[IRCA] PL-300WT/ G8 Watch Battery-- The Full Story

[D1028Gary@xxxxxxx]

Hello All,
 
Many new owners of the Grundig G8 (and its Tecsun PL-300WT clone) have  
been puzzled by the function of the circular watch-type battery located under  
the main circuit board, primarily due to the complete lack of documentation 
in  any of the G8 or PL-300WT manuals to describe its existence, or 
function. This  afternoon, a G8 was completely disassembled here to discover as much 
as  possible about this watch battery.
 
It is obvious that Tecsun never intended for this battery to be  replaced, 
since the both the positive and negative connections are very  tightly 
clamped on the battery, and the positive terminal is soldered to the  digital 
circuit board in an particularly awkward location. Despite its  appearance from 
the back side of the radio, the battery will not slide in and  out even if 
the top (negative) lead is completely pried off its top  (which is a pretty 
nasty job in itself, requiring repeated prying with a  very small jeweler's 
screwdriver). 
 
As far as function, this battery merely provides a backup for the clock  
setting when the other batteries are removed. When the round watch battery is  
disconnected, all the radio's functions will all operate normally as long 
as the  3 AA batteries are installed. The radio's memories are not affected 
by this  watch battery's removal, and my G8 retained all its preset memories 
throughout  the duration of the testing. The only issue that will occur if 
this  watch battery is removed (or dead) is that the clock will reset to 
12:00 if the  top AA battery is removed from its slot. Specifically, the top 
battery in  the three AA battery group is related to the clock setting, and you 
may  safely remove the two lower batteries and retain the clock setting, 
even if the  watch battery is removed. The watch battery's voltage was 
measured at 2.2  volts, and it is logical to assume that it simply takes the place 
of the top AA  battery (1.5v) to retain the clock setting, whenever that 
battery  is temporarily removed for replacement.
 
With such a limited function, this watch battery is certainly not a vital  
part of the radio's circuitry. Tecsun probably figured that the battery 
should  last for years with such a minor mission, and did not design an easy way 
for  removal or replacement. There is some lettering stamped on the 
battery's  side, such as "C.C/DCT/0C" and "0.22F," but no company name. Disassembly 
of  my G8 to obtain this information was far from routine, and is not  
recommended for hobbyists without serious technical experience. There was the  
fringe benefit of finally seeing the actual DSP chip in the G8, however-- a  
surprisingly small (1/8" square) component located quite close to the  
soldered-in positive terminal of the watch battery.
 
In summary, even though this watch battery has a very limited function, G8  
and PL-300WT owners can extend its life by promptly replacing the top AA 
battery  whenever the other two lower AA batteries are replaced. Such a 
practice will  probably extend its life well into the next decade.
 
73, Gary DeBock (in Puyallup, WA)
 
 
          
 
 
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