View Full Version : Tandy 1000 SL RGB output questions/issues

April 22nd, 2017, 11:04 AM
Hi everyone,

i just got myself a nice Tandy 1000 SL motherboard. I successfully modified an AT power supply so i could match the proper voltages with the connector. Whole issue with this is that i don't have any monitor capable of accepting RGBi signals. I do have a Turbo XT with CGA, which i have been using with a DAC with quite impressive results, the video quality is really amazing. The DAC just turns the TTL signals into 15Khz analog signal which i can use with a SCART TV, including a Sony PVM i got recently, some 15Khz VGA monitors or even using an upscaler, like the Gonbes 8220.

So i turn the PSU on and get no picture. So i decided to connect the audio output, and turns out the board was actually booting i heard a beep, but still no video. So i put a VGA card in and finally i get video. My conclusion is that this DAC that works so well with IBM CGA doesn't seem to work with Tandy video.

Could this be some DAC incompatibility with Tandy video? I mean isn't CGA and Tandy video technically the same, or did it change in anyway with Tandy video II with the SL and TL machines? The DAC is working fine with CGA but somehow it's not working with Tandy.

Or maybe the video port is just screwed... If i had an RGBi monitor i could know for sure.

Great Hierophant
April 22nd, 2017, 12:16 PM
Whatever your problem is, it isn't your DAC. Tandy Video and CGA video are the same to your DAC.

Tandy Video II added MDA & Hercules compatibility. Your video may have been set for an MDA/Hercules monitor, which means that you may not see anything from your DAC. Try pressing Ctrl-Alt-Shift-V, that changes the monitor selection. Remove your VGA card first.

April 25th, 2017, 10:50 AM
keenerb was faster giving the hint. That was the issue, the machine was stuck in mono mode.