Need help repairing Philips MSX2 NMS 8250

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By Manuel

Ascended (15620)

Manuel's picture

25-09-2018, 21:44

Can you hear the keyclick when typing characters? Does CAPS lock work on the keyboard?

By llopis

Rookie (32)

llopis's picture

25-09-2018, 21:50

luppie wrote:

When powering up the machine, do you hear a mechanical click (relais)?
Does the drive spin up when powering the machine?

I definitely hear the relay. I don't hear anything spinning up on the drive, but it doesn't have any disks in it (I don't have any).

By llopis

Rookie (32)

llopis's picture

25-09-2018, 21:55

Manuel wrote:

Can you hear the keyclick when typing characters? Does CAPS lock work on the keyboard?

No clicking at all (I didn't realize there was supposed to be clicking with every keypress).
I don't see any lights when I press CAPS (I assume it's the up arrow with a circle around it). The keyboard only has the "power" light on.

By Manuel

Ascended (15620)

Manuel's picture

25-09-2018, 22:03

llopis wrote:
Manuel wrote:

Can you hear the keyclick when typing characters? Does CAPS lock work on the keyboard?

No clicking at all (I didn't realize there was supposed to be clicking with every keypress).
I don't see any lights when I press CAPS (I assume it's the up arrow with a circle around it). The keyboard only has the "power" light on.

A power light on the keyboard? Are you sure? Where is that located?

By llopis

Rookie (32)

llopis's picture

25-09-2018, 22:24

Manuel wrote:

A power light on the keyboard? Are you sure? Where is that located?

It's the one towards the bottom. On that groove below the caps lock and space keys.

Is that supposed to be a CAPS LOCK indicator? Mine turns on as soon as I turn on the computer.

By Meits

Scribe (5460)

Meits's picture

25-09-2018, 23:12

It's the caps lock led indeed.
It should not turn on if you turn on your computer. Only when you press the caps button.

By Grauw

Ascended (8317)

Grauw's picture

26-09-2018, 00:28

Does not seem like a video RAM problem then. The computer should be able to boot (albeit with corrupted graphics) even if the video RAM is malfunctioning, you should be able to hear key clicks and toggle the caps lock. Other usual suspects are the RAM, the ROM (bitrots sometimes), and logic ICs. CPU / VDP / MSX-Engine malfunctions are less common (and in case of the engine, very difficult to source a replacement).

Whether the RAM is the problem can be tested by plugging in an external memory mapper, if the machine boots normally then it’s the RAM.

By Wild_Penguin

Hero (541)

Wild_Penguin's picture

26-09-2018, 08:48

The keyclick sound you get from pressing the keys is very faint. Be sure to turn the volume way up when looking for it. It is very easy to miss especially with a mechanical keyboard - press the keys slowly so the mechanical sound does not mask it! Big smile

By llopis

Rookie (32)

llopis's picture

26-09-2018, 08:59

Grauw wrote:

Whether the RAM is the problem can be tested by plugging in an external memory mapper, if the machine boots normally then it’s the RAM.

Is this a ROM I can burn and put instead of the existing ROMs, or are we talking about a cartridge?

Also, in a few days I should get a MegaFlashROM. Is that something I can use to try a test RAM program? Any recommendations for which one?

By Meits

Scribe (5460)

Meits's picture

26-09-2018, 11:27

Grauw's talking about a cartridge with just RAM and a memory mapper on it. Since the 8250 has its own RAM in slot 3 and you can put the cartridge in slot 1 or 2, your cartridge's ram will always be recognized first.
Saved me once. Good way to rule out RAM issues.

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