Sync stripper for SCART->VGA (projectors etc. only!) with EL4581

By Wild_Penguin

Hero (538)

Wild_Penguin's picture

21-03-2019, 14:50

Hi all!

I've been forced to do MSXing recently only on my OCM, or use composite video, since I sold my TVs and have nothing which can accept SCART RGB at the moment. My projector does have a VGA connector, and I know that projectors often can sync with composite video sync, or with sync cleaner / higher sync signal levels, works fine with 15kHz range (contrary to VGA monitors).

So I build a sync stripper (link1) - except, instead of LM1881 I used EL4581. The circuit works fine, with my NMS8255 and AX350-II. So, in case you have a projector (or similar device which can accept 15kHz signals) I can recommend building one Hannibal .

The EL4581 does not accept 12V, however, according to it's spec (link2) - max is 7v. The lm1881 accepts up to 12v (link 3). Sone instructions use pin8 for powering the LM1881. But most MSXes output 12V at this pin, as this is used to signal the display about aspect ratio (lower, 5-7V is for 16:9, and higher for 4:3 - and all MSXes are supposed to be viewed on 4:3).

So, two options remained: 1) use external power or 2) use regulator.

I tried first with external PSU, but decided it's too much of a cludge.... so after some consultation of a more able electrician, and remembering I have some SMD 5V regulators - a regulator and an extra capacitor on it's input was added. The final result looks like this:


Just one question remains. On HB-75P the RGB picture is slightly blue/purple -tinted. Curiously, the projector was also able to sync to the HB-75P even without any kind of conversion - but not reliably (whereas, the projector could not sync with my AX-350II not NMS). So I believe my particular projector has more problems with sync levels (or lack of vertical sync) instead of composite picture being mixed with the sync data, and something being off with the levels the HB-75P is outputting.

If someone who owns an HB-75P is reading this, any ideas are welcome! There's also the possibility that some components on the HB-75P are damaged, as it used to have some blown capacitors on the PSU side when I got it.

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By Wild_Penguin

Hero (538)

Wild_Penguin's picture

21-03-2019, 19:16

Hmm,

I noticed by accidentally not having SCART all the way in, I get decent blacks without blue. Inserting the cable more the blue tint is there again. Then I searched "HB-75P rgb blue" and it came up with this: HB-75p blue color . So there's something to try when I have time to open up the HB-75P. Thanks to lord_zett in case it works (will try to remember to report here if it does).

Just noting this here in case someone else comes here by searching for blue-tinted RGB....

(curiously, IIRC composite is fine or at least not so gravely blue as RGB output)