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Olivetti M24 - No POST

barythrin

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Yeah I would definitely try that. From what I recall (obviously I didn't play with many due to price) early LCD monitors weren't very compatible ironically with many signal types. They seemed almost like a winchip equivalent of monitor, supporting only popular resolutions and scan rates commonly used in Windows.
 

Chuck(G)

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Well, as you've show, you own a 'scope so you can easily determine the H and V sync output frequencies probably faster than I can type this. I run a 19" ASUS LCD monitor on mine and it works fine.
 

ChrisCwmbran

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I probably phrased the question wrongly there really sorry. I understand about the frequency of pulses on the horizonal and negative sync pins, and I understand the concept of a negative sync on horizonal. I really was hoping to understand a bit about the nature of a valid signal for the RGB components, and how the data on them is encoded (perhaps).

I've also been trying to find a suitable explanation of how sync works on a composite signal too i.e. where a monochrome composite video signal is carried over a phone cable. I guess it's part of trying to understand what a scope can and can't be used to test.
 

Chuck(G)

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The M24 video is simple RGB+I and the VGA adapter ignores the I signal. TTL levels on everything. One of these days, I'll work out a little circuit to use the I output and clamp the outputs to 1V p-p. But it works as-is for now.

So to use a scope, set 1 or 2 v/div, sync on auto, and adjust sweep rate so that you can see two pulses. You then can see the time between the leading (or falling) edges of any two consecutive pulses. The frequency is simply the reciprocal of that.

For example, let's suppose you've cranked the sweep rate to 5 milliseconds/div and you see two pulses. Looking between two consecutive leading pulse edges, you see 3 divisions plus a bit or about 16 msec. between the pulses. The frequency is then 1000 msec./second divided 16 msec. or about 62 Hz.
 
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ChrisCwmbran

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Ok the settings I found are as follows:


DIPSW1 J5 ON J6 ON Pin 1 (H Sync) 4.9v pk to pk, 25.9kHz
Pin 2 (V Sync) 4v pk to pk, 60Hz
Pin 4 (Red) 3.6v pk to pk... randomish pulses
Pin 5 (Green) 3.6v pk to pk... randomish pulses
Pin 6 (Blue) 3.6v pk to pk... randomish pulses

DIPSW1 J5 OFF J6 ON Pin 1 (H Sync) Signal about 0.16v
Pin 2 (V Sync) Signal about 0.16v
Pin 4 (Red) 3.6v pk to pk... randomish pulses
Pin 5 (Green) 3.6v pk to pk... randomish pulses
Pin 6 (Blue) 3.6v pk to pk... randomish pulses

DIPSW1 J5 ON J6 OFF Pin 1 (H Sync) Signal about 0.16v
Pin 2 (V Sync) Signal about 0.16v
Pin 4 (Red) 3.6v pk to pk... randomish pulses
Pin 5 (Green) 3.6v pk to pk... randomish pulses
Pin 6 (Blue) 3.6v pk to pk... randomish pulses

DIPSW1 J5 OFF J6 OFF Pin 1 (H Sync) 4.9v pk to pk, 25.9kHz
Pin 2 (V Sync) 4v pk to pk, 60Hz
Pin 4 (Red) 3.6v pk to pk... randomish pulses
Pin 5 (Green) 3.6v pk to pk... randomish pulses
Pin 6 (Blue) 3.6v pk to pk... randomish pulses

I also tested them with my adapter cable and found a problem with the HSync pin not making a good connection. I havent had a chance to correct that and try it on a monitor yet.

Aren't those 0.16v signals a bit odd?
 

Chuck(G)

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0.16V falls into the category of "noise"--electrically insignificant. Those randomish pulses on RGB are what one would expect to see--they're the individual pixel dots. So, something is coming out of the card.

I'll do some readings on my own setup and see how things compare. 25.9KHz does work out for 60Hz vertical to 431 lines--reasonable for a 640 × 400 display. I may be lucky with my VGA LCD being able to sync to that.

However, the DIP switch settings for 5 and 6 don't make a lot of sense. Are you power-cycling between changes?
 
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ChrisCwmbran

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When you say power cycling between changes I assume you mean each time we change the dip switches in which case the answer is yes.

We didn't power cycle between taking readings from individual pins though.
 

Chuck(G)

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A quick check with mine yields a horizontal sync of about 25.7KHz, 4.2V positive-going, 4usec pulse.

Close enough. Pick a good monitor--apparently not all VGA LCD monitors will sync down to 25KHz.
 

ChrisCwmbran

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Ok, thanks for taking the time to test that Chuck. I'll do some more testing :)

My mum is really excited to see the M24 running again! I get asked everyday. Back in the 1980s she wrote her thesis on one back when she did he Music degree!
 

ChrisCwmbran

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Whilst waiting to be able to pickup a suitable VGA monitor to test this I thought I'd have a look in the back of the M24s own monitor and see if I can see any problems.

What the hell is this? If you look at the last picture it doesn't look too good!!!!

IMG_20120722_183827.jpgIMG_20120722_183836.jpgIMG_20120722_183850.jpg
 

Chuck(G)

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Well, the resistor is a 6.2 ohm, 10 watt unit. These tend to get very hot (that's why they're called power resistors). But yours looks to have issues with corrosion.

Can't say much about Olivetti's monitors, other than I think they were made by Hantarex Italy. Is that the monochrome monitor?
 

Chuck(G)

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Looked at the innards of my (monochrome green) monitor. It's nothing at all like yours--to start with, all the component silk-screening has components starting with 1, so I see R23, C10, etc. Not R903.

No big power resistor, either. I wonder if that monster in yours is a cheap attempt to drop the +15 supply to +5 for logic. If so, there are other, more efficient ways to do the job. Any identifiers as to who the maker might be and the model number? Sometimes on a bit of paper, silk screening on the PCB, or etched on the foil side of the PCB.

My monitor looks like this one:

0.jpg
 

ChrisCwmbran

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No labels on mine.... or at least there is one internal label but it is completely faded.

Searching in google for "Olivetti M24 monitor" the first 5 images are from a site called "olivetti.isgreat.org" that appears to be gone, however they appear to be of the same monitor I have, and one of them is a sticker that says it is made by "Goldstar".

I think it says its an "MBN-21318" but its quite hard to be certain:

Goldstar.jpg
 

Chuck(G)

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So you're good now?

It's curious that the AT&T 6300 used an Italian monitor, but the M24 seems to have used a Korean one. Maybe someone has an idea of why...
 

ChrisCwmbran

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Yeah I don't forsee any problems now.

Thanks for everyones help. I'll post some better pics of the machine when it is all in one piece and booting DOS nicely!

I would still like a set of newer ROMs for this machines and full details of any expansions/mods that are worth doing if anyone can help! :)
 
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