Problem with MSX VHD

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Por sd_snatcher

Prophet (3517)

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13-03-2020, 22:53

mars2000you wrote:

Little remark: the Victor HC-7 does not need the HC-A602S module as it has internal superimposing features. This module is only for the HC-5, HC-6 and HC-60 computers.

Yes. I think that the schematic only meant that the HC-A602S module is internal to the Victor HC-7. And judging by the following picture of the HC-7GB mobo, I suspect that it's present on that machine too, and it's the EA-6200A daughterboard.


We now have the following two possibilities:

1) The HC-7 can only work in composite-video mode while doing superimposing.

2) The HC-7 can decode the composite-video from the VHD player, superimpose it and output both via RGB and Monitor/VTR connectors

So, for a 1st test, let's try the following:

a) Build yourself a Monitor/VTR output breakout cable. I recommend making a short cable with female RCA connectors, as this makes your life easier because you can connect any standard A/V cables to it. Then connect this output to your CRT A/V RCA input.

b) Open one side of your RGB21 cable make a breakout input from there. Solder RCA female cables for the composite-video, audio R and audio L inputs. Be vary careful to use the correct input pins and not the outputs. Then, use normal A/V cables to connect these inputs to the VHD-player A/V outputs.

c) Test first in composite-video mode. Check if the image shows up correctly superimposed on the A/V input of your CRT.

d) Then, test it in RGB mode. Check if the image shows up correctly superimposed on the RGB input of your CRT.

If the (d) test doesn't work, the HC-7 can only superimpose over composite-video. Then I'll recommend that you build yourself a separate short composite-input RGB21 breakout cable, with female RCA connectors. And remove the RCA inputs from your old RGB21 RGB-only cable.

If (d) test does work, the it's proven that the HC-7 can superimpose on RGB mode and your Monitor/VTR cable won't be necessary anymore. It will be enough if you keep the RGB-21 cable with both RGB output and composite-video input.

Por gabbafiend

Supporter (6)

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14-03-2020, 13:05

Once again thank you to all for the responses!

sd_snatcher: I much appreciate the in depth comment! I'll definitely go with your suggestions.

It'll probably take a bit to get the cable. In any case I'll keep you updated.

Por italiandoh

Supporter (3)

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29-04-2020, 00:23

I've put together the whole setup many years ago with my friend Daniele, who is the owner of the system and still has it to this day. Here's a video of one of the games: Star Arthur Legend - Planet Mephius gameplay (MSX VHD interactive game)
The MSX Victor computer has built in superimpose feature. You need a special SCART cable to enable that and see the superimposed images on a TV, via RGB SCART. It took a while to us to figure out the correct way to interface it to achieve the superimpose feature.
The SCART output pinout of the computer is the following, from my notes of those days:

Measured from the Japanese MSX Victor HC-7.

1 audio ?
2 audio ?
5 ?
6 audio ?
9 ?
10 sync
11 +5V
12 ?
13 GND
14 GND
15 red
16 +3V (RGB ON switch)
17 GND
18 GND
19 green
20 blue
21 shield

You need to route the pins to the matching pin of the standard euro SCART connector. My friend Daniele has the cable we built and can provide pics (maybe, if he read this).

EDIT: found the manual source pic ->

Por gabbafiend

Supporter (6)

imagem de gabbafiend

09-06-2020, 19:29

Thanks a lot to Italiandoh for clarifying how to make the superimposse feature work on a RGB capable CRT! Many thanks as well for the pinout overview, the video and the image of the manual! This is of great help. Is there any chance that your friend Daniele could provide a picture of the cable?

sd_snatcher, thank you very much again for the approach you suggested! I tried it but it didn’t work as anticipated unfortunately.

My apologies for responding so late to your comments. I was a bit occupied over the last weeks.

Since the last time I posted in this thread, I got the chance to exchange with someone from Japan with some knowledge on the topic and also got a look at some old Japanese home computer magazines from around the time when MSX - VHD was made. From what I understand, (unless you use the method from Italiandoh) only a very limited number of CRTs are able to bring the signals of the MSX and VHD player together properly. It seems that by default most CRTs – even when both RGB and cinch connectors exist – can’t be used for displaying MSX and VHD signals at the same time. My Sony RGB monitors from the 1990s definitely won’t display the superimpose feature as intended. The only CRTs I know which can be used without modifications are the Victor AV-MT15 and AV-MT21. These CRTs were produced around 1983/84 and are next to impossible to find these days. So I was really glad when I read that Italiendoh found another way. Smile

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