$10 Fluke 233 - Corrosion Repair and Testing

[CarsonReidDavis]

I bought broken Fluke 233 for $10. The head unit turned on, but it read rF Err and would flash and then turn off.

So I opened it up and found corrosion all over the PCB which I cleaned off with q-tips and isopropyl alcohol. However it still didn't work. So I gave it a really close inspection and found a tiny short made of blue corrosion which I confirmed with a continuity test.

Alcohol and q-tips made no impact on this last bit of corrosion, so I finished the cleaning with a plastic dental scraper and a magnifying glass. Reassembled, the Fluke now appears to work perfectly. [UPDATE: this did not fully resolve the issue, see below]

I uploaded a full album of photos and descriptions at https://imgur.com/a/xoucQ2G.

Now I want to test the unit to see if it is still accurate with all the various readings. I have power supplies, resistors, batteries, oscilloscopes, other multimeters, etc, but nothing I would consider lab grade calibrated. Are there any standard methods for this type of accuracy and functionality testing?

[retiredcaps]

I bought broken Fluke 233 for $10.

Great bargain.

Now I want to test the unit to see if it is still accurate with all the various readings.

Modemhead has repaired a lot of Fluke corrosion issues at

http://mrmodemhead.com/

and it is rare that the Fluke is out of calibration due to corrosion.  The 233 is a newer Fluke so its calibration constants would be stored in some chip.

As long as the 233 reads similar to another meter, I would consider it fine.

Alternatively, you can contact some independent calibration lab, pay around $60 to $100 to get it tested.

[retiredcaps]

R127 looks like there is some blue corrosion left.  I would heat up the soldering iron, apply flux and just touch up R127.

[CarsonReidDavis]

Is it dangerous to leave unattended corrosion? Or is it just the likelihood that that solder joint is now weak and might open in the future?

For instance, can it propagate on its own if I don't remove it?

[retiredcaps]

Is it dangerous to leave unattended corrosion?

Eventually, I don't know when, it will/may affect the resistor.

Or is it just the likelihood that that solder joint is now weak and might open in the future?

For instance, can it propagate on its own if I don't remove it?

I don't know since I don't have it in front of me, but if you can reflow with flux, that will ensure R127 is good.

[coromonadalix]

i would clean it toroughly with an horse hair tooth brush   and put some pcb protection against oxydation :  like an pcb varnish, clear cutex  ... easy to remove if ...

[tooki]

Is it battery leakage? If so, then it’s probably alkaline and you need to use an acid (like white vinegar) to neutralize it. If it’s acid corrosion, then you neutralize with an alkaline (like baking soda). In both cases, then rinse thoroughly with distilled water, and then with IPA.

[CarsonReidDavis]

The seller told me that the damage was caused by batteries that had been left in the unit and corroded. I assume Alkaline but don't know for sure.

I didn't have any vinegar in the house when doing the initial clean. I'll go buy some and see if that removes the remaining corrosion. I assume I will have to do a secondary clean with alcohol to remove the vinegar?

[bob91343]

Ever since my favorite solvent turned out to be a hazardous substance I have bemoaned its unavailability.

[CarsonReidDavis]

Yeah, I have been pretty fond of dihydrogen monoxide for general cleaning around the house. However someone recently informed me that there is a large body of evidence that most organisms that come into contact with the substance eventually die.

Shockingly, the solvent is still readily available, so I still use it for my cleaning.

[retiredcaps]

The seller told me that the damage was caused by batteries that had been left in the unit and corroded. I assume Alkaline but don't know for sure.

I use Eneloops ni-mh in all my meters that take AA.

[tooki]

The seller told me that the damage was caused by batteries that had been left in the unit and corroded. I assume Alkaline but don't know for sure.

I didn't have any vinegar in the house when doing the initial clean. I'll go buy some and see if that removes the remaining corrosion. I assume I will have to do a secondary clean with alcohol to remove the vinegar?

As I said, afterwards rinse generously with distilled water, then with alcohol (or solvent based flux remover, PCB cleaner, etc).

[Shock]

Ever since my favorite solvent turned out to be a hazardous substance I have bemoaned its unavailability.

Trichloroethylene/Tetrachloroethylene?

[CarsonReidDavis]

I have recently discovered that the unit is not totally repaired. Although it turns on and gives accurate DC voltage readings, further testing has shown that it has about 20% error in AC voltage and 10% error when measuring large resistances.

When previously repairing it, I was unable to fully remove the PCB from the case to examine the back of the board. I assume there must be more corrosion on the back that needs to be removed.

I have since purchased distilled white vinegar and 99.9% electronics grade isopropyl. I will be updating this thread with more pictures when I begin the repair.

[CarsonReidDavis]

I was able to fully disassemble the meter and gain access to the back of the PCB. I found significant corrosion there on the leads of what appears to be the main IC. After significant cleaning with vinegar and rinsing with isopropyl, I reassembled the unit. Testing against large resistors and AC voltages now seems completely accurate.

If anyone wishes to undertake a similar task, there were a couple of key tricks to the full disassembly. First, the rotating knob is connected through the PCB. I pried it off while simultaneously using tweezers to loosen the connecting clip. The difficulty of this step was what originally prevented me from a full disassembly. It would be very easy to break this piece off, but it was much harder to remove it in a way that it could be put back together.

Secondly, there are a couple of plastic clips innocuously holding the PCB into the case. They need to be pushed out of the way to remove it safely.

I have added around 10 more close-up pictures of the cleaning to the original album with descriptions.  https://imgur.com/a/xoucQ2G