Multimeter help

[Calidus]

Hi, not sure if this was the correct place to post this but I have an old multimeter that had battery leak corrosion on the battery contacts. I today cleaned them with citric acid (based on recommendations online) and let dry and made sure it was all clean.

 

Now when I put batteries in it (after fully dry) and turn it on, I'm getting lots of random readings on multiple settings without any probes attached, even attached the inputs don't seem to remedy the situation. Only on ohms setting does this not happen. I'm not sure what is wrong as I'm not a big user of multimeters, this one is an old device from my late father and I remember it working fine before leaving batteries in it for a long time period.

 

Could there be ireversvable damage or could something else be wrong? it does have a fuse also. The make and model of the meter is a Soar ME-540 Digital Multimeter.

 

Thanks in advance for any help.

[YoFavRussian]

Did you investigate further inside the meter, I've seen where corrosion will leak into areas and cause issues with traces on PCBs. That would call for a trace repair.

[Calidus]

9 minutes ago, YoFavRussian said:

Did you investigate further inside the meter, I've seen where corrosion will leak into areas and cause issues with traces on PCBs. That would call for a trace repair.

That I did not, so now I will. I'll report back later on what I find and probably take a picture.

[YoFavRussian]

4 minutes ago, Calidus said:

That I did not, so now I will. I'll report back later on what I find and probably take a picture.

Based on your post, it's been sitting in the corrosion for awhile. So I would definitely recommend taking the plastic shell off and giving it a good scrub. And looking over the board pretty well should be pretty obvious if the corrosion has gotten into it.

[Enderman]

Are the batteries you put in brand new?

[Calidus]

2 hours ago, YoFavRussian said:

Based on your post, it's been sitting in the corrosion for awhile. So I would definitely recommend taking the plastic shell off and giving it a good scrub. And looking over the board pretty well should be pretty obvious if the corrosion has gotten into it.

So after taking it apart I see the corrosion went further along the same contacts that was hidden by the plastic so I cleaned those up. (although the cleaning left marks of its own) I couldn't see anymore damage or anything out of place but couldn't look under the board as its firmly in place and I didn't want to break it with unnecessary force.

 

Here's a link to some photos I took below, I'm still waiting on it to dry before trying it again.

 

https://imgur.com/a/8ahUjGP

[Calidus]

2 hours ago, Enderman said:

Are the batteries you put in brand new?

I used fully charged recharble AA batteries, not exactly new though.

[Enderman]

28 minutes ago, Calidus said:

I used fully charged recharble AA batteries, not exactly new though.

Try using alkalines.

[KeyboardCowboy]

5 hours ago, Calidus said:

<snip>

Whats the other side of the board look like? see if you can pop it out, try removing the plastic knob on the front of the meter (carefully).

For future the fuse is 20mm, 200V, 200mA

 

Here is what I have been able to gather so far.

based on the ME-550, it looks like the only thing holding it together is the range selector knob.

Spoiler

Seeing as how close the batteries sit to the IC cutout (I labeled it wrong in the pic, not a uC) (see image below), there could be corrosion on the chip pins. The display could have also been affected by something. The traces are underneath, never hurts to take a look. There's a good possibility something 'shit the bed', leaky caps? dead chips? cooked resistors?, dirty pots?, hosed display?, lose wire?

Spoiler

 

[YoFavRussian]

16 hours ago, Calidus said:

So after taking it apart I see the corrosion went further along the same contacts that was hidden by the plastic so I cleaned those up. (although the cleaning left marks of its own) I couldn't see anymore damage or anything out of place but couldn't look under the board as its firmly in place and I didn't want to break it with unnecessary force.

 

Here's a link to some photos I took below, I'm still waiting on it to dry before trying it again.

 

https://imgur.com/a/8ahUjGP

Okay, so yeah, there is a chance that the corrosion leaked even further to the other side of the board. I would recommend doing what everyone else has said to do. New batteries, Alkaline batteries do operate at a higher voltage compared to batteries like NiMH. And trying to remove that plastic knob and inspect the other side of the board. Leaving corrosion go is very bad as it will just continue to eat away at the traces and will eventually come back up to the battery terminal.

[Calidus]

So on the other side where the battery terminal goes through the board, there's some marks on the solder and terminal. So probably has gone through the one one behind the screen. No traces that I can see so far is damaged thankfully, I have however noticed a witish coating where I cleaned the previous terminals, seems citric acid may of not been a good idea. (although was suggested online as a cheaper alternative to the professional cleaners)

 

I think I may need to buy something that was actually made for the job before I continue further, does anyone have any recommendations on any products to clean the contacts and such?

[KeyboardCowboy]

2 hours ago, Calidus said:

citric acid may of not been a good idea.

...well how bad was the corrosion? Citric acid is mainly used for dissolving rust (I had to look it up). I would shy away from using it on a pcb full strength. P.S. Acid and metal is not the best combo.

 

A better solution (Jacked from ifixit)

Spoiler

First remember that your batteries are alkaline not acidic. Alkalinity is just as corrosive as acidity but to clean it you will need the acidity. I use a 50/50 mix of vinegar and sterile water. It is okay to place the whole board in that solution. Use a small soft brush to gently scrub the residue of the board. Once it is properly cleaned, rinse it of with sterile water. Then clean the board with 90%+ isopropyl alcohol to displace all the water. Looking at the schematic, your GameBoy should work with just an AC adapter. If you post some images of your circuit board and the damage, I am sure we can give you a better idea on how to fix it.

I personally use distilled water followed by a good isopropyl rinse (for pcb cleaning in general).

 

I would get a wash bottle, and some anti-static brushes. Give your board a rinse down with the distilled water, agitate the surface of the pcb with your brush, rinse again, rinse with isopropyl, then let it dry (completely). This should help to remove any residual citric acid.

 

See what others have to say, I'm just one cowboy *pew pew*

[Calidus]

On 8/23/2019 at 12:54 AM, KeyboardCowboy said:

...well how bad was the corrosion? Citric acid is mainly used for dissolving rust (I had to look it up). I would shy away from using it on a pcb full strength. P.S. Acid and metal is not the best combo.

 

A better solution (Jacked from ifixit)

  Reveal hidden contents

First remember that your batteries are alkaline not acidic. Alkalinity is just as corrosive as acidity but to clean it you will need the acidity. I use a 50/50 mix of vinegar and sterile water. It is okay to place the whole board in that solution. Use a small soft brush to gently scrub the residue of the board. Once it is properly cleaned, rinse it of with sterile water. Then clean the board with 90%+ isopropyl alcohol to displace all the water. Looking at the schematic, your GameBoy should work with just an AC adapter. If you post some images of your circuit board and the damage, I am sure we can give you a better idea on how to fix it.

I personally use distilled water followed by a good isopropyl rinse (for pcb cleaning in general).

 

I would get a wash bottle, and some anti-static brushes. Give your board a rinse down with the distilled water, agitate the surface of the pcb with your brush, rinse again, rinse with isopropyl, then let it dry (completely). This should help to remove any residual citric acid.

 

See what others have to say, I'm just one cowboy *pew pew*

Yeah, I think I made the mistake of using pure citric acid without diluting, I'm going to grab some distilled water and some ESD brushes off amazon and do a proper clean when I have the time. (works been busy)

 

I'll add a reply once I've taken another go at it, might be next week though.