MSX hardware fixes and enhancements

How to fix some flaws in many MSX models

The MSX are great machines. But still, some of them had some design mistakes here and there. This page shows quick DIY guides so you can fix/improve your favorite model.

Disclaimer: There's no guarantee and I won't be responsible for any damage to your equipment. Do any of the fixes published here by your own choice and at your own risk.

General tips:

1) Explanation of the most common design mistakes fixed here

1.1) Sound Fixes:

There were two common mistakes in the sound circuitry of MSX computers:
Once the machine is fixed, test it with your favorite SCC+PSG and specially the FM+PSG songs (i.e.: Microcabin). All the accords will match perfectly, the sound will now be sharp and rich, and the bass frequencies will be full.

1.2) Jailbars

Jail bars are a common type o artifact that appears on video of many machines designed in the 80s. It's present on many video-game consoles like the Megadrive, Master System, SNES and also on the MSX.

2) DIY fixes per machine

2.1) Sanyo PHC-70FD and PHC-70FD2

This recipe fixes the following problems in this machine's sound circuitry:
Now, the fix itself. First, replace the following resistors and capacitors with new ones with the following values:
Then a small mod in the IC117 opamp is required to enhance the SNR and the final audio output volume:
PHC-70FD soundfix IC117 cut track location
PHC-70FD soundfix IC117 new resistors

The special thanks for this fix go to:

2.2) Panasonic MSX Turbo-Rs: FS-A1ST and FS-A1GT audio fix

The two Panasonic MSX Turbo-Rs have a very good audio circuit design that has everything it should have for its price range. But the result was poor because the circuit was terribly calibrated, resulting amongst other problems, in:
This fix recalibrates the audio circuit for maximum performance, and what astonishing difference that it does. It then blows any other MSX sound quality out of the water. It corrects all these problems, and normalizes the mixing volume between the slots (usually SCC or MSX-Audio), PSG and OPLL, to match the levels of the Panasonic MSX2+ and Sony MSX2+ machines. All filtering of the circuit is calibrated with the same parameters used in the famous high-end Yamaha SFG-05 module.

Here's the recipe:

a) FS-A1ST
    C48 = 1n8/50V polyphenylene sulfide or C0G ceramic
    C49 = 1n8/50V polyphenylene sulfide or C0G ceramic
    R24 = 22K
    R23 = 15K
    C57 = 180pF/50V polyphenylene sulfide or C0G ceramic
    C159 = 150pF/50V polyphenylene sulfide or C0G ceramic

b) FS-A1GT
    C17 = 1n8/50V polyphenylene sulfide or C0G ceramic
    C18 = 1n8/50V polyphenylene sulfide or C0G ceramic
    R50 = 22K
    R47 = 15K
    R55 = 47K
    C51 = 180pF/50V polyphenylene sulfide or C0G ceramic
    C45 = 150pF/50V polyphenylene sulfide or C0G ceramic


The special thanks for this fix go to:

2.3) Panasonic FS-A1GT jailbar fix

This machine has a design mistake that causes a very noticeable jailbar effect on its RGB output. Fortunately, it's very easy to fix.

This fix gives you three advantages:

On the motherboard, there look for a pair of jumpers called J1 and J2. Use the picture below as a reference:

Location of the FS-A1GT CVBS/CSYNC jumpers

These jumpers select whether CVBS or CSYNC will be sent to the DIN9 RGB output connector. By default CVBS is selected. But this signal contains a high frequency color carrier that shows up in most monitors as jailbars.  Thankfully, the CSYNC signal is clean and it's also a more adequate signal to be sent to the DIN9, as it will match the pinout of the A1ST and all the MSX2+ models.

So, to fix the problem, just cut the J2 jumper open and solder a drop of solder tin to close the J1 jumper.

But this also means you won't have CVBS (aka composite video) from the DIN9 connector anymore. This can be easily solved with a different break-out cable. Until now, you had to use a DIN9 -> CVBS breakout cable. From now on, you just have to use an S-Video -> CVBS breakout cable. I wonder why the Panasonic engineers just didn't use this solution from the beginning, instead of having modified the DIN9 pinout and created incompatibilities.

Build the the S-Video to CVBS breakout cable like this:

S-Video to CVBS breakout cable

The special thanks for this fix go to:

2.4) Philips NMS-8250, NMS-8255 and NMS-8280

This sound circuit is just unbelievably broken by design. It's the worst I have ever seen.

The circuit design seems to have been reused from an earlier cheap MSX1 machine, but then the engineer moved the amplifier section to the wrong place (only for the PSG line, that is usually louder than the other sources), and ruined for once what already wasn't exactly a great design.

IOW, the circuit only works properly for the internal PSG and you're lucky if anything else connected to the slot produces any sound. And I wouldn't recommend to connect two sound cartridges at the same time to these machines, because it short-circuits their sound outputs.

The RetroMSX page has a good fix created by Aquijacks, that copies the circuit from the NMS-8245 and fixes the circuit of the NMS-8250/8255/8280. The document is in Spanish, but Google Translate can help you with that.