Simpson 260-3

[Fisher77]

Picked this up at a yard sale for a couple of bucks. Tore it down today, and it is pretty crusty/corroded. Nice leaky alkaline batts been in there for no telling how many years. Corroded traces, wirewound resistors, and pots. The wirewound resistors still ohm out to spec, but the legs are corroded. The pot in the pic with the corrosion on top I have not checked, but the zero ohms pot is not ohming out correctly. I assume it has corroded internally since it is right where all the alkaline leakage is.  Any way to salvage this, or should I put it back together for a dust collector on a shelf? What would be the best approach for removing the corrosion, and crust?

Thanks

[retiredcaps]

What would be the best approach for removing the corrosion, and crust?

Not an expert, but this worked for me

https://www.eevblog.com/forum/chat/fluke-187-corroded-battery-terminals-how-to-clean/

After getting rid of the corrosion, an IPA bath of the entire pcb with a toothbrush should get rid of the contamination.  Let it dry thoroughly and then retest.

[Fisher77]

Thanks retiredcaps. This may be a stupid question, but can I the board in vinegar like you did the battery contacts, then neutralize with backing soda, then soak in IPA with the components still on the board, or do I need to remove them first?

[retiredcaps]

Let me detail what I would.

1) Mix vinegar/baking soda in a small cup.  Dip toothbrush into cup and scrub away the battery corrosion. Repeat as necessary.

2) Put IPA into a small cup.  Dip toothbrush into cup and gently scrub entire pcb. Repeat as necessary.

3) It is possible to dunk/immerse the entire pcb board into IPA depending on the components.  Post a clear focused picture of the pcb, both sides, so we can see.  I have immersed Fluke multimeter pcb entirely into IPA without any problems.

[Fisher77]

Here are pics of the board.

[retiredcaps]

Everything on the that board looks "dunkable" to me in IPA.  Dunk and give it a good toothbrush scrub.

Just make sure to dry everything thoroughly.  A small computer fan blowing on it at various angles overnight will help.

PS. I would wait 24 hours to see what other members have to say before following my suggestions.  I have had success with IPA, along with others, but your mileage may vary.

[Fisher77]

Thanks retiredcaps, I will give others time to chime in. I dont think it would hurt to dunk it either. I will clean the case meanwhile, I know I cant mess it up.

[retiredcaps]

I will clean the case meanwhile, I know I cant mess it up.

One person over at badcaps.net got a great deal on a Fluke 77 IV ($30 USD iirc) and used IPA to clean the outside.  In process, he rubbed off all the silk screen symbols.

[Fisher77]

Dang, thats a bummer. I am going to just use good ole soap and water on this bakelite case. Surely that will not take the symbols off.

[retiredcaps]

Dang, thats a bummer. I am going to just use good ole soap and water on this bakelite case. Surely that will not take the symbols off.

Soap and water should be fine.

[mzacharias]

Dang, thats a bummer. I am going to just use good ole soap and water on this bakelite case. Surely that will not take the symbols off.

Yikes. Glad my 87's,  28II and 289 etc didn't suffer this. Cleaned them many times with 91% isopropyl. Never a problem (thank God).

[Fisher77]

Ok, I followed your advise retiredcaps. Did a little scrubbing with vinegar and a toothbrush, followed by a mixture of backing soda and water to neutralize the acid in the vinegar. Wrinsed with clean water, then dipped in IPA and scrubbed a little more with a toothbrush. I then sit it out in the hot West Texas sun for about 8 hours so it should be dry as a powder house fart now. As for the "0" adjust pot, I pulled it from the board, soaked it in vinegar, then baking soda, wrinsed, then IPA. Sit it out in the same blistering hot sun. It now reads correctly on a DMM.  The only damage I see is that it removed some of the resistor and diode numbers. No worries there, I have a full schematic, and parts list. Other than that everything is good.

Next delima is the wirewound resitors. The sheathing on the wire is green so i would assume that the wire inside the sheathing is green. They all ohm out to spec, but I am betting in the long run they will fail. Any idea where I can find them?  Values are: 0.452 ohms, 2 ohms, 11.2 ohms, and 22.5 ohms.

[Fisher77]

Okay, I have been looking at wirewound resistors. I cant find a 0.452. I can series together 2 different combinations to get either .420, or .460.

What would be the best way to go?

[retiredcaps]

What would be the best way to go?

If you can't find the exact resistors, putting resistors in parallel or series is your option.  Which way? I would probably lean towards .460 myself.

[Fisher77]

What would be the best way to go?

If you can't find the exact resistors, putting resistors in parallel or series is your option.  Which way? I would probably lean towards .460 myself.

 
Let me ask you a question retiredcaps. I am still learning here.  Is it possible to parallel two resistors say a .8+.61 to get .35ohms, then series the two parallel resistors with a .1 to get .45ohms? Would that work?

[retiredcaps]

Is it possible to parallel two resistors say a .8+.61 to get .35ohms, then series the two parallel resistors with a .1 to get .45ohms? Would that work?

Yes.  However, space might limit you how much can do.

If this were my meter, close enough is good enough.

[mzacharias]

If you can't find the exact resistors, putting resistors in parallel or series is your option.  Which way? I would probably lean towards .460 myself.
[/quote]


I have found that on analog meters the resistor values are not 100% critical. For example, just exactly how accurate does an Rx1 range need to be, really? If for example you are checking that a 10 ohm resistor is OK, does it really matter if the VOM appears to say 9 ohms or 11 ohms? The resistor you are testing is OK for all intents and purposes. If you really need accuracy, you need a decent digital meter anyway. (I realize the original poster may be limited in this respect due to economic issues)

[Fisher77]

Yes.  However, space might limit you how much can do.
If this were my meter, close enough is good enough.

If you can't find the exact resistors, putting resistors in parallel or series is your option.  Which way? I would probably lean towards .460 myself.

I have found that on analog meters the resistor values are not 100% critical. For example, just exactly how accurate does an Rx1 range need to be, really? If for example you are checking that a 10 ohm resistor is OK, does it really matter if the VOM appears to say 9 ohms or 11 ohms? The resistor you are testing is OK for all intents and purposes. If you really need accuracy, you need a decent digital meter anyway. (I realize the original poster may be limited in this respect due to economic issues)

Thanks for the help guys. As close as I can get it will just have to be good enough. I would like it to be as close to accurate as possible, but will not be depending on this meter for accurate measurements. I have a couple of DMM's for that purpose. I appreciate all the help. Going to get the resistors ordered, and put in. I will post back when I get it back together, unless I run into another problem that I need help with, which will prolly be the case.

[Fisher77]

Ok I got some time to replace the resistors, and the meter now has life. Now for the next problem. Volts is working just fine. Resistance is not. When I switch to Rx10,000 it pegs the meter out, and I cannot zero it. When I turn the zero pot, the needle moves, but never gets to zero. On Rx100, and Rx1 the meter does not do a thing. I have checked all the resistors on the board, checked the zero Pot, and all are within spec. What else can I check?

Thanks for any help.

Update: Just sitting with the leads shorted together the needle in fluctuating.

[retiredcaps]

What else can I check?

Check range switch for dirt/debris, cold/bad solder joints, etc?

[Fisher77]

Thanks retiredcaps. Finally had a chance to mess with it again. I checked the range switches. I have sprayed them with contact cleaner, blown them out with air, reflowed all the solder joints, and dabbed a little wd40 on the switch boards so if they had dried out and shrank(tip I found on youtube), dont know if it is a legit tip or not . I can say the boards soaked it all up. I have tried everything I know to clean those switch contacts short of desoldering them from the board. I am still having the same problems. I have now seen that when I turn the zero pot, that the needle jumps all over the place on Rx10,000. The needle still moves all the way to the left on Rx1, and Rx100 and turning the zero pot does nothing on those 2 settings. I ohmed it out before, and it was in spec. But now it seems to be loosing contact. I have sprayed it with contact cleaner, and blown it out as well. Also sprayed it with contact cleaner with lubricant in it, no change.  Possible bad pot? Or is there something else that can cause it to act like this?

[mzacharias]

Think of your ohms circuit as a closed loop with resistors and batteries in there. Remove the batteries, short the battery terminals together to complete the string without batteries, connect a second ohmmeter to the input jack terminals of the 260. The second meter should now be reading the total circuit resistance. Push and poke the various connections and switches etc til you find the bad one. Alternatively, with the batteries inserted in the Simpson, put a resistor across the leads, maybe about 10K for the 10K range, and put a DC coupled scope across the resistor, maybe on about a 1 or 2 volt per division setting. You will see the  flat line on the scope jumping around whenever the internal connection flakes out. Looks like a noisy signal. I have used variations of these techniques to troubleshoot many analog type VOM's.

[Fisher77]

Thanks mzacharias, that meter to meter test did the trick. Found 3 resistors that I could mash down on with my finger, and the second meter would read resistance, let the pressure off the resistors, and the second meter went OL. I put the batts back in pressed on the 3 resistors in question and the needle would move to the right and I could zero it out. I reflowed the joints on resistors R1, R2, and R4. I think I may reflow all the joints on the board to avoid any problems later on. The picture shows the resistors I had to reflow in case anyone in the future has trouble with theirs.