If you want to ask questions about how the machine works, peculiar details, the differences between models, here it is !
How to program the oric hardware (VIA, FDC, ...) is also welcome.
I don't think your Oric is broken, more likely that the Sync output from Oric is not compatible with the board you are using (wrong level, wrong polarity, or just not configured/wired right).
Is Sync connected?
Remember Oric only provides composite sync, not H/V separate, so the board will need to be able to handle composite sync on a single input. If expects (demands) separate H/V sync there are chips that do that (LM1881 and others), but hopefully the board can be configured to take CSYNC.
No, the sync is combined. I think I mentioned it earlier in this thread, the schematic is basically a copy of the "Oric to scart video converter" found here http://www.defence-force.org/computing/ ... are/video/
since this is going into a SCART connector, it doesn't make sense (to me at least) to spilt sync into HSync and VSync, as SCART doesn't have that feature.
And - for now, the testing includes only a SCART TV and the oric to scart video converter as mentioned above.
So you made a direct cable from RGB to Scart and connected it to the input Scart of a TV... There could indeed be some kind of incompatibility with signals (I don't know if you put some resistors or additional circuitry) but the main suspect (for me) is the SYNC signal. Either it is not well connected (wrong ping, bad contact, shortcut...) or its ground (pin 17 or 18, don't know for sure) is unconnected to the rest of the ground signals).
Just worth checking. On my first attempt, I made several mistakes like that, but I am terrible at these matters... I am not at all a reference
EDIT: Now that I mention it... could it be that there is an error in all those schematics and it is pin 18 (SYNC input GND) which should be put to ground and not pin 17 (SYNC output GND)? http://www.nightfallcrew.com/gallery/ul ... pinout.png
peacer surely connected both to GND and I am not sure now, but I think I remember I had to do it too (not sure, would have to open my cable to check)
Tried with pin 18 connected to ground - no change.
The my PCB has a female SCART connector, and the SCART cable I use is fully wired, like this: http://pinouts.ru/VideoCables/VideoTvScart_pinout.shtml
So pins in the are crossed like this
17 - 18
18 - 17
19 - 20
20 - 19
these pins are also crossed in the cable, but not used in my circuit
1 - 2
2 - 1
3 - 6
6 - 3
(the rest of the pins are wired straight through). Attached is a picture of the PCB I've made.
Attachments
Last edited by tingo on Tue Feb 05, 2019 2:40 pm, edited 1 time in total.
Thanks for trying... it was worth it, though unsuccessful.
Then I ran out of ideas, to be frank. My cable is a direct connection from the Oric's port to the SCART, with the addition of voltage to select the RGB mode and everything works nicely. Could it be that the SYNC signal is being filtered by the circuitry a bit too much? maybe delayed?
(I'd say try and make a direct connection, but I am quite sure you did and it didn't work, so you went for the additional hardware...)
It would be very easy to diagnose the problem if you have an oscilloscope ...
IMO are 2 possibilities:
- missing Sync signal - check everything again, follow the tracks on PCB, are all chip pins well inserted in the socked, check the transistor responsible for the Sync signal.
- bad Sync signal level - what chip is it? HCT/HC should be OK! The TTL (LS/S/H) are not recommended. Bad signal level can be very low but also very high - and this can be the secret here! If your power supply is regulated try to lower the voltage to +3V (instead of 5V, don't care about the pin 8 for now). If your PSU voltage is fixed try to use 2x1.5V batteries for test. Are there any difference with lower voltage?
And here is a test picture which shows the problem:
Test picture shows that neither horizontal nor vertical are locked, unless you leaned over while taking the picture
If horizontal was locked, your white-border would be vertical. As they are sloping \ \ that way, the TV is scanning horizontally faster than the timing that Oric is producing, so each line is turning up later than expected (and is shifted right).
So it looks like you have no sync and the TV is trying its best, but failing.
Yes, I'm thinking that the problem is that the TV don't get sync, and I think it has to do with the SCART cable, as I mentioned in an earlier post. So now I'm making a new PCB with sync going to pin 19 of the female SCART connector on the PCB. The cable will make the sync signal arrive at the pin 20 on the other end. We shall see if this fixes the problem.
Tested a new version of the circuit today, where I've wired Sync to pin 19 of the female SCART connector (since the SCART cable makes it arrive at pin 20 on the other end. Yes - that was it - I now have picture on the TV used for testing:
Nice!
FWIW, 5V on pin 8 of the SCART connector doesn't maytter for the TV.
