Video cable compatible with all Scart TVs

[Robbizz]

Hi guys, I found some time to spend with my QL and I built a Video Scart cable myself. I followed the diagram below (the sockets are seen from the front, NOT the solder side). It works very well with a couple of TVs at home but on a small TV/Monitor (where among other things I would like to always keep it connected to my QL), it doesn't work: on the latter TV there is a message "no signal" when I turn it on and then - when I press F2 - I see a red image out of sync. The resistors are 390 Ohm. What do you think it could be?

[martyn_hill]

Hi Robbizz!

[Edited to correct SCART pin numbering in original post]

I've had success creating a number of QL -> SCART cables over time, based more or less on the really useful site:

http://www.fruitcake.plus.com/Sinclair/ ... ableQL.htm

I guess you might have used the same site and, like me, you've used that 'trick' to use the Comp. PAL Video (QL pin-1) output to drive BLANKING (SCART pin-16) as a convenience to present c. 1V+ and thus trigger the TV/Monitor in to RGB mode (vs Comp. Video.)

However, as per that site, I also add the 330ohm resistor in series with the TTL CSYNC signal in to SCART pin-20 (Video-in), effectively lowering the CSYNC signal presented at Video-in to around [75 / (330 + 75) x 5V =] 0.93V pk.

Some TV/monitors might be sensitive to the TTL level appearing on pin-20, so I recommend adding that series resistor to effectively lower the pk voltage present at Video-in.

Again, referring to the above site, I've never needed to drive the FUNCTION pin (SCART pin-8), but again, some TVs might be fussy, though the effect you describe doesn't sound relevant to driving this pin.

Let us know how you get on!

[Robbizz]

Hi Robbizz!

I've had success creating a number of QL -> SCART cables over time, based more or less on the really useful site:

http://www.fruitcake.plus.com/Sinclair/ ... ableQL.htm

I guess you might have used the same site and, like me, you've used that 'trick' to use the Comp. PAL Video (QL pin-1) output to drive BLANKING (SCART pin-16) as a convenience to present c. 1V+ and thus trigger the TV/Monitor in to RGB mode (vs Comp. Video.)

However, as per that site, I also add the 330ohm resistor in series with the TTL CSYNC signal in to SCART pin-18 (Video-in), effectively lowering the CSYNC signal presented at Video-in to around [75 / (330 + 75) x 5V =] 0.93V pk.

Some TV/monitors might be sensitive to the TTL level appearing on pin-18, so I recommend adding that series resistor to effectively lower the pk voltage present at Video-in.

Again, referring to the above site, I've never needed to drive the FUNCTION pin (SCART pin-8), but again, some TVs might be fussy, though the effect you describe doesn't sound relevant to driving this pin.

Let us know how you get on!

Thanks for the suggestion. I tried to put a 330 Ohm resistor in the point indicated by the arrow, but unfortunately I still receive no signal (when there is the initial F1-F2 screen) and then I see the screen as per the disturbed photo (exactly like before).
Note that with the same cable, on my TV at home, it works perfectly (see last photo).
I don't think that the Samsung TV has problems managing RGB signals, because I tested it using an Atari ST with Scart cable and it looks good.

[martyn_hill]

Hi again Robbizz!

OK, so all I personally can think-of is that this monitor doesn't like the QL's 'over-scan' timing and is struggling to sync properly.

(BTW, as you observed, I misnamed the SCART Video-In pin - yes,its pin-20, not 18.)

Keep us posted

[dilwyn]

Probably not very relevant here, I don't know, there was sometimes an issue if a Gold/Super Gold Card was involved. One eBay supplier made different SCART monitor leads for QLs with Gold Cards or Super Gold Cards (maybe both, can't remember).

I've had a look for the explanatory paperwork which came with the lead, but can't find it - it's probably in one of the computer junk boxes in the attic with the SCART leads, as my QLs now have the VGA monitor adaptor devices instead. I think it was as simple as either an extra resistor or a different resistance on one pin.

If I manage to find it I'll post it here. Hope that saying this will make someone remember what the difference was!

[dilwyn]

Oops, minutes after my first post I remembered the cables I mentioned came from Retro Computer Shack:

https://www.ebay.co.uk/itm/260814300633 ... R8CBqv3uYw

Further down that page is the explanation regarding the extra resistor for (Super) Gold Cards:

Retro Computer Shack SCART leads

Those leads cost £14.49 including postage.

[XorA]

Probably not very relevant here, I don't know, there was sometimes an issue if a Gold/Super Gold Card was involved. One eBay supplier made different SCART monitor leads for QLs with Gold Cards or Super Gold Cards (maybe both, can't remember).

They use the CSYNC as ram refresh signal, so squashing it to zero volts by connecting to SCART does not go well. I reported the issue to RCS and he fixed future cables!

[dilwyn]

Probably not very relevant here, I don't know, there was sometimes an issue if a Gold/Super Gold Card was involved. One eBay supplier made different SCART monitor leads for QLs with Gold Cards or Super Gold Cards (maybe both, can't remember).

They use the CSYNC as ram refresh signal, so squashing it to zero volts by connecting to SCART does not go well. I reported the issue to RCS and he fixed future cables!

Thanks XorA, that's refereshed my RAM a little too.

[Derek_Stewart]

HI,

I use the cables from Retro Computer Shack, all very high quality and work on the QL RGB output to a SCART input on TV Monitor.