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New toy: Tandy DMP 132 (26-2814) printer
August 03rd, 2023
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Picked up a new toy from a local e-waste recycler: A Tandy DMP 132
(catalogue number 26-2814), Circa 1987. They let me have it after we
plugged it up and determined that it doesn't even idle properly; all of
the status LEDs light up, but it should only have the power LED lit if
all is well, perhaps the alert LED should blink if there's no paper too.

When I got home I popped it open and determined that it contains an NEC
D7810HCW CPU with a 14.7 MHz clock crystal. I looked up the datasheet
for the CPU and determined that it is normally clocked at 12 MHz, and
contains 256 bytes [sic] of RAM and 4K of ROM. (note: ROM and RAM are
both externally expandable, but Tandy definitely is using only the base
amount of RAM on this printer)
The CPU is a nominally 5 volt CPU, the onboard RAM fails to function if
it dips down to 3.2 volts.

Armed with that little bit of information, I started probing a few spots
on the mainboard that conveniently had voltage labels and determined
the +5 VDC rail of the PSU is only putting out around 2 VDC. 😱
No wonder it doesn't work!

I found a SAMS Photofact which shows that the other rails on the PSU are
+24, +12 and -12; not terribly unusual for a printer of this vintage.
But there are not many quadruple output power supplies these days either
that are not expensive. I couldn't find a specification for the number
of amps each rail is supposed to output either, but the primary side of
the existing power supply surely doesn't draw more than 2 amps or about
20 watts according to the sticker on the bottom of the printer and the
manual I have been able to find online. I have decided to go with a
Mean-Well RQ-65D as it matches the input amperage and has the required
voltages on its output rails.

For input, the printer has a centronics port which I will not be using,
and an RS-232C port with a 4-pin DIN connector of some type, it is using
only the common ground, transmitted data, and data terminal ready parts
of RS-232. From what I can tell the port expects the 8-N-2 configuration
at a baud rate of 600, 1200, or 2400.

Will update again once I have the replacement power supply...

=> Owner's manual | CPU datasheet | SAMS Computerfacts Technical Service Data | Potential PSU datasheet

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Comments have been left on this post:

I have a DMP 107 next to me now. Connected with a DIY PC-compatible LPT 
cable it even works in modern Linux, inc gfx ~freet
Posted Sat Aug  5 00:58:53 UTC 2023 by 1.152.108.92
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