G8MNY  > TECH     20.06.25 22:15z 68 Lines 2546 Bytes #190 (0) @ WW
BID : 35149_GB7CIP
Subj: Pac-Comm Tiny2 Battery Tale
Path: ED1ZAC<ED1ZAC<GB7CIP
Sent: 250620/2202Z @:GB7CIP.#32.GBR.EURO #:35149 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                                         (New Jan 08)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

I have been looking at the disastrous results of adding external backup
battery connection to a tiny2, as the small rare soldered in Li battery had
died.
The external batteries outside the metal case had been wired from the anode of
low voltage drop D5 to JPB 2 battery 1k earth jumper link.
          _ _ _ _ _ _ _ _ _ _ _ _ _ 
     D5  |                         |
   ÚÄ´<ÃÄÄÄÄÄÄÄÄ¿+3.6V         External
   ³           _³_            Replacement
   ÃÄ´<ÃÄoVCC   Ü Li           2x AA in
   ³ D4         ³ battery       Holder
   ³          1 o                  |
   ³      JPB 2 oÄ¿- - - - - - - - Ù
   ³          3 o ³
 ÄÄÁÂÄÄÄÄÄÄÄÄÄÄÄÁÄ)ÄÄÂÄÄÄoVBB to Ram Memory
    ³+            ³  ÀÄÄÄoBACKUP to IC U4 
1u ===            1k
    ÁÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄ0V

As you see from the circuit there is very little other than the 1uF protecting
the static sensitive memory IC from external electrical shock (static & HF).
The Li battery current limiting 1k earth resistor left in the external battery
system only making matters worse!

THE DAMAGE
In the end the TNC packed up with a blown up memory 62256 IC  & a Z80 S10/0 IC
Which handles the data bus to the memory & Z80 CPU. This was found by swapping
ICs to another TINY2, luckily all in sockets. The logic IC U4 a 78HC132 took
the Zapp OK!

MY SOLUTION
After replacing the ICs, I unsoldered the Li battery & wired the battery
connections to 2x AAA Alkaline cells (soldered to batts with special solder or
file ends) all tapped up (parcel tape) to provide insulation & some battery
leakage protection to the PCB & double side taped the bundle to the PCB where
the 82C88 IC hole space is.
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³12V         (~~~~~~~~)   DD    SW ³
³            ( 2x AAA )   45 [Li]  ³
³RIG          ~~~~~~~~             ³
³DIN        ÚÄÄÄ¿ ÚÄÄÄ¿ÚÄÄÄ¿ÚÄÄÄ¿ L³
³sw         ³   ³ ³   ³³EP ³³RAM³  ³
³           ³Z80³ ³Z80³³ROM³³MEM³ E³
³           ³S10³ ³CPU³³   ³³   ³  ³
³2          ³   ³ ³   ³ÀÄÄÄÙÀÄÄÄÙ D³
³3          ÀÄÄÄÙ ÀÄÄÄÙ            ³
³2                                S³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
I expect the 2 AAAs should last as long as the original Li?


I hope this tale stops anyone else from zapping their TNC.


P.S. don't forget to backup your TNC EPROM if you can, as EPROMS only have a 7
year G'tee image lifetime!  


Why Don't U send an interesting bul?

73 de John G8MNY @ GB7CIP


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