ICL OPD (Merlin Tonto)

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Chr$
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ICL OPD (Merlin Tonto)

Postby Chr$ » Sat Aug 10, 2019 9:19 pm

I too have acquired a Merlin Tonto, but as usual the monitor doesn't work after the previous owner dropped it, rendering the whole thing even more useless that a Telephony Computer from 1984 would normally be in 2019! I do have some ICL cartridges in a 4 pack and the Xchange ROM pack etc, so it all looks good and did work before the monitor was dropped, according to the PO.

On the recent post from Pr0f I read that you can:

6.1 Change IC34 from a 74LS240 to a 74LS244 to invert the video & sync. outputs from the main board to allow the use of a standard monitor
6.2 Connect TP3 to pin 15 of J3 (solder pad above Q7) to provide a composite sync. signal for a monitor

But what about the power requirements and the general pin-out of the 15 pin power/video cable, is there any info on that? And is an old PC power supply with +12v and -5v up to the job? What have others done to get power to the OPD and to get a video signal to a modern TV/monitor? (keep it simple for me please, and pics very welcome).


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Re: ICL OPD (Merlin Tonto)

Postby Derek_Stewart » Sat Aug 10, 2019 11:02 pm



Regards,

Derek
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Re: ICL OPD (Merlin Tonto)

Postby Pr0f » Sun Aug 11, 2019 8:04 am

Power and video are towards the bottom of this web page - link below:

https://rwapsoftware.co.uk/oneperdesk/t ... _info.html

I will be putting up an update with some details on the keyboard and main connectors - hopefully later today, and will post more as I continue to delve into it.


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Re: ICL OPD (Merlin Tonto)

Postby Chr$ » Sun Aug 11, 2019 10:24 am

Thanks. Yes I saw that the OPD requires

+5 volts 3 to 3.5 Amps
+12 volts 1.5 Amps
-5 volts 0.1 Amps

And have found this old PC PSU on eBay looks to have the right voltages.

So am I right in thinking that if I change that chip to invert the video, then connect TP3 (what exactly is TP3?) to pin 15 of J3, that I'll be able to add some kind of RCA socket and get a composite signal to my non OPD monitor (or TV in this case). I've not even opened the OPD yet, but perhaps what connections go where may be more obvious if I were to do so!
Attachments
posspsu.jpg


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Re: ICL OPD (Merlin Tonto)

Postby Pr0f » Sun Aug 11, 2019 12:33 pm

TP3 will be a test pad on the PCB - I can get you a close up picture when I get home tonight, showing where that needs to be connected. I plan to make that same modification too. The -5v is required for the RS422 circuit - I can't see it used anywhere else on the board, unless of course it's also providing the negative bias on the ZX8302 ULA - see the current thread in the hardware section.

viewtopic.php?f=2&t=2940


Mine is just bare boards - no case, so could see straight away what I was looking at :-)


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Re: ICL OPD (Merlin Tonto)

Postby Pr0f » Sun Aug 11, 2019 9:01 pm

Here's a close up of the main PCB back section, where the chip swap and TP3 are:


IMG_20190811_204746.jpg


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Re: ICL OPD (Merlin Tonto)

Postby Chr$ » Sun Aug 11, 2019 10:42 pm

Oh yes, fairly obvious then. Thanks very much for that. What I don't yet get, is after that is done, where is the signal connection for the composite vid?


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Re: ICL OPD (Merlin Tonto)

Postby Pr0f » Mon Aug 12, 2019 8:43 am

This doesn't give you composite video, just composite sync.

You could use something like an AD724 to take the R, G and B signals and composite sync and produce composite video and or S-video. I suspect some resistor dividers may be necesary


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Re: ICL OPD (Merlin Tonto)

Postby Chr$ » Mon Aug 12, 2019 8:07 pm

Oh. I don't really understand video signals!

So it is possible. Will you be making composite for yours, or using the RGB?


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Re: ICL OPD (Merlin Tonto)

Postby Pr0f » Mon Aug 12, 2019 10:03 pm

For testing I am using one of those upscaler boards that handles RGB, TTL and various video formats to VGA /LCD. It has OSD that shows you the video spec coming in too - which is quite handy. Works a treat on the QL video output - I think they call them CGA / Arcade to VGA.

I am not quite sure what I will do with it once I have / if I can resurrect it. It may become a bit of an engineering mule - hence the various sockets that I've soldered or replaced the chips with. Since I have no data on the ULA3 other than it's pin out, I will replace it with GAL / TLL / CPLD logic to do what I want.



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