Wednesday, October 20, 2010

Memory fix

Six months ago I bought an old Kenwood TH-205 on eBay for spares or repair. I got it working, managed to find a new replacement NiCad battery pack for it and built a drop-in charger for it for a total cost of well under £20. The backup battery had died so the memories didn't work and the radio wouldn't even remember the frequency it was last used on, but I was pleased just to have got it working and I was afraid the replacement would be an expensive part the cost of which couldn't be justified.

Today I decided to have a look and see if the backup battery could be replaced. I wasn't sure where the backup battery was, but I guessed it might be hidden under a foam pad in the centre of the circuit board. I had a peek and was pleased to find that it was a CR2032 3V lithium button cell. However it wasn't your regular CR2032 cell that you can buy in stores, but one with solder tags spot welded to each side.

I looked on eBay, but although this turned up zillions of sellers of the regular cells at prices from five for a pound, no-one had the version with solder tags. I looked to see if I could fit a cell holder into the radio but the PCB mount one I had was quite a bit thicker than the cell itself and there was insufficient space for it.

I tried a Google search and Digikey had a CR2032 with solder tags for £1.17 a time, but there was a £12 shipping charge which made it uneconomic. The cost of the repair needed to be proportionate to what I paid for the radio.

So I decided to try taping wires to a regular CR2032 cell. I doubt that I could solder to it, and that probably isn't a good idea anyway. I had a CR2032 which came in a kit I purchased recently but haven't started to build yet. It was new and sealed in its packing so I thought I would use that. It was a good job I decided to check the voltage after taping the wires to it, in order to verify they were making good contact, because it was as dead as a dodo! Even the one I took out of the radio showed more signs of life, as it acts as a capacitor and charges up a little bit when the battery power is turned on.

So it's back to eBay to order a couple of replacement cells, one for the Kenwood and one for the kit I haven't yet built.

5 comments:

Big Gun DXer said...

Julian,
you can de-solder (de-weld?) the tabs off of the dead one and solder them onto a shiny new generic CR2032. I just did it recently to resurrect an old HT. Helps to have a 200W soldering gun. Just be careful not to overheat the battery. Google memory battery replacement for HTX-202. There's a video online showing how to do it for that rig.

Julian said...

Thanks for the idea. I did peel the tabs off the old battery. Not sure how far I'd get with my little pistol soldering iron though.

IW1AYD said...

Hello Julian.
I have successfully tried to overcome the same problem you had.
I soldered two wires with a 50W iron solder to a CR2032 several times. A lot of portable PCs have those batteries for the BIOS CMOS RAM. Usually those portables have an insulated dongle with inside a CR2032 as you noted with those slim terminal spot welded. Then to get out of the insulated dongle there are two wire more conventionally soldered to the above terminals. At the end of the two insulated wires there are minuscules two way connectors. It's a must to save this grain.
So applying the right patience and some not so brute force I use the same terminals, the flat terminals, the wires and the grain connector.
Then I grab a small dish those for coffee cups are excellent and star my solder-cooking activities. Well there is the need a water film on the bottom of the dish. Firs of all I clean the surface of the battery, a well hot solder and some of the ancient tin lead solder. I will deposit a film of this last on the two battery surfaces. Obviously having a well dry battery surface, so dry it when needed. Be fast, but firm, the water film will dissipate a lot of excess temperature.
Then have also the flat leads recovered from the gone CR2032 refreshed with some tin lead soldering on it. Be careful not to make a blob. Now put again the battery onto the dish and having the soldering iron and the flat salvaged lead onto the battery surface you will hate you job done. Do it two times, HI, taking care to dry the battery with a cloth as before.
Quick and dirty. I have done it a handful times. I have done it a handful of times. When in needs it works.

I would not tell you that usually I have more than just one CR2032 on hands, just in case you know. But no one was fried or severely injured since now. Also the dishes went out of this pretty well each time.

73 de iw1ayd Salvo

Steve GW7AAV said...

I have soldered wire to a CR2032 several times without problems. Last time I used my gun type soldering iron that I purchased for peanuts at Lidl supermarket.

The danger is they can explode if overheated so I made sure that the iron was well hot and the wires tinned before I touched the battery. I also let the cell cool between soldering sides. I put a couple of wraps of insulation tape around to prevent shorting as the cell can move inside the rigs case, which does not happen with the tabbed cell.

Alex Hill said...

Not sure if this (http://www.strikalite.co.uk/viewproduct.asp?from=sresults.asp&prodid=722&catid=11&cat=Lithium) is what you are after.

Cheaper if it is