the small 22uF/16 V are also starting corrosion on their pads too.
Note that despite the same value they are not of the same series or manufacturer !.

So this has been a timely reminder to  check old gear with these damn little electro's
otherwise the little bastards will be happily chewing through your favorite gear.
 Many thanks to kelchm for bringing this to our attention, all be it at the expense of one
Of his "50's" (hopefully still salvageable).
 BTW interesting to see the display mod up and running, will look cool I'll bet.

[kelchm]

Just checked all my 8050's and an 8012 and a 8010.
Of the 3 8050's two are mains only , and I found the
22 uF/16 V caps were just starting to leak. The  220 and 470 microfarad caps
did not show sign's of leakage. I have not investigated the battery model yet as it
contains many more electrolytic's than the mains version.
 As for the 8010 and 12 models both are battery versions and use the same  caps and
I found in both the small 22uF/16 V are also starting corrosion on their pads too.
Note that despite the same value they are not of the same series or manufacturer !.

So this has been a timely reminder to  check old gear with these damn little electro's
otherwise the little bastards will be happily chewing through your favorite gear.
 Many thanks to kelchm for bringing this to our attention, all be it at the expense of one
Of his "50's" (hopefully still salvageable).
 BTW interesting to see the display mod up and running, will look cool I'll bet.

Have you begun to pick out replacement caps yet? I’ve been struggling with how to narrow down down what specs I should be looking for beyond the basics.

[lowimpedance]

Have you begun to pick out replacement caps yet? I’ve been struggling with how to narrow down down what specs I should be looking for beyond the basics.

Looking at the schematic only C21 and 24 could be low ESR types, and the rest could be general purpose electrolytics. No need to over analyze it. Just upsize the voltage rating a little since modern
equivalents in the same voltage rating will be quite a bit smaller and the physical mounting may not match the hole spacing.

[Barrelshifter]

I want to describe how I modified the 8050A Revision 3001 PCB for using only with AC Power.
The rev. 3001 board is different to the board showed here to convert the LM317 from current source to regulator mode (5V).
Even the replacement of the LM317 to a LM7805 could not be done directly in the 3001 revision board. This is because of the different layout the pcb has.
The easiest way is to remove the LM317, the batteries and their compartments completely. You do not need them anymore.
The 7805 needs a small heat sink.

It is important, that you place the +5V wire from the 7805 to pinhole 1 AND 2 (bridge). If you miss pin 2, than the meter will not be functional.

I mount the 7805 on the place where one of the batteries was installed before.

See attached schematic for details.

[weejag]

Thank you to Modemhead for posting the best way to modify the 8050A from battery to mains.
The conversion can be done with the other board version.

I have three of the battery versions (two of which are fixable) that require new LED's and which I wish to convert to mains.
The motherboard versions are the 8050A-3001 types so I thought that it might be a help to post pictures of the mod for that particular version.

I have carried out the mod and confirm that it works and gives the required voltages. 
Testing the voltages: test point 1: ground,  test point 2: 13v (actually 14), test point 3: 6v, test point 4: -5v, test point 5: -10v

The mod is the same as ModemHead posted:


R25 does not require removal. Simply short the pins on the solder side.  R26 is replaced with a 150 resisitor.
The 510 resistor is placed on the solder side as shown. Be careful not to short this or the links to anywhere undesirable.

[WimWalther]

Old topic.. but if you landed here, you might just need to know that the battery-option Fluke 8050A will NOT operate with a bad battery pack - even IF it is connected to the AC mains.

If the display just flickers a bit and goes quiet, replace the NiCd batteries, it should fix it.