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  Replacing the Memory Backup Coin Cell in the Radio Shack™ HTX-202 and HTX-404 Handheld Radios
by Richard Luts KD4SEV
Instructional article by Craig LaBarge, WB3GCK
Edited and HTML'd by Mike Morris WA6ILQ

The article below and the PDF instruction file is oriented towards the HTX-202 and completely ignores the UHF HTX-404. Be assured the procedure is absolutely identical.

From an email received by Repeater-Builder from Richard Luts KD4SEV:
Recently my Yaesu VX-7 suffered battery failure, and I was loath to be without an HT on a daily basis and being of little cash, I looked to resurrect my HTX-202. The dreaded ERR-1 memory error had caused me to put it up on the back shelf of the shack many years ago, as well as the need for new batteries. After looking around on the internet (Google is our friend) I found great detailed instructions on replacing the 3-volt lithium cell by Craig LaBarge, WB3GCK. A short time later I had a socket and a new coin cell in hand, and after a short session on the workbench I was back in business.

Now to deal with the main battery issue:

After careful consideration I chose the IC-8 AA pack from Batteries America. This is a shell that holds eight AA batteries in any configuration, NiCad, Ni-MH, Alkaline, Lithium, and Carbon-Zinc. Additionally the IC-8 can recharge the rechargeable batteries via the standard BC-35 drop-in charger as well as a built in coaxial power (charge) jack.

I am back in business and with the addition of eight 2500 mAh AA rechargrable batteries, I have a great brick that runs for over three days between charging, puts out the full 5 Watts of VHF goodness and if a cell dies, it takes no time at all to replace them. For public service events or ARES, the longer run time, and heavier charge density makes this radio vastly superior to my newer FT-50-RD, and VX-7. And if I'm out in the boonies and run out of charge I can pop in 8 AA penlight batteries and I'm back on the air.
Great stuff

Richard Luts KD4SEV

Click here for a step-by-step procedure by Craig LaBarge, WB3GCK     233 KB PDF file

A web page (with photos) on the same topic by the same author

A few relevant notes from Mike Morris WA6ILQ:

1) As mentioned above the Batteries America IC-8 pack holds eight AA 
cells.  DO NOT mix alkaline, nicad or nimh types. The chemistry of a 
battery pack has a distinct effect on the voltage produced. 
Nickel-Cadmium (NiCd) batteries deliver 1.2V per cell when fully charged, 
Nickel Metal Hydride (NiMH) deliver 1.25V per cell. Each 8 cell  battery 
pack produces 9.6V from the NiCds and 10V from the NiMHs. The alkaline 
cells produce 1.5V each so 8 cells yield 12V.

2) If you are going to store the radio for a while (like in your "go-bag") 
remove the cells from the battery holder, and keep them in a zip-lock bag. 
If one or more cells leak the acid is not going to destroy your battery 
pack. Note the purchase date of the cells on the zip-lock bag with a 
Sharpie pen. You can refrigerate the batteries (do NOT freeze them) to 
extend the shelf life, just let them warm up overnight before use.

3) Ideally you would have two holders and two sets of cells. The middle 
of a disaster operation (even if it is just a weekly roll call net) is 
the time to swap packs, not to swap cells in a pack.

4) The current drain by the memory chip from the coin cell is measured 
in hundredths of a microamp - which is why the cell the size of a quarter 
can last ten to fifteen years.  The resistance of a fingerprint - a 
very thin film of skin oil - is many times lower than the load 
resistance of the memory chip. If I have the physical clearance I always 
replace a soldered in cell with a socket.  One acquaintance had a piece of 
equipment with a soldered-in memory backup battery - he salvaged a coin cell 
holder from an old computer motherboard that he soldered to a piece of perf 
board and mounted to the inside of the equipment case (i.e. he used a cell 
holder and some twisted pair wire to relocate the call to a more convenient 
area to make future replacement easier).

A trick I learned while working at NASA-JPL is to handle the coil cell itself either wearing very clean rubber or latex gloves or to be VERY careful and not bridge the insulating ring between the positive and negative terminals with your finger or thumb, which leaves behind a fingerprint on the cell - a current leakage path. I used to have very bad luck replacing coin cells (the new ones would be dead in anything from a month to six months). My success rate has gone way up since I started being very careful to: a) Avoid leaving flux on the board, especially under the socket (i.e. between the coin cell holder and the PC board) where you can't see it. Flux is mildly conductive. b) Clean the coin cell holder itself after installation. Use a cleaner that does not leave residue. c) Be careful to not leave a flux track (a discharge path) on the back side of the board as you solder the coin cell holder in place. d) Do not bridge the insulting ring as the cell is soldered into the board (in the case of soldered in cells) or... e) Do not bridge the insulating ring as the new cell is slid into the coin cell holder. First strip the board of the old cell, then clean the area where the cell used to be, then solder in the new coin cell holder, then clean the holder itself (i.e. where the cell will go), and the solder pad areas, then don the rubber glove before opening the blister-pack containing the coin cell... Be careful as you put the glove on to keep the finger pad areas clean - no sense in adding skin oil on the areas of the glove that you are trying to keep clean! (or clean the glove after it's on)

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This page initially created 01-Jun-2009.

Article text and photos are copyright © 2009 by Craig LaBarge, WB3GCK.
Radio Shack, Realistic, Archer and probably others are legal trademarks / service marks of Tandy Corp and no infringement is intended.

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.