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IBM 3270 PC (5271) with MDA 5151 monitor

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nolan7

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Oct 17, 2015
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Slovakia
I have a complete 3270 with 5272 color monitor and 122-key keyboard and everything is working correctly. Aside from that, I had bought for cheap a second 3270 without keyboard and monitor, which was converted to normal XT in the past, so it was missing all special cards and looked like normal XT with MDA inside. Only differences were badges in front and back, so apparently it was 3270. Over time, I bought all necessary cards and wanted to convert it to fully equipped 3270. I've put all cards inside and connected original terminal keyboard and 5272 monitor. Computer turned on, but picture was jumping like it was out of sync, still I was able to see that it is counting memory, 16 KB OK etc. I switched it off, didn't want to burn anything. Then I was using the computer with MDA card and 5151 monitor, everything worked OK, computer was starting without any beeps or errors. (I was using it with all 3270 cards inside plus MDA card all installed together) Because I have read on John Elliott's webpage, that 3270 graphic card should detect which monitor is connected and set video mode accordingly, and hadn't second 5272 monitor, I wanted to have this second 3270 to use normal MDA monitor with original 3270 videocard. So I connected 5151 to the other video output (on the 3270 video card) and switched it on. I could hear monitor making nasty sound as if something is out of sync, and knowing that MDA monitors are sensitive, I thought I killed it. So I connected it back to the MDA card and switched computer on again. It started with one long and two short beeps, and showed error 3201. Monitor survived, nothing happened to it, but something else went bad. By trial and error I figured that 3270 graphic card got bad. If it is in PC, it makes that beeping sound and shows error 3201. If I switch it for another known good 3270 card, it stops doing it and everything is working OK. I tried it also with 5272 monitor and it works. But the other card is bad, sadly. Now I have a few questions:

1. Was the card in second 3270 PC bad from start, because it showed rolling picture on 5272 monitor (even if I could still see characters so it was working somehow) and connecting to 5151 just killed it absolutely? Because from start, it was not showing error 3201 on boot up and beep. So something went terribly wrong when connected to 5151. I thought that monitor will die, but, the card did. :(

2. Is it safe to connect 5151 monitor to my first nice lovely complete 3270 PC? I don't want to kill another card, they are hard to find... Anyone here can confirm this for sure, that it is safe combination and it works? Without any reconfiguration, just to switch monitors from 5272 to 5151 and it should work?

Thank you for your answers.
 
I had a 3270 PC before, and the video card it uses is not compatible with anything but the 5272. Tried it with a 5153 and 5151, neither worked. The card was fine afterwards too, so I bet the card you had was bad to begin with. Usually, if you mismatch video circuits, it'll maybe damage the monitor, but not the card.
 
The 5271 and 5273 display adapters are definitely compatible with the 5151. That is how I use mine as somehow I've ended up with three 5272s, none of which work.
 
I must be mistaken then. I could have sworn I tried testing it with my 5151 and it not working, but now I think I must have only tried my 5153. Come to think of it, I think I might have remembered seeing the 5151 being advertised with the 3270PC as a lower cost alternative to the 5272.
 
willmurray461 said:
I must be mistaken then. I could have sworn I tried testing it with my 5151 and it not working, but now I think I must have only tried my 5153. Come to think of it, I think I might have remembered seeing the 5151 being advertised with the 3270PC as a lower cost alternative to the 5272.
Click to expand...

The manuals are here:-

http://www.bitsavers.org/pdf/ibm/pc/3270_PC/

and no where can I find a reference to setting links or switches on the display board, but it implies both displays just work
 
I have a, perhaps working, motherboard. The, perhaps working, cards, and a, perhaps working, monochrome monitor. I could do a test ;)
 
I did do some testing...

Motherboard with VGA card works.
VGA card and timer/keyboard card: No video output

Motherboard with Hercules clone card works
Hercules and timer/keyboard card: Still works

Motherboard with timer/keyboard card and 3270 graphics card: Doesn't work on my monochrome monitor. I got a bright flashing vertical line at the top of the screen. The flashing makes me think, that text was actually being displayed - but the sync was missing or incorrect for the monitor.

Motherboard with timer/keyboard card, 3270 graphics card and Hercules card (monitor connected to the Hercules card): Works fine. No beeps or extra error messages.

So I think I can confirm, that the 3270 graphics card does not work on standard monochrome monitors. Perhaps there was more than one version?

My monitor is not an IBM 5151, but a Rose-branded monitor from Taiwan. But shouldn't different MDA-compatible monitors behave the same?
 
I frequently use my 5151 with the 3270 graphics card. I can’t remember exactly, but there is a pin which the card uses to detect which monitor is attached.
 
Did some measurements. With my Hercules clone card, I get a Hsync frequency of 18.14kHz, and 49.03Hz for Vsync. With a different monochrome card (MDA clone or Hercules clone? - don't know), I measured 18.13kHz and 49.01Hz. So those two agree at least...

On the 3270 graphics card I measured 18.43kHz and 49.94Hz (with no monitor connected), which should certainly be in-range for the monitor.

So why didn't it work? Did the monitor somehow fool the card into thinking a colour monitor was connected?
 
Important update time...

My 5160 mainboard behaved strange with other graphics cards, so I tested the 3270 graphics card in a turbo XT mainboard now. And:

attachment.php


So yes, a monochrome monitor will work - you just need a fully working mainboard. And an IBM mainboard is not needed.

Only slight bug is the flashing cursor, where a '6' should be.
 

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Thank you, so it looks like it should work... so probably my card was already bad... I am going to try it today with another working one.
 
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