IBM 5155 for sale; using CGA on modern monitors with RGBtoHDMI+Pi


Fred M
 

Hello all,

I have an IBM 5155 for sale, in case anyone is interested. I can include an XT-IDE card and an RGBtoHDMI+Pi Zero.  More on that in a bit.

I've also been experimenting with ways of connecting the machine, configured with a CGA graphics card, to contemporary monitors. I thought I'd report on that, too.

I bought a CGA2RGBv2 adapter (https://gglabs.us/node/2063), and I was able to get a usable image from the computer using an Extron RGB-HDMI 300A scaler. Even then, it took some time to adjust the settings (using "auto-image" completely squashed the image). I also tried a DVS-304 DVI, but had no luck with that. 

I tested on three Dell monitors--two 16:9 aspect ratio P2419Hs and a 5:4 aspect ratio P1917S. The interesting thing is that when using the VGA connector, the P1917 (made in 2016) and one of the P2419Hs (made in Sept 2020) will sync using just the CGA2RGBv2 alone; the resolution reported by the monitor is 1440x240. The other P2419H, built in Dec 2018, won't. I checked with an IBM 5150, too. The service menus of the two P2419Hs look very different, and the firmware appears to be different. I would be interested to hear if anyone has had any luck connecting 15Khz machines--PCs or other types of machines--to other monitors with VGA that have come out in the last 5 years.

Note that http://15khz.wikidot.com/ lists partial support for 15KHz signals for the P1917S. The P2419H is not listed, but the P2214H is. Earlier this year, I tested a P2414H, and it seemed to work fine, too.

I was testing all of these by running through the video tests of Checkit 3.0.

I also experimented with using a Raspberry Pi Zero with an RGBtoHDMI hat ( https://github.com/hoglet67/RGBtoHDMI/wiki) which I soldered together. The image was super crisp. I did have a bit of trouble getting the Checkit screen completely visible while working with the P1917S. Ultimately, I had to use interpolated 4:3 mode. I didn't have any problems with the wide-screen P2419H, however. One convenient thing about the wide screen Dells is the ability to change the aspect ratio between 4:3/5:4/16:9. 

So:
  1. The CGA2RGBv2 can be used in general with the Extron 300A to get a usable image.
  2. The P1917S and *some* P2419H displays sync without the Extron scaler. When the monitors are compatible, the CGA2RGBv2 alone works well.
  3. The RGBtoHDMI took some tweaking with the 5:4 aspect ratio of the P1917S, but otherwise it looks great, both on that monitor and on 16:9 monitors.
I'm very pleased with the RGBtoHDMI so far (the pics are for it). It seems to be a bit sensitive to movement and the quality of cables used, but that might just be poor workmanship on my part. I've used it with a BBC-Micro as well, and the image is again super crisp. 

Now, about that 5155, I ran checkit 3.0 on it, and it appears to check out. It has a large scratch down one side, but otherwise is in good cosmetic condition. The CRT currently works, but it needs new caps and tuning (when contrast and brightness are cranked up, the image blows up). The little latch on the keyboard connector has broken off, but the keyboard still works. 

The floppy drive test indicated an error on the first disk I tried to test, but after I cleaned both the A & B drives, both passed checkit's test. The machine currently has an XT-IDE drive with a formatted CF card in it. I'd like to keep that, but if you would prefer to pay a bit more for it, that would be OK, too.

I've included a few pics. If you're interested, please let me know. I can include the RGBtoHDMI+Pi, too.

Fred