TI-H: PC Board traces

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TI-H: PC Board traces

I heard somebody asking about broken chip leads or PC board traces,
so here's what I learned from breaking, and successively fixing,
my calculator in the process of installing the turbo modification.
(PS DO IT!!! If you have the steady hand [which I don't], you should
do fine and it is *great*!)


All info for regular (non-CE) version.


The big chip on the left of the board is U4. The upper left pin
on this chip is pin number 41, I believe (it's labelled on the 85
main board). I assume that pin numbering goes counterclockwise in the
following (which may or may not be true, AFAIK). Thus all of the
following pins are on the left side of U4 below pin 41:


                             No connection -- |48
                **    BIG PC board trace      |
                 **************************** |49
                                       |      |    U4
                                       C9---- |50
                                       |      |
                                       R11----|51
C9 is the infamous 33pF timing capacitor, placed between pins 50
and 51. R11 is a 2.7 KOhm resistor which forms the other half of
the timing circuit. It is physically located just to the left of
C9. The big PC board trace goes over to the
display board. If you break the trace, you can solder a jumper
from pin 50 to an exposed copper spot on the trace just below
the circuit board.


A summary of what I wound up doing:
-Repair big trace
-Install a 2.2K and a 470ohm resistor in series (2.67K,
  replaces R11). Solder between pins 50 and 51.
-Solder one lead of switch to pin 50, other lead to a 33pF cap,
 and other lead of capacitor to the same point on the big trace
 where I had soldered the jumper from pin 49.
-Lotsa electrical tape


This is the reason I don't believe in the feasability of installing
a radio link inside the calc--I could barely get my calculator
shut!


At any rate, if your calc won't turn on, at least check out the
above connections before you shell out another hundred bucks.


--Jon, N9RUJ
jnieho38@calvin.edu              www.calvin.edu/~jnieho38
"I don't believe in gun control. I just fire wildly."-A. Schlair