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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.

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
The actual factory memory backup battery is a CR2032 that has welded-on solder tabs, is wrapped in clear plastic and then a yellow heat-shrink rim to lock the plastic in place.

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

A few relevant notes from the editor 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). I used to have very bad luck replacing coin cells (the new ones would be dead in anything from a month to six months). A trick I learned while working at NASA-JPL in the 1970s 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. 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 - een more so than skin oil. 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.