HIC-1 board redesign and improvement

Guardian (3649)

20-03-2021, 18:55

I am tired of fixing the broken and rotten HIC boards, so I decided to make my own based on the CXA2075M, 74HCT04 and LMV358M chips with the help of our electronics engineers. Some obsolete elements (FMW1 and IMN10) will be replaced with more commonly available parts. I don't yet understand the part where the CSYNC and VSYNC are somewhat mixed, sent to the CXA1145M and then the output is fed to CSYNC OUT. The missing OPAMP from CXA1145 will be replaced with a separate OPAMP (as a buffer).

The board will be 2-sided and it will have pads for S-Video output. The board will be NTSC only and will allow it to be mounted on the original pins as well as on the jumper pins. I will make the pads compatible for the pin headers.

I would appreciate any help in checking the schematics for possible problems. I haven't finished the OPAMP part yet, so this is still WIP.

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Van sdsnatcher73

Enlighted (4304)

20-03-2021, 20:06

Nice work! This will help recovery for many machines that time was not fortuitous upon.

Van alexito

Paladin (761)

20-03-2021, 22:04

Great news Alexey I got a SONY MSX 2 with the HIC video amp damaged this project will be great to revive my beauty.

Van meits

Scribe (6573)

20-03-2021, 22:07

Great initiative. That'll teach those decayed boards.

Van Wierzbowsky

Guardian (3649)

21-03-2021, 04:49

After an in-depth discussion with our engineer it became evident that without CXA1145 with its OPAMP and CSYNC normalizer it would be impossible to fit all replacement circuits onto the tiny 52x37mm board, even on both sides. And with the cloned board it would be impossible to get S-Video output from 1145 without additional parts. Bummer...

Van gdx

Enlighted (6438)

21-03-2021, 08:47

Nice initiative. S-Video in extra would have been useful but if it works like the original, that's fine. I already know someone interested in this board for a FS-A1. Do you plan to sell the board with the components soldered or a complete kit?

Van Tabajara-Labs

Expert (95)

21-03-2021, 09:02

People says that great minds think alike... =)
https://tabajara-labs.blogspot.com/2019/01/reforma-do-fs-a1-e-o-projeto-da-placa.html
Gotta finish this board :\
BTW, does anyone has a FS-A1F keyboard or membrane to sell? Lend mine to help a friend and now I'm keyboardless =)
(ok, I know, silver paint, etc)

Van Wierzbowsky

Guardian (3649)

21-03-2021, 17:26

Bravo, Alexandre! You made it to the working prototype already. I guess there's no point for me to continue the project in parallel. Just make sure that the original board's functionality is fully reproduced. You need to have the VSYNC extraction circuit, separate OPAMP and CSYNC normalizer (from 4.6v to 2.6v and 75 ohm-capable). You also need a proper YTRAP with a trim capacitor and a coil. The biggest challenge will be to fit all that on a small board and avoid interference.

Nice restoration project! Like in my Yamaha's restoration, there's always a side benefit, when something could be made better and used for other computers. Like the new HIC board...

Van Wierzbowsky

Guardian (3649)

04-10-2021, 03:59

I've made some progress

As the schematics has changed (new encoder chip + S-Video output), there's no guarantee that this board will work as expected once I assemble it. If someone wants to try to assemble it before I manage to do this myself, I could share Gerber files.

Van sdsnatcher73

Enlighted (4304)

04-10-2021, 06:20

Nice work Alexey! Some questions:

- I see you put Y0 and C0 pins in the top left corner but what is the original use of these pins?
- How does the audio mixer circuit compare to the original HIC board? Did you make any changes in this area? I suspect R27, C20, R33 and C23 (maybe just the latter two?) implement the low pass filter? What is the cut off frequency from these values and how does it compare to Yamaha SFG design which many soundfixes are based upon?
- The beep on most MSX2 (if you press ctrl+G) is often very low volume (much lower than most MSX1), is that due to the high value of 1M on R19? What would happen if this were a bit lower? Maybe the beep would be more audible? What else would be affected? Keyclick maybe?

Van Wierzbowsky

Guardian (3649)

04-10-2021, 10:34

- These YO and CO were not on the original board, these are for S-Video output. I also added GND pad there. The edges will not be drilled, just pads will be there to connect wires or solder a pin header
- The mixer circuit is unchanged (but see below)
- This board doesn't amplify anything, this is just a sound buffer, similar to what was in CXA1145, but is missing in CXA1645 and later encoders