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conductive Path on printed circuit board?

Hello,

I had been having a recurring problem with a model WV-38A RCA VOM that I built from a kit way back in the day. For resistance measurements it uses 4 AA cells and 1 D cell. Over the last couple of years sometimes it worked fine and at other times the meter wouldn't budge, regardless if voltage, current or resistance was to be measured. I couldn't find anything amiss either- no blown fuse, broken circuit board traces or faulty or oxidized wafer switch contacts. I spotted some green (apparently conducting) material on a circuit board trace near a battery holder that had also migrated to other parts of the board. I think the material came from a leaky battery. I cleaned it off with rubbing alcohol and the VOM once again seems to be working reliably. Has anyone had a similar problem? Thanks for your time and comment. Sincerely,

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J. B. Wood	            e-mail: arl_123234@hotmail.com
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J.B. Wood
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A friend of mine brought over his ADT pushbutton panel the other day, repor ting it "not working". It is fed from the back either by a 4.5V power-suppl y (wall-wart) or 3 x AA batteries in a pocket between the body and the wall

-mount. Two things had happened: a) The little SMT power-jack had pulled away on two of the four tabs. That was a quick fix. b) In some previous time, one of the batteries had leaked and there was a l arge build-up of green salts concealed under the batteries.

He had installed new batteries, but the salts had bridged connections, caus ing them to short. I used an electric drafting eraser and dental picks to g et all the corrosion out and soldered over the traces. It works. NOTE: Those salts are deliquescent - meaning that they attract water out o f the air - so no surprise on the migration.

Peter Wieck Melrose Park, PA

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Peter W.

Leaky batteries can be a big problem. Of course we forget to keep checking them. Every brand will leak, but the problem is finding out which is worse. Where I worked before I retired we got Duracell from a local hardware store. I really think they were a knocked off brand ! I have used Duracell the last couple of years and have been happy with them although most brands are within price range and work just as well. They die in my remotes well before any leakage can happen.

KenW

Reply to
KenW

White vinegar 50:50 with water is a good neutralizer for the alkaline salts. Foams up then washes off...got that tip back in the late 80s or early 90s from Duracell (or Eveready) mail in tech support. Have long since lost the letter...

CLR also works, it too is a mild base.

John :-#)#

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John Robertson

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I keep one of these back from my college days, together with various insert s from "kiss a soap bubble" to "peel chrome from a trailer-hitch". They do an amazing job of cleaning everything from contacts to dirty plastic. The m arl is non-conductive although the material removed may be.

Peter Wieck Melrose Park,PA

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Peter W.

Oh yes, many times. I have a fairly large number of alkaline battery powered devices. Around 1995, alkaline batteries were reformulated to remove lead from the "stabilizer" that kept the batteries from leaking. Since then, 5 to 10 years is about the average shelf life before they begin leaking. These died in the box after about 8 years:

Instead of alkaline, try substituting a lithium (not a lithium ion) cell. These are more expensive, have a much longer shelf life, and don't leak. The AA cells, this should work with 20 year life: For the D cell, just use a 1x AA to D cell adapter:

The down sides of using lithium is the cost and that they are not rechargeable. For a VOM/DVM, a few extra dollars over a 20 year operating life is negligible. Just do it.

You can also substitute LiIon or NiMH cells, but these require some compromises. The LiIon cell is a nominal 3.6V with a maximum of 4V. Plug 4x 14500 LiIon cells into a device made for 4x 14500 alkaline cells and your RCA VOM will blow up. You can try running the VOM on

2x 14500 LiIon cells if the design will handle running on 8V instead of 6V. Or, you can install some series diodes in the VOM to drop the voltage to 6V. For the D cell, I wouldn't bother as the required 2.5v drop will be a major waste of power.

You can also use NiMH cells, which are approximately the correct voltage. The problem here is the cheap cells have a high self discharge rate and will need to be recharged quite often. Fortunately, there are plenty of LSD (low self discharge) NiMH cells available, such as Eneloop. For the D cell, use the previously mentioned AA to D adapter.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
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Jeff Liebermann

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