"powerseed" u43512@uwe writes:

This equipment (a Microgrid III 36" x 48" graphics digitizing tablet ca 1992)
is a tad esoteric at this point..no factory service, tech manual available,
etc. I'm a student trying to resurrect this old bird for my GIS classes.

Serial interfacing software (Vtablet) is available for connecting this to my
XP Pro Compaq laptop. I bought a serial port to USB adapter (Keyspan) for my
MGIII which self-installed at COM5. Since the COM1 port was occupied, I reset
the serial Keyspan adapter via the Windows Device Manager to COM2 and set
Vtablet to COM2 as well. Following recommended start-up procedure (Microgrid
tablet on, then boot) I am unable to elicit any puck output (screen cursor
movement in response to moving the puck on the tablet) which is also
confirmed as zero port interrupts on the software's Status tab.

I am now concerned that the tablet controller is misbehaving . I also note
that the Microgrid start-up only produces two tones instead of the €œall okay€�
three tone self-diagnostic (don't know the implication of the missing tone).

The unit has a removable 8" x 13" controller board and I was wondering if
anyone out there could direct me to an circuit troubleshooter who could look
it over and hopefully repair???

First things to do would be to confirm

(1) that the serial port adapter has installed properly. I've used this or
a similar unit and the installation can be buggy especially when switching
to a different port. Either connect it to another PC with a known working
seerial port or select in a terminal emulator that is known to work with
COM5 and see if loopback works.

(2) that the tablet is actually outputting something on the serial port.
Make sure it either doesn't need any hand-shake signals (CTS, RTS, etc.)
or that they are set properly.

(3) that the cable has pins 2 and 3 swapped, or not swapped as required.
When connected correctly, there should probably be a negative voltage
on both pins 2 and 3 with respect to pin 5. If incorrect, then
there will be a voltage on only one of those pins.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.