$28 Gonbes GBS8200 Scandoubler for use with Commodore Amiga

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While I probably would have preferred to order an Indivision ECS scan doubler, a really nice alternative is a Gonbes GBS8200 video converter off of ebay. I had bought version 2.0 sometime in 2010 or 2011, and could not make it work in any fashion. I think, at the time, the limitation was the ability to handle a combined horizontal and vertical (composite) sync signal at a low refresh rate ~15khz, like the Amiga puts out.

I decided to try a new version, version 4.0, from the first quarter of 2014. I bought this on ebay for $28.00 shipped which is an awesome deal. I received the board three days later in the mail, which is impressive for free shipping!

Here’s the ebay item number and description in the case where the number will change:

Genuine Gonbes GBS8200 CGA/EGA/YUV/RGB To VGA Arcade Game Video Converter Latest

Luckily, I already had “stock” at my house of DB23F connectors, and I’m glad I bought some extra when I did. It seems there are still some sources around (in mid-2015) for some connectors, although prices seem to be going up. Worst case, you could hack an existing cable, or buy a replacement video cable off ebay, and use that.

For pinouts, you only have to connect (5) wires to get this working:

DB23 pin to VGA converter wire color

3 to RED

4 to GREEN

5 to BLUE

10 to GRAY (Composite Sync signal)

16 to BLACK (GND)

When the video converter powers up, press DOWN/AUTO button to get the unit to sync up. You may need to modify the horizontal position(I needed X position: 57) or adjust the zoom.

My unit powered up in Chinese. You need to select option 4 (bottom option) for language, and then choose English on the next menu.

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I powered this with my Rigol DP832 power supply and measured the current draw at various voltages. Note that you should NOT power this thing off of the Amiga’s DB23 video port. It simply can’t support the current draw.

Current draw in idle mode(no video): uses about 1.6 watts or +12v 133ma, +8.5v 180ma, +5v 300ma

Current Draw in active mode: uses about 2.4 watts or +12v 200ma, +8.5v 276ma, +5v 468ma.

So if you use a +5v regulated power supply, you need to be at least 625ma if you wanted a 25% safety margin. A 1 amp supply would probably be better. Note that the official specs call for 2 amps of current at +5v. My field testing doesn’t really prove that number out. I’ll keep it running for awhile, maybe something goofy happens like as it heats up, it draws more current, or something.

This blog here helped me, but remember, it’s not safe to power it off the video port!

Update: I’ve tested this on two different models, a Widescreen Samsung S22C300 monitor, and an older square Samsung SyncMaster 204B.

About the author

keith

Amateur Electronics Design Engineer and Hacker