MSX AX-200, power and keyboard issue..

Por Shinobi

Master (152)

Imagen del Shinobi

12-07-2021, 23:43

Hi ..

Lucky me!! today a friend gave me his old MSX AX-200 for free, it was in his house's store, so now I have two MSX AX-200, the first one that i made a keyboard for using Arduino and this second one.

After cleaning it from inside and outside, I turned it on, it didn't work, there was some issue in power cable, I fixed it. After that it usually turns on then shuts down and sometimes it stayed turned on for a long time. I checked the voltages, sometimes the power supply won't give 5 and 12 volts so that's why it turns off.
Can I use a 5 volt adapter to power the MSX?? like the one we use to charge our phones, or I need something with more power??

The second issue is with keyboard, it is very good except the "i" key always appears on screen like you're pressing the key, although the key from outside is ok, I will open the keyboard and clean it, any ideas??

Thanks

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Por Alexey

Guardian (3165)

Imagen del Alexey

13-07-2021, 10:42

Check the slot switches, they are common to cause problems as they may disable power supply.

Por Shinobi

Master (152)

Imagen del Shinobi

13-07-2021, 11:22

Should I get rid of the switches and short their wires??

Por Alexey

Guardian (3165)

Imagen del Alexey

13-07-2021, 15:31

Take them out of the slot's holder, put some WD-40 into them (after disconnecting computer from the mains of course) and trigger them manually 20-30 times. Then wait for the WD to dry and try powering up again.

Por Shinobi

Master (152)

Imagen del Shinobi

13-07-2021, 22:01

I cleaned these as you said, it resets but less times.
I cut the switches and shorted the cables, the machine resets but less than before.

Por Alexey

Guardian (3165)

Imagen del Alexey

13-07-2021, 23:16

Try a RAM expansion in slots 1 or 2. Does it reset with the RAM expansion? If not, then on-board RAM is faulty. Try running a diagnostics ROM (TESTRAM for example) and see if all tests pass. Try a RAM board from another computer and see if this helps against resets.

Take out the PSU and check if everything is still soldered well, if not, refresh the solder. See if any caps leaked, replace the leaked ones. Inspect the board for rust and pieces of solder - those may cause occasional reboots. Check the stability of clocks on VDP and CPU. Check if power fluctuates too much (over 500mV is already too much).

If you find the source of the problem, I recommend to put the switches back.

Por Shinobi

Master (152)

Imagen del Shinobi

14-07-2021, 00:22

I think it was the same problem as my other MSX AX-200, they both were abandoned for 20+ years, some chips become inactive in some way. my last MSX only read half of RAM only 16K, when I was checking the signals with continuity test from the MSX engine, I saw that there was some signals going into a logic IC then goes to RAM socket, after shorting it manually with a cable it worked, then after taking the cable out, the whole RAM was read..

In my new MSX, it is the same, at first it was main cable problem, fixed it, then it was turning on and off, I shorted the switches, it worked but resets sometimes, I knew it was a ram problem, so I began to load 16K games using cassette port, it worked, but loading 32k games didn't work for two times, after that it worked even loading some original 55k games.

When you leave electronics not used, some weird things happen, so now MSX is ON and I am checking it if it is resetting, till now it is ok for 1+ hours and loaded 4 games, everything is ok..

At least it's keyboard is working now and I don't need to make it a new keyboard..

Thanks Alexey