Modification of SCART with 100µF capacitor

[kribjo]

Hi,


Connecting my 664 or 6128 to a 7ish year old Philips LCD TV and I don't get a stable and sharp picture so I still use my 14" Nokia CRT where the scart cable delivers a clear and stable picture. Reading TV SCART cable - CPCWiki I wan't to do this myself, but I don't know nothing about how many volts the 100µF capacitor should be as it's not mentioned. And where do I buy it?


I like to buy a lot of stuff from China with free shipping. But not sure where to buy electronic parts from China. I bought some resistors a few weeks back from RS components, Norwegian branch. Sent with DHL (from RS branch in UK) which estimated total value including shipping to be >350NOK triggering extra Norwegian taxes. 20 resitors turned out to be extremly expensive. :-(
I hope someone have a link to a chinese web or even a Norwegian.


Bjørn

[Bryce]

They usually start at 10V and this is already high enough for this purpose. Buy them locally on ebay, they'll be cheaper than RS and faster than ordering them from China.

Bryce.

[1024MAK]

The voltage rating is not that critical. So you can use 10V, or 16V, or 25V rated types. 100uF 10V and 100uF 16V are commonly available values and should not cost very much. So you should be able to buy one from any decent electronic supplier. Note that this type of capacitor is polarity sensitive and must be wired up correctly. They normally have a stripe labelled "-" indicating the negative connection.

Mark

[Bjørn Kristiansen]

Thanks.


I have ordered a couple of these ones. 2X 100uF 100ΜF 10V Electrolytic Capacitors Elektrolyt Kondensatoren Elko RM2 5
Will definetly check the polarity before soldering. :-)


Bjørn

[Bryce]

The short wire goes to GND.

Bryce.

[kribjo]

I bought my scart cable from Retro Computer Shack, labeled "Amstrad CPC 464 / 6128 RGB GOLD SCART v2.2", and looking at it there are some variation comparing it to the wiki guide.


[attach=2]


while cpc-wiki looks like:




Is it safe to still solder capacitor between pin 16 and 18 when pin 17 is already linked with pin 18 and GND in cable?


Bjørn

[Bryce]

Pins 17 and 18 are grounds, and that's what the capacitor needs on pin 18, so yes it's fine.

Bryce.

[kribjo]

Yes! It worked.


So much better to use the led tv. Now I can free up space on my desk by putting my 14" crt tv in storage. :-)


Bjørn

[mr_lou]

Can there be cases where adding a 100uF capacitor will make the picture worse? Or can it always only improve the picture?

[Bryce]

The capacitor just tells the TV to stay in RGB mode and stops it from auto-scanning the other possibly inputs (Composite and S-Video). It doesn't have any effect on the picture quality, it just stops it from flickering. So no, it can't make the picture worse.

@kribjo: Congratulations on your first successful mod.

Bryce.

[mr_lou]

The capacitor just tells the TV to stay in RGB mode and stops it from auto-scanning the other possibly inputs (Composite and S-Video). It doesn't have any effect on the picture quality, it just stops it from flickering. So no, it can't make the picture worse.

Well in that case, wouldn't the best SCART cables always have this 100uF capacitor, to make sure it works on most TV's?

[Bryce]

Well in that case, wouldn't the best SCART cables always have this 100uF capacitor, to make sure it works on most TV's?

Yes, but that news hasn't made it to the ebay sellers out there. Some cables being sold use a completely different wiring and some are similar but without the capacitor. But it's up to them what they make/sell.

Bryce.

[chinnyhill10]

Yes, but that news hasn't made it to the ebay sellers out there. Some cables being sold use a completely different wiring and some are similar but without the capacitor. But it's up to them what they make/sell.

Bryce.

So many cables for various machines that I've had to modify. I suspect half the time the sellers don't even have a machine to test their cables on.

[Bryce]

So many cables for various machines that I've had to modify. I suspect half the time the sellers don't even have a machine to test their cables on.

That's my guess too. I also think that even if they do own the particular machine, they don't test all cables. It's easy to check on SCART cables. The flat terminals will be completely "scratchless" if it has never been connected. The first connection always leaves marks.

Bryce.

[mr_lou]

Yes, but that news hasn't made it to the ebay sellers out there. Some cables being sold use a completely different wiring and some are similar but without the capacitor. But it's up to them what they make/sell.

Yet you told me you don't make cables because they're available all over eBay...... 

[Bryce]

Yet you told me you don't make cables because they're available all over eBay...... 

Yes, I leave the cables to others. That doesn't mean they do it right, it just means that I don't do them

Bryce.

[1024MAK]

Part of the problem with SCART cables is that different TVs react differently to the control signals that SCART uses. Some TVs have inputs that require the sending device (your computer) to output control signals that conform to the standard. While other TVs are more forgiving.

Further, some TVs have manual override controls (on the remote, or via an on-screen menu). While others only use auto-switching.

And of course, rather a lot of 1980's computers were not designed to conform with the SCART switching signals (and in some cases, the RGB video levels either).

Mark

[Bryce]

Yes, but that only means that there are some TVs that won't work if the control signals are missing. If your cable has the control signals, it should work on any TV. Having the control signals where they aren't needed doesn't cause any issues.

Bryce.

[1024MAK]

What I am getting at, it is not practical to test every TV or (suitable) monitor. If the cable manufacturer makes and tests a design based on the typical circuit used by the retro community (for that computer). Then tests it on a selection of the manufacturers own TVs and monitors and it works. Is that enough?


Most of these cables are made by a small scale "cottage industry".


Mark

[Bryce]

What I am getting at, it is not practical to test every TV or (suitable) monitor. If the cable manufacturer makes and tests a design based on the typical circuit used by the retro community (for that computer). Then tests it on a selection of the manufacturers own TVs and monitors and it works. Is that enough?


Most of these cables are made by a small scale "cottage industry".


Mark

I understand what you are saying, but the problem is, there isn't "one cable that the community is using", there are many. The reason for this is that the first simple SCART cables were designed and published before LCD / Plasma etc existed. They were simple, but worked on every TV because there were only analogue CRT TVs at the time. Since LCD/Plasma arrived, the cable needed to be improved and several solutions came out, many of which required a battery. I improved on this again (mainly because I couldn't be arsed putting batteries in a cable and always making sure it's turned off when I'm finished) with the capacitor solution. The cottage industry tends to be churning out the very simplest solution (which only works on some TVs) and not the capacitor version (which works on many more TVs including the TVs that work with the simple cable). If the cottage industry all made the capacitor version they would cover more devices and this wouldn't change the amount of testing required.

What would be more useful, would be a list of known good and known bad TVs for retro viewing. Many TVs will not display a decent retro screen no matter what SCART cable is used, because they are too fussy about the sync frequency being absolutely perfect.

Bryce. 

[1024MAK]

I understand what you are saying, but the problem is, there isn't "one cable that the community is using", there are many. The reason for this is that the first simple SCART cables were designed and published before LCD / Plasma etc existed. They were simple, but worked on every TV because there were only analogue CRT TVs at the time. Since LCD/Plasma arrived, the cable needed to be improved and several solutions came out, many of which required a battery. I improved on this again (mainly because I couldn't be arsed putting batteries in a cable and always making sure it's turned off when I'm finished) with the capacitor solution. The cottage industry tends to be churning out the very simplest solution (which only works on some TVs) and not the capacitor version (which works on many more TVs including the TVs that work with the simple cable). If the cottage industry all made the capacitor version they would cover more devices and this wouldn't change the amount of testing required.

What would be more useful, would be a list of known good and known bad TVs for retro viewing. Many TVs will not display a decent retro screen no matter what SCART cable is used, because they are too fussy about the sync frequency being absolutely perfect.

Bryce.

Agreed 

And it is the same story for various other retro computers and the various SCART cable manufacturers.
A list (or database) of known good and known bad TVs would indeed be helpful.
I think it would also be useful if the type/make/supplier of the SCART cable(s) and which computers have been tested would make it even more useful.

Mark

[kribjo]

The capacitor just tells the TV to stay in RGB mode and stops it from auto-scanning the other possibly inputs (Composite and S-Video). It doesn't have any effect on the picture quality, it just stops it from flickering. So no, it can't make the picture worse.

@kribjo: Congratulations on your first successful mod.

Bryce.

Thanks. A simple, but important mod for me.