[J.B. Wood[_2_]]

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,
--
J. B. Wood e-mail:

[Peter W.]

A friend of mine brought over his ADT pushbutton panel the other day, reporting it "not working". It is fed from the back either by a 4.5V power-supply (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 large build-up of green salts concealed under the batteries.

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

Peter Wieck
Melrose Park, PA

[John Robertson]

On 2020/11/17 6:59 a.m., Peter W. wrote:
A friend of mine brought over his ADT pushbutton panel the other day, reporting it "not working". It is fed from the back either by a 4.5V power-supply (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 large build-up of green salts concealed under the batteries.

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

Peter Wieck
Melrose Park, PA


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 :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
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MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
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www.flippers.com
"Old pinballers never die, they just flip out."

[Peter W.]

https://encrypted-tbn0.gstatic.com/i...QfPCQ&usqp=CAU

I keep one of these back from my college days, together with various inserts 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 marl is non-conductive although the material removed may be.

Peter Wieck
Melrose Park,PA

[Jeff Liebermann]

On Tue, 17 Nov 2020 09:10:11 -0500, "J.B. Wood"
wrote:

Has anyone
had a similar problem? Thanks for your time and comment. Sincerely,

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:
http://www.learnbydestroying.com/jeffl/crud/Kirkland-AAA-leak.jpg

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:
https://www.energizer.com/batteries/energizer-ultimate-lithium-batteries
For the D cell, just use a 1x AA to D cell adapter:
https://www.ebay.com/itm/353243622867

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.



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