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Olivetti M24 display

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vladstamate

Experienced Member
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Dec 2, 2012
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197
Location
Orlando, FL, USA
Hey folks,

I want to get an Olivetti M24 but it does not come with a monitor. Now it seems that while the display is an enhanced CGA, the connector is not a normal CGA.

Am I correct about that? Also, what are my options to display something from the Olivetti? What about installing a normal CGA card?
 
Hi all,

I am finally in a possession of the Olivetti M24, the Olivetti monitor (the monochrome one I believe) and a keyboard that is neither Olivetti nor AT&T but it has the same connector (I believe from Xerox word processors). So when I power on the machine, it makes all the right noises (turning on the motor of the floppy, the HDD, just like it is trying to boot) but I get nothing on the display. Now there are multiple options here:

1) There is something wrong with the display
2) There is something wrong with the output from the computer
3) The computer is set to run from a secondary graphic card.
4) Something else entirely (like the keyboard is not ok).

I would like to eliminate 3) first, as it is easy. Especially because the computer came with a missing metal cover for one of the ISA slots, indicating that something could have been there.

So I would like to look at the actual motherboard, on the underside but I do not know how to get to it. Do I have to dis-assemble all the insides (like the drive cages and the PSU) to get to it, or is there an easier method?
 
The motherboard is mounted upside-down, so you need only remove the bottom cover for the motherboard.

However, take a look at the (two) display cards. Check the jumpers and look for any missing ICs. One of the more popular ways, it seems to disable the video display was to simply pull one of the PALs (and lose it!). That was the case on mine and I managed to work out the needed equations so that a regular 16V8 GAL can be programmed.
 
Thank you. I knew it was underneath I just did not know initially how to take the bottom off. But now that I did it and inspected both the motherboard and the videocard it seems nothing is missing, and all is nice and clean (even the battery has not leaked, but i will change it shortly). I verified that the DIP switches were correct.

After that I measured 15V on pins 24 and 25 of the video port, so the monitor is definitely getting power.

Then I connected an oscilloscope and took a peek at H and V sync and they seem fine (60Hz frequency on my scope). (although I will mention one strange thing that both H and V were 60Hz however when zooming in with the scope it showed a higher frequency signal being carried by the 60Hz big signal).

However the monitor still shows no life, so my guess is, given that the computer is going through the booting motions that either

1) There is something wrong with the monitor
2) Or something else...
 
I would not connect an unknown keyboard to the machine without checking compatibility before. You can damage keyboard and machine. The M24 keyboard interface is special, non standard and not compatible else than: M21. M24. M28. AT&T 6300. Logabax Persona 1600. Xerox 6060 (Xerox and Logabax are relabled M24).

Note, that there is also newer Olivetti PC, M240, M280 which use the same connector, but as far as I know, incompatible to M24 connector, they use AT keyboard protocol.

Please show your keyboard here. Maybe it is Xerox 6060 keyboard. Then you are lucky.
 
Thank you for checking that. The system seems to be partly alive!

I have soldered a VGA connector and rewired the DB25 to DB15 and connected it to a VGA monitor and now I get this:
IMG_0023.jpg
It stays there and does not go further.

So it does seem that maybe there is a problem with my Olivetti display.

However what should happen next? Should it boot from the HDD?
 
Well I do not have the original Olivetti keyboard. The Xerox keyboard I have has only 2 LEDs: one for Caps Lock and one for Num Lock. They seem to be both lit all the time.
 
Hmmm, during the POST diagnostics, the LED on the regular M24 flickers, I guess to show that the keyboard is communicating.

On the other hand, could it be that the display board really works, but your VGA monitor isn't adjusting to a change in sync frequencies? A scope on the H and V sync lines would show this.
 
I think display is is allmost Ok. It stops after checking first 128 kB.

You should open the lower case where the mainboard is placed upside down in the bottom and see how much memory is installed. Only 128 kb or 640 kb (half of the memory sockets populated, or all?)

Next step of M24 after checking memory is harddisk (option-rom at c800) and then floppy drive.
 
Chuck(G) said:
Hmmm, during the POST diagnostics, the LED on the regular M24 flickers, I guess to show that the keyboard is communicating.

On the other hand, could it be that the display board really works, but your VGA monitor isn't adjusting to a change in sync frequencies? A scope on the H and V sync lines would show this.
Click to expand...

I already checked and posted that info a few posts above. I am seeing 60Hz on the Vsync pin and something similar on the Hsync, however there is a much higher frequency signal encoded over that one. That coupled with the fact that I got an image on my VGA monitor once, it means the display card is not entirely broken.

However other things seem to be not alright. For example I cannot get the same image anymore on my VGA monitor again. And whether or not the CapsLock and NumLock LEDs are on depends on how many times I power cycle the computer.

I tried re-sitting all the chips which are in sockets but that did not seem to make an impact. Something is definitely loose or a bad connection somewhere.

I will try opening up the Olivetti display because that one should at least get power.

Now if it behaves the same as as the IBM 5150 associated monitor that it does not display anything if it does not get any data (even though it has current) then it would explain the monitor behavior.
 
I concur that your display board is working, since you originally got that image on the VGA monitor. However, getting a different results every time you boot is troubling; I'd ensure the battery is off the motherboard as it may be leaking acid onto traces. Also replace any capacitors that look bad.
 
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