Super Gold Card + Scart

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XorA
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Super Gold Card + Scart

Postby XorA » Thu May 02, 2013 5:15 pm

Ok this is an odd one.

Recently got a SGC from RWAP which seems to be working fine, when using UHF output I see SGC initialization message and can do typical "Hello World".

When I use the SCART cable from Retro Computer Shack the QL will not "boot" with the SGC card in. It works fine without the SGC.

Is the PSU very borderline and I need to actually use the +5v in on the SGC with a meatier PSU?

Graeme


Nasta
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Re: Super Gold Card + Scart

Postby Nasta » Thu May 02, 2013 8:02 pm

The SGC requires the synch signals (VSYNCH and CSYNCHL) from the expansion bus connector. These are actually directly connected from the video out connector. There are many varieties of SCART connections as it's a multi-purpose connector with many signals. Based on your description I would say thet your particular connection uses the CSYNCHL signal. In some cases this signal has a very low (75 ohm) resistance to ground inside the monitor/TV expecting a 1V video-style signal. When this is connected to the QL's output, which is a 5V TTL type signal, it overloads it and reduces the normally high 5V signal levels on it to only a fraction of that. This wull not be a problem for the TV/Monitor but the lowered level it will prevent the SGC from recognizing it properly.
The SGC uses this signal to trigger RAM refresh (a requirement of dynamic RAM, such as used on the SGC), so without it the RAM is not refreshed periodically and corrupts it's contents. Since the first thing the SGC does is copies the sontents of the ROM into RAM for fast execution, the corruption sets in immediately preventing it from even booting correctly.
The remedy is to put a series resistor inside the SCART connector to reduce the 5V signal to 1V on the way to your TV/monitor. The value should be around 270-330ohms. The total load for the CSYNCHL signal then becomes much lower and the voltage whould be fine for the SGC/


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XorA
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Re: Super Gold Card + Scart

Postby XorA » Thu May 02, 2013 10:12 pm

You were spot on!

Soldered a 330 Ohm inside the SCART plug and its all sorted. I shall email RCS and tell them about the issue and hopefully they can fix that for future purchasers!

G


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dex
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Re: Super Gold Card + Scart

Postby dex » Fri May 03, 2013 12:13 am

I use their cables with SGC QL and with three different monitor types I had no problem.
Better thing than to force them to change the cables is to build analog / TTL switch for the monitor.


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XorA
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Re: Super Gold Card + Scart

Postby XorA » Fri May 03, 2013 9:49 am

Their cables already include the resistor for the RGB lines which are also TTL level. I assume your TV/Monitor just happens to have high impedance inputs!


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genetika
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Re: Super Gold Card + Scart

Postby genetika » Sun Jul 07, 2013 8:11 am

I had the same problem.
I bought a different scart from eBay.

Kind regards,
Massimino



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