Yeah, looking closer at the pic, I think you've double twisted.
It looks like 2 male solder pin headers back to back, so far so good.
And it looks like one connector is polarity-notch-up (in the 200),
and one down (on the cable, you can see the 3 little flux wash bumps
facing up), also so far so good.
And it looks like the wires are crossing up to down/down to up. That's
the error.
Just soldering the 2 connectors back to back straight through (as long
as you flip one connector over) already accomplishes the "twist".
You want the polarity keys opposite each other. Another way to say it is
you want the pin-1 marks as close as they can get to each other. You
will see that, back-to-back, it's impossible to match up the triangles.
Instead, pin 1 can only go to pin 2 or pin 39.
By comparison, Simply crimping 2 male connectors onto a cable normally
to make a normal male-male cable will NOT work. That would actually
preserve the 1:1 pin numbers. (Also a crimp-on male connector cannot fit
into the opening in a 200 anyway unless you cut the opening wider. Only
the solder-type fits.)
https://github.com/bkw777/TRS-80_Disk_Video_Interface_Cable
https://photos.app.goo.gl/3TmJLMhK1WJ23mr4A
You don't really need the little pcb.
Mystery solved I think!
--
bkw
On 9/25/24 19:46, Tom Blum wrote:
Hello,
I'm looking for any thoughts about potential faults that could explain
the following.
* T200 (that has been thoroughly inspected inside/output) powers-up and
is functional when not connected to DVI. Also powers-up and functions
with system interface cable attached to T200 as long as cable is not
connected to DVI. No optional ROMS are installed. Available memory at
power-up is 19K+
* Disk/Video Interface operates to spec when not connected to T200. DVI
boot sequence is nominal. Successfully loads ver 1.00.00.200 of disk
basic and displays confirmation of such on composite monitor.
Successfully boots with system interface cable attached to DVI and T200
_as long as T200 is not powered on._
* When T200 is connected via system bus to DVI (_with DVI powered off_),
T200 does not successfully power on. When the T200 power button is
pressed, the LCD screen goes solidly dark with no apparent other
functionality. It seems frozen. When DVI is subsequently powered on,
while T200 remains in frozen state, DVI sometimes succeeds and sometimes
fails to load software from the DVI disk. T200 can only be recovered by
cycling memory power switch on the underside of the T200 off-on.
A picture of the connector is shown below. It has been connected to the
T200 and DVI per illustrations from Arcade Shopper. As a cross-check,
I've ensured that pins on the connectors are intact and fully-inserted.
Intuition suggests that the issue resides with the T200 system bus, the
T200<->DVI cable and/or the "PPI" circuit of the DVI. Ironically, the
service manual for the DVI refers users to the T200 service manual if
there are issues with loading disk basic onto the T200. The T200
service manual/troubleshooting section does not address this problem.
Any thoughts on where to start? I do have a spare, working T200
motherboard. Swapping that in might help rule out issues on the T200 side.
Thanks, Tom
--
bkw
