Tandy 1000HX display issue - any pointers?

[oracle_jedi]

Hoping one of the experts might recognize this, or have an opinion.

 

A Tandy 1000HX.  When in the 16 color graphic mode, some of the display is clearly not right.   What is supposed to be white comes off pink.   Green colors are not consistent.  

 

The Secret of Monkey Island shows that for some mode/colors it looks fine.  Leaderboard shows how the green is causing ghosting.  Two different Commodore 1084 monitors showing the same issue, and both monitors work fine with an Atari PC1/Amiga/ST etc.

 

Composite mode is better, and mono text looks fine.   I am guessing this might be a sign I need to recap the mother board?

 

Anyone seen this before?

 

 

 

 

[oracle_jedi]

And....  I answered my own question!

 

I needed to add 120Ohm resistors to the RGB lines when connecting to a 1084 monitor.   Looks so much better now!

 

 

[Geoff Oltmans]

Interesting... I haven't had a 1000HX in some time, but I used it with a Commodore 1080 monitor and never experienced this issue. Worked fine for me, but then again that was a Toshiba monitor instead of a Philips or Daewoo like the 1084.

[oracle_jedi]

An update on this:

 

I was wrong!

 

It wasn't the 120 Ohm resistors that fixed the problem at all.

 

In order to test my theory that I needed resistance, I cobbled together a spaghetti of cables that MacGyver himself would have been proud of, in the middle of which was a video cable for an Atari ST that did include the resistors.

 

Further testing revealed that it was actually the absence of pin 7 on the connector (CGA reserved, 1084 composite sync) that was chiefly responsible for the dramatically improved picture quality.  Switching the 1084 into RGBI mode made no difference here.  If Pin 7 was connected, I ended up with ghosted colors and a poor quality image.

 

So I rigged up a new cable connecting R, G, B, H, V, I and tying the two ground pins together on both ends (pins 1&2).

 

That gave me a nice stable picture in glorious 8 colors.  For some reason the intensity bit did not seem to work.  

 

Another round of head scratching and I found that not tying the ground pins together, but simply connecting Pin 1 (Tandy) to Pin 1 (Commodore 1084) and Pin 2 to Pin 2, resulted in a stable display in all 16 CGA/TGA colors.

 

Hope that helps anyone else looking to connect a Tandy 1000 to a Commodore 1084.