getting (PAL) composite signal from the ORIC
-
- Flight Lieutenant
- Posts: 322
- Joined: Thu Sep 21, 2006 7:45 pm
- Location: 26000 Valence, FRANCE
- Contact:
getting (PAL) composite signal from the ORIC
Supposedly the signal entering the UHF modulator in my ORIC Atmos is a PAL video composite signal. So I tried to extract it to send it to my parent's TV but it didn't seem to like it. Had some ghost-like image but it didn't seem to synchronize to it. I tried to amplify and/or invert (with a transistor in the way discussed in Theoric 1) it and tune RV1 but it didn't help. Anyone succeeded there ?
Forcing the format to PAL on the TV didn't help either.
I'll have to look closer to the form of the signal but my oscilloscope is quite old and not really reliable.
Forcing the format to PAL on the TV didn't help either.
I'll have to look closer to the form of the signal but my oscilloscope is quite old and not really reliable.
- Silicebit.
- Flight Lieutenant
- Posts: 313
- Joined: Thu Jan 12, 2006 10:18 pm
- Location: Madrid, Spain
- Contact:
Did you ever got anywhere with this hack?
I have just become the proud owner of my first (!) Oric-1, a 48K model in visually very nice condition. It was sold as spares/repair on eBay (some of you may have seen it) because it didn't do colour!
I have adjusted the two externally available knobs without getting any colours. Then I opened it and begun fiddling with the channel selector pot on the RF modulator. I found that if I push it down with a screwdriver, I get a colour display! The harder I push, the stronger the colours appear.
I've read that the RF modulators can be poor, and frankly I don't know if I can fix this in an easy way.
However I own a 48K ZX Spectrum which I performed the composite video hack on last year. It consists of desoldering the resistor to the RF connector, route the composite video in directly to the connector and ... I think that was it. To me it looks like the RF modulator in the Oric looks identical to the one in the Spectrum, so I had expected it work in the same way. Some web pages mention that you should amplify the signal from the Spectrum too to get a proper composite video signal, but I found it works out of the box.
Now, I read your message that you failed doing likewise on your Oric. I have for obvious reasons not yet pulled out the soldering iron to my brand new purchase, but if you think it would work - and more importantly give me a colour picture - I'd do it as soon as I have the time. For me a composite video signal is to prefer over RF anyway.
I have just become the proud owner of my first (!) Oric-1, a 48K model in visually very nice condition. It was sold as spares/repair on eBay (some of you may have seen it) because it didn't do colour!
I have adjusted the two externally available knobs without getting any colours. Then I opened it and begun fiddling with the channel selector pot on the RF modulator. I found that if I push it down with a screwdriver, I get a colour display! The harder I push, the stronger the colours appear.
I've read that the RF modulators can be poor, and frankly I don't know if I can fix this in an easy way.
However I own a 48K ZX Spectrum which I performed the composite video hack on last year. It consists of desoldering the resistor to the RF connector, route the composite video in directly to the connector and ... I think that was it. To me it looks like the RF modulator in the Oric looks identical to the one in the Spectrum, so I had expected it work in the same way. Some web pages mention that you should amplify the signal from the Spectrum too to get a proper composite video signal, but I found it works out of the box.
Now, I read your message that you failed doing likewise on your Oric. I have for obvious reasons not yet pulled out the soldering iron to my brand new purchase, but if you think it would work - and more importantly give me a colour picture - I'd do it as soon as I have the time. For me a composite video signal is to prefer over RF anyway.
Anders Carlsson
-
- Pilot Officer
- Posts: 74
- Joined: Thu Dec 28, 2006 11:07 pm
- Location: SOUTH WALES UK
Well, true. Personally I'm rather mediocre at soldering, but believe I could manufacture a cable myself from the diagrams on Internet. But I didn't quite understand if the RGB is TTL, half-TTL or something else. In the mean time, composite video would be the simplest mod if it worked out.
Anders Carlsson
-
- Officer Cadet
- Posts: 37
- Joined: Sun Feb 05, 2006 11:06 pm
- Location: Toulouse, France
- Contact:
I used a OPA350 for a similar kind of composite mod for an Atari 2600 Secam, and it worked fine (video signal was about 0.2Vpp too at the entry of the RF modulator).mmu_man wrote: I found later in the ORIC service manual that this signal is only 0.2 V pp.
I should probably try some single-chip video amp or a fast enough op. amp.
I was recently reading up about the Sam Coupe and noticed they used a motorola MC1377P chip to convert between RGB and composite. The data sheet is here...
http://www.datasheetcatalog.org/datashe ... 1377DW.pdf
The only problem is it requires a minimum of 10volts to drive it. Internally one might use a voltage doubler to get it but externally it would require an external psu.
Interesting tho
http://www.datasheetcatalog.org/datashe ... 1377DW.pdf
The only problem is it requires a minimum of 10volts to drive it. Internally one might use a voltage doubler to get it but externally it would require an external psu.
Interesting tho
-
- Officer Cadet
- Posts: 37
- Joined: Sun Feb 05, 2006 11:06 pm
- Location: Toulouse, France
- Contact:
You can take a cheaper route with a more modern AD724 for instance.
http://www.analog.com/en/digital-to-ana ... oduct.html.
Runs on 5V.
http://www.analog.com/en/digital-to-ana ... oduct.html.
Runs on 5V.
Twilighte wrote:I was recently reading up about the Sam Coupe and noticed they used a motorola MC1377P chip to convert between RGB and composite. The data sheet is here...
http://www.datasheetcatalog.org/datashe ... 1377DW.pdf
The only problem is it requires a minimum of 10volts to drive it. Internally one might use a voltage doubler to get it but externally it would require an external psu.
Interesting tho
This actually sounds like a good option.. it could be implemented internally so long as the power unit provides at least 10v. the 7905 inside the oric should tolerate well over 12v input before throwing the toys out of the pram, and I'm guessing the quality would be fairly good if implemented well. Might have a go at this myself as my modulator has long since died, and my old Amstrad color RGB monitor which i use for my Oric is on its last legs!
T