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Re: ICL OPD (Merlin Tonto)

Posted: Sun Aug 11, 2019 10:24 am
by Chr$
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!

Re: ICL OPD (Merlin Tonto)

Posted: Sun Aug 11, 2019 12:33 pm
by Pr0f
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 :-)

Re: ICL OPD (Merlin Tonto)

Posted: Sun Aug 11, 2019 9:01 pm
by Pr0f
Here's a close up of the main PCB back section, where the chip swap and TP3 are:


IMG_20190811_204746.jpg

Re: ICL OPD

Posted: Sun Aug 11, 2019 9:05 pm
by Pr0f
As Promised, some further updates - a picture of the board with a few sockets in place ready...

IMG_20190811_204916.jpg



also the back of the board, ready for the video mods

IMG_20190811_204746.jpg



Finally - here is an updated pdf with the latest reverse engineering...


opd decoding.pdf
(179.49 KiB) Downloaded 56 times

Re: ICL OPD (Merlin Tonto)

Posted: Sun Aug 11, 2019 10:42 pm
by Chr$
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?

Re: ICL OPD (Merlin Tonto)

Posted: Mon Aug 12, 2019 8:43 am
by Pr0f
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

Re: ICL OPD (Merlin Tonto)

Posted: Mon Aug 12, 2019 8:07 pm
by Chr$
Oh. I don't really understand video signals!

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

Re: ICL OPD (Merlin Tonto)

Posted: Mon Aug 12, 2019 10:03 pm
by Pr0f
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.

Re: ICL OPD (Merlin Tonto)

Posted: Fri Aug 16, 2019 10:38 pm
by Chr$
I'm going to see if my monitor may be salvageable first. I changed the main RIFA cap that goes over the mains input (it was blown, very obviously blown). The monitor powers up, brightness control works, leds are on, but all it shows is a long horizontal bright line. Reading up, it looks like it may be something simple. So I've taken it an old-school TV repair man (first CRT he'd seen for years) in the hope that he can get it going. Fingers crossed.

Re: ICL OPD

Posted: Fri Nov 22, 2019 7:49 am
by vanpeebles
Merged the two big OPD threads together :)