About

It’s a well-known fact that certain MSX2/2+ computers have a so-called “HIC Board” - the special “Hybrid IC” daughterboard that is mounted onto the MSX computer’s motherboard and provides certain functionality. This functionality is as follows:

• converts RGBS signals to composite video
• pre-amplifies and buffers audio
• mutes audio at startup and on pause to prevent clicks
• mixes all audio inputs
• amplifies and buffers the cassette interface signals
• buffers cassette interface’s relay operations

This board is known to be installed in the following MSX computers:

• Sony HB-F1II
• Sony HB-F1XD
• Sony HB-F1XV
• Sony HB-F1XDJ
• Sony HB-F1XDmkII
• Panasonic FS-A1mkII
• Panasonic FS-A1F
• Kawai KMC-5000 (Panasonic FS-A1F OEM)

Normally, the board works just fine, but there’s a problem with 3 electrolytic capacitors - they leak and damage the board, sometimes beyond repair. Fixing the leaked boards is difficult as some components can separate from the corroded solder pads, some tracks can be corroded under the CXA chip resulting in the board’s malfunction.

The original HIC board’s schematics and layout can be found here: http://elec-junker-p2.blog.jp/MITSUMI%20EMC-NX0039_REV02_PU.pdf

HIC Board’s Redesign

Taking into account all the above listed problems, it was decided to clone the HIC board and at the same time add the following improvements:

• use a better and commonly available encoder chip CXA2075
• add s-video output capability
• try to get rid of the original 4069UBF chip’s dependency
• make the HIC board detachable

It was also desired to get rid of the 2 special components: IMN10 and FMW1, but they appeared to be still available for purchasing, so they remained on the redesigned board.

During the redesign there appeared a few problems. The 4069UBF chip from Toshiba was used by the original engineers as an amplifier, so the board’s audio and cassette interface operations were dependent on certain features of that chip. When trying to replace this chip with similar ones, for example 74LS04 or 74HCT04, the audio functionality was crippled. The only possible replacement appears to be 74HC04 with 68pF capacitor added between pins 3 and 7 (GND). See the “74hc04_fix.jpg” image in the Pics folder.

The optional resistor R35 should not be installed unless the cassette input circuit doesn’t work as desired.

Where to buy parts

At the time of this readme’s creation the parts are available from the following sellers:

• pin headers (male and female): https://www.aliexpress.com/item/4001122376295.html
• CXA2075 encoder: https://www.aliexpress.com/item/33020885081.html
• 4069UBF: https://www.aliexpress.com/item/1005002494421415.html
• 68uH inductor: https://www.aliexpress.com/item/1005002963165525.html
• LMV358M amplifier: https://www.aliexpress.com/item/4001116443945.html
• 68pF trim capacitor: https://www.aliexpress.com/item/4000222152928.html
• 2SA1037 transistor: https://www.aliexpress.com/item/1005002503421569.html
• 2SC2411 transistor: https://www.aliexpress.com/item/1005004568437670.html
• IMN10: https://www.aliexpress.com/item/1005004322498640.html
• FMW1: https://www.ebay.com/itm/325038640119 or from Wierzbowsky (RBSC)

The resistors and capacitors 0805 and 1210 form factor can be ordered from any reasonable seller.