Amiga to VGA to VGA Breakout to GBS-8200 RGB Problems

[tpgb12]

The GBS-8200 from what I've read on here only takes 31khz through its VGA in, so in order to use a Amiga to VGA adapter I got recently I assume it would only work through a VGA breakout board.

I've wired up the VGA breakout board using the cable the GBS came with. I plug that into the socket (above the VGA in) and either my Amiga's power light starts flashing and nothing else happens, I get some random colors changing with what I'm doing in a game, a very scrambled image of the game for only a few seconds, or just no signal. I also tried this setup with another computer, my PC-98, and it also gave me at best a scrambled image for a few seconds. I know my GBS works since it displays my supergun just fine.

So, am I wiring it wrong or what? I've attached an image of my wiring so far and would very much appreciate it if anybody can confirm what I may be doing wrong. Thanks.

[jbilander]

The Amiga normally runs at 15 kHz for games (pal or ntsc). Even if using a DB23 to VGA-adapter the signal sent from the Amiga is 15kHz although buffered, you would need to run e.g. DblPal mode to get up to Vga frequency range (31 kHz) and that would only be for WB on A1200 or better, not games. You can use Csync (RGBS) out from the Amiga (pin 10) and connect that to pin 13 (Hsync) on the VGA-input of GBS, or if using the P11 connector the pin marked S or HS (two middle pins of p11), they all share the same trace if you flip the card you can visually observe that too. You can also check for continuity with a multimeter. It is also recommended to put a resistor in line with the Csync wire since Amiga is TTL-levels. Check Stedys pic here:

https://ianstedman.files.wordpress.c...82xx-cable.jpg

And you can mod your card with custom firmware (gbs-control) to get a much better picture quality, more relaxed timings on the RAM, insert scanlines etc. Check the shmups forum...Just a heads up, don't do the copper tape trick if going gbs-control.

[tpgb12]

Yes, the VGA output is still 15khz, but shouldn't the GBS just be able to convert that to 31khz so I can use it with any normal VGA monitor if I break up that VGA signal into the individual RGB components? It makes me think I may be doing something wrong if my PC-98 also won't work by doing this, although that's 24khz instead of 15khz.

And a side note, I have a Tatung CM-14SBM CRT and it's the only monitor I have where it almost displays my Amiga 500. Sadly, the image is really stretched and overlaps in the middle. The monitor has no horizontal size adjustment, so that's a shame. I think it's because it's probably not a true multisync monitor.

[jbilander]

Originally Posted by tpgb12

Yes, the VGA output is still 15khz, but shouldn't the GBS just be able to convert that to 31khz so I can use it with any normal VGA monitor...

Stock firmware does it with RGBS signal, not sure about RGBHV at 15 kHz. What you have read here on the forum, that it only takes 31kHz on RGBHV input, may be correct. Don't know, but try RGBS that I know should work.

[tpgb12]

Originally Posted by jbilander

Stock firmware does it with RGBS signal, not sure about RGBHV at 15 kHz. What you have read here on the forum, that it only takes 31kHz on RGBHV input, may be correct. Don't know, but try RGBS that I know should work.

I said earlier that the GBS' VGA input only does 31khz, so I'm not using that and instead using the port that's just above it (and not to the left since the gbs never came with a cable for that). I know that has to work with 15khz because that's what my supergun does and that works fine. Pretty sure that's the RGBS.

[jbilander]

It doesn't matter if you use the 8-pin or the 15-pin connector, they both take RGBS.




It is a matter of wiring pin 10 from the Amiga to either Csync input (S) or Hsync (HS) on the GBS.

Check this vid at around 3:20
[ Show youtube player ]

[DaIceMan]

Remember to add in series to the CSYNC output a 680Ohm resistor to bring the Voltage level down to the correct range to avoid possibly damaging the input. See:

https://ianstedman.wordpress.com/gbs-82xx-experiments/

Without it it still works however you are exceeding the specified input V range.

[tpgb12]

Alright, I know I've wired the Hsync/Csync to the correct pin and when I plug it in before turning on the Amiga it makes my power light flash. If it plug it in after it's powered up it just gives me a green screen. Unscrewing the Hsync connection allows the Amiga to power up fine, but of course you get no image...

I would just do a straight up DB23 to RGB instead of DB23 to VGA and then RGB, but unused DB23 female connectors are a delicacy, it seems.

[jbilander]

A standard DB23->VGA adapter doesn't have Csync (pin 10) connected to any of the 15 pins (DE-15 connector) inside the adaptor. It only has separate sync pin 11 and 12 wired. What you want for RGBS to work is Csync to the GBS pin (S) or (HS).

10 /CSYNC (Composite Sync)
11 /HSYNC (Horizontal Sync)
12 /VSYNC (Vertical Sync)

Yes DB23's are rare, what people often do now is buy a cheap DB25 and cut it down to a 23 with a hacksaw.