zondag 24 september 2017

Toshiba HX 10 MSX

The HX-10 was one of the first MSX computers to be introduced in Europe. MSX computers were the final initiative to get to a universal 8-bit computer platform. These Z80 based units were all equipped with Microsoft Basic. And just to illustrate that the HX-10 is really one of the first: it  contains version 1.0.

This unit was sold for a decent price (€20,-),but with the warning that some keys did not work. I expected that some cleaning might solve this problem, but when I tried the unit I found that Q, 3, R,F and V keys don't work. Since they are all close together on the keyboard it is more likely that something is wrong in the connections of the keyboard matrix. To my surprise there does not seem to be a 'Service Manual' or even schematics for the HX10 available online, so I'll have to figure it out myself.

Opening the unit is easy: there are only two screws left, the other four seem 'missing in action'. The keyboard is a very decent and sturdy construction. The key numbers are printed on the rear of the PCB so it's also very easy to find the location of the failing ones.

First I measured on a working key (the Esc key) how the keys are actually connected.
So top two and bottom two contacts are connected, and the switch connects bottom to top.
As with all keyboards from this era it must be some matrix. On the lower left side there are two connectors, a 9 and an 11 pin which are most likely the row and column connections. So I used the multimeter to check which keys each contact was connected to, which soon led to the following schema:

Key Numbers
1 0 1 2 3 [3] 4 5 6 7
2 10 11 12 13 14 15 16 17
3 20 21 22 23-. 24 25 26 27
4 30 31 32 33[F] 34 35 36 37
5 40 41 42 43[N] 44 45 46[Q] 47[R]
6 50 51 52 53[V] 54 55 56 57-[Z]
7 60 61 62 63[Caps] 64 65 66 67
8 70 71 72 73 74 75 76 77
9 80 81 82 83 84 85 86 87

The key numbers that have a letter next to them are the ones that do not work. From this I can see it's not a complete row or column that is missing, but just some section of a row. Closer inspection reveals that it indeed comes down to some broken traces.
So after adding just three wires, all contacts seem fine, and indeed the keyboard is working fine now.

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