Thanks Brian. Understood. I'm going to build-up a connector as you suggest. In the meantime, after a closer look, I am seeing that some pins in the male header that connects to the T200 bus are indented -- not bent but not long enough to ensure a connection with the female system bus connector on the T200. I'm going to see if I can pull those particular pins out a bit further and try again. Also, the construction of the adapter appears to use very short reinforced jumper wires with pre-soldered pins on each end (kind of like what is pictured below), inserted directly into the headers. This means it should be relatively easy to pull the wires out and reorient them as you proposed. Tom
[image: image.png] On Wed, Sep 25, 2024 at 9:47 PM Brian K. White <[email protected]> wrote: > 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 > >
