Franc Zabkar wrote:
**The tablet came sans power supply. Based on the specs I picked up a 12volt,
1 amp supply. Manual says mfr's p.s. must be used or wtty is void. Is this a
possible issue?
Page 15 of the manual states that the tablet needs a 12V ***AC*** 1A
power supply. Instead you have provided a 12V ***DC*** 1A power pack.
Oye-- How dumb is that!!! So this is just a step-down transformer!! I thought
all the bricks were AC to DC. Do you think using 12v DC could have hurt the
board? Or that it could be the source of my problems??? Not many of these
supplies out there. Did find one with a 3' cord though that I will pick up.
**I note there are what appear to be contact tabs (labeled +12v AC, -12v,
+12v, +5v, DIG GND, DIG GND) at the bottom right (plan view). Are these for
test fixture powering?
Maybe. Measure them with a multimeter. I'm betting that the +12VAC
(???) and -12V rails will be missing. The -12V is required by the
tablet's serial port, and possibly by the analogue circuitry for the
digitizing surface, and for various op-amps.
Didn't get any current when board was plugged into my !@$#$@% power supply--
perhaps AC will make a difference.
I'm betting that the 2-tones error indicates a problem with the
analogue circuitry.
I also saw at p. 40 of the UG that there are THREE MG3TEST diagnostic tests:
RAM, X-axis, and Y-axis--perhaps corresponding to the 3 tones??? Or not! If
so tho, might suggest Y-axis circuitry.
If you get your MG3 working, I would still run the MG3TEST. I've seen
lots of tablets with dead spots on the surface, usually caused by dry
solder joints, or bad driver chips (yours appears to use the ULN2003
chips).
One ULN2003...along with six UDN2595-A dips which I think are drivers.
BTW, if you ever need any spare ICs, keep me in mind. I have a lot of
chips of that era ... somewhere. You'll just need to pay for postage
from Australia. I also have a new unused 4-button Summagraphics puck,
but that cost me money.
Will keep all that in mind!
Thanks!
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