Amstrad Mega PC vs Extron DVS 304 (finally using an ACV-011)

[Dioxaz]

tl;dr version: Only 256-pixel wide resolutions work and give a beautifully line-doubled image. 320-pixel ones won't sync ("NO SIGNAL" on the LCD panel of the Extron DVS). Syncs are combined with an Extron RGB device (any other solution for combining the syncs gives no picture with the DVS). Similar behaviour is observed with a Japanese Mega Drive with a French RGB cable using its "SYNC" signal rather than "COMP". PC part works regardless of resolution. Firmware on the Extron DVS 304 is version 1.15.

Original post: Hello everyone, I'm posting here as there seems to be some people who might be able to help me. I'm aware my post may look slightly outside what this forum is aiming for, but I didn't find any other appropriate places to post for the moment. I'm a proud owner of an Amstrad Mega PC since it was bought new in 1993 but don't have the original monitor in my possession anymore. For those who aren't aware of this machine, this is a hybrid with a PC part working at 31KHz+ and a Mega Drive part working at 15KHz both with RGBHV signals through its VGA port. Both parts are independent and cannot be used at the same time on its original unmodified design. The Mega Drive part works though an additional ISA card that routes its video signal to the VGA port with a ribbon cable.

It originally came with a dual-sync monitor able to display both 15KHz and 31KHz video. You all have guessed what I'm trying to do: line-doubling the signal of the Mega Drive part so it can be displayed on a 31Khz+ monitor.

I already tried a GBS-8220 but it didn't give me enough satisfaction because of its lack of precise adjustments. The picture it produces is also a bit blurry. It also lacks a pass-through mode and this forces to use multiple VGA switchers in order to have both PC and Mega Drive parts on the same monitor.

I also considered more expensive options such as XRGB devices but I wanted to see if I could get what I want with cheaper devices. The next option I'll try is a Wei-Ya ACV-011 (which is claimed as a pure line-doubler) which might look like the exact device I need.

For the moment, I'm left with an Extron DVS 304 which managed to give me excellent results on multiple devices except... this Amstrad Mega PC and a Japanese Mega Drive console (with a modified French RGB cable, which still use SYNC for its sync signal). I also have an Extron RGB 109xi for combining the syncs coming out of the Mega PC. I'm currently trying to figure out what causes the Extron DVS to fail syncing with the Mega Drive part of the Mega PC when it's fed with a 320x224 or 320x448 resolution but actually displays a nice image when fed with a 256x224 or 256x192 (SMS games) resolution (PC part works on the other hand, when using a TSR program forcing 15KHz output). I'm using INPUT 4 with the "RGBcvS" setting to get my picture (supposed to give SCART compatibility). The interesting thing is that if I select any other setting for that INPUT 4 (S-Video, Composite, YUVi notably), I actually get a very nice and working picture even for 320x modes. But obviously, no colour or wrong colours. Syncs are combined with another Extron, an RGB 109xi with ADSP disabled (no picture again if it's enabled).

Another interesting thing is that a Japanese Mega Drive with a modified French RGB cable yields the same results. This modified cable still uses the SYNC and not the COMP for its composite sync (Mega Drive consoles both output SYNC* and COMP* through their DIN socket). However, this guy on Youtube has successfully used an Extron DVS 304 with an European Mega Drive. I suspect his cable (he gives no info about what cable he's using) to use the COMP signal for its composite sync, which explains why he needs a Sync Strike.

* SYNC = clean composite sync
* COMP = sync on video composite signal (needs a Sync Strike or similar for some displays)

In the end, what could be causing the resulting composite sync of the Mega Drive part of the Amstrard Mega PC (through an Extron RGB) or a Mega Drive using SYNC to fail on the Extron DVS 304 whereas all other 15KHz displays in my possession (various TVs including a PVM-14L2) manage to display the picture perfectly? Are the sync pulses sent by the Mega Drive different from what they should be? Might a firmware update (which I'm unable to do as Extron won't grant me access to the firmware section of their site) possibly fix the issue? Asking just in case someone familiar with an Extron DVS and a Mega Drive might bring me some light. As said before, if the ACV-011 works, I'll put the Extron aside.

Additional details:

- the upscale is close to perfection when adjusting image size in "INPUT" settings and "PICTURE CONTROLS" and selecting 480p as "OUTPUT" resolution when the process works (slight colour bleeding and waving however and lag is around 1.5 frames)
- The Mega PC ISA card has been modified to output 60Hz as a 50Hz signal isn't treated as nicely on the DVS 304 (messes up the field order resulting in nasty combing while 60Hz is perfect)
- firmware on my DVS 304 unit is 1.15
- using an Extron RGB 109xi to combine syncs
- tried other methods of combining syncs (UMSA and self-made circuit) but results are worse (no picture at all in RGBcvS)
- tried the "RGB SCALED" setting on INPUT 4 but results in a glitchy mess (and scaling isn't as nice when it's working)

Thank you for reading in any case.

[Blair]

I'm a little out of my depth when it comes to sync issues but I'm wondering if the refresh rate is changing along with the resolution and that's what's causing the issues? also when it comes to your mega Drive RGB cable I know that specifications for NTSC RGB cables are a little different than European standards for those systems. is your mega Drive an actual NTSC mega Drive or is it a modified PAL system?

[Dioxaz]

Case closed? Almost. I just got my Wei-Ya ACV-011. I said after that one that I'd more or less give up. Well, I'm happy to report that the ACV-011 did indeed meet my expectations! More details here: https://www.reddit.com/r/crtgaming/comm ... cv011_win/

In short, it indeed line-doubles the output of the Mega Drive part perfectly and at all resolutions (256x, 320x and interlaced ones). However, the syncs still give some problems as the picture gets funnelled at the top and shifted to the right if selecting setting 16 on the dip switches (picture also disappear for short moments at random with this setting). The setting that worked the best in my case was the 14 (OOXO) according to the manual. It's an undocumented one but it gives the less distorted and most stable picture (still eaten up at the top).

Edit: I had the opportunity to test the unit in 50Hz too and I had slightly different results. Setting 14 gives me a truncated picture (not enough active lines) so I had to try setting 15 (OOOX) instead. Both 50Hz and 60Hz work with that setting but both also yield random picture drop-outs unfortunately. 60Hz in setting 15 shows garbage at the bottom because of too many active lines this time. So it's needed to correct the syncs coming out of the Mega PC in order to have flawless output for both 50 and 60Hz which would be friendlier with some scaling devices, line doublers and monitors. For now, if only using 60Hz, the ACV-011 in setting 14 is perfect (with some distortion at the top).

Edit 2 (2018-8-20): I also had the opportunity to try out other monitors and... got different results! I noticed the older the monitor the better it would sync to the line-doubled Mega PC signal. 2 monitors from circa 1991-1995 (a no-name HC-7423V and a Smile CL1515) got me a straight picture both from settings 14 and 15. But their lack of adjustability made me ditch them. All my more recent monitors (a Lite-On 17" and a Mitsubishi Diamond Plus 91 among them) gave me a blank picture. I also tried an Extron RGB 190 box at the end of my signal path, and got even more interesting results. I noticed that the picture with setting 15 on the ACV-011 was way too much shifted to the left. The CL1515 monitor didn't have enough range to adjust that. So I put my Extron inbetween and was able to reposition the picture. However, in the meantime I also decided to give my Sony Trinitron another chance with setting 15, and the Extron. And? Perfection has never been so close. Gone are annoying drop-outs and the picture is perfectly straight now. It looks like when DDSP is disabled on the Extron, not only you can adjust the H position but it also cleans up the sync pulses somewhat. When enabling DDSP, my drop-outs are back. Funny note, setting 14 is now unusable with the Extron added (jumping "Out of Range" message on the Trinitron).
In conclusion, the ACV-011 is a nice device but lacks H and V position settings and results will vary a lot depending on both your source and your monitor.

Otherwise, colours are vibrant (after adjusting the RGB pots), no bleeding, edges are crisp and sharp (but with some horizontal resizing artefacts), some interference may appear at times (especially on large solid colours areas) but the most impressive are: zero lag and no deinterlacing artefact whatsoever! The 2 strong points of this unit, whereas both the Gonbes and the Extron were showing deinterlacing artefacts with 240p material. Amusingly, when fed Sonic 2's interlaced mode, the unit only performs a stupid bob.

I'm really happy with this unit so far. Some sync-correction circuit might be needed in this case (which might also fix the issue with the Extron too), but this is enough for the moment. For the interested, the unit can be had for $50 with free shipping on Sintron ($65 as of February 2018).

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Previous post:

I thought about two things in fact: the sync pulses (their amplitude or length) or the vertical refresh rate. But for both 320 and 256 modes, the RGB 109xi reports a "59.3Hz" for the vertical frequency so I can't be really sure. Even though I doubt about the accuracy of that "59.3Hz" number coming out of the Mega PC, it might be possible that the system is really outputting 59.3Hz (when modified to 60Hz, as the ISA card originally outputs 50Hz).

The Mega Drive I used is a Japanese system (revision unknown, as I didn't take the system apart yet) so it's an NTSC one. The cable I'm using is the French RGB one, modified to fit any console (two resistors removed). Its composite sync still comes from the SYNC signal, not the COMP one.