PCW 8256 Problems

[The G Man]

Firstly a big hello to everyone here!  There do not seem to be too many sources of information on PCWs around so I'm glad I found this site.

Anyway, down to business.

I recently bought a PCW 8256 and after having worked fine for a few weeks it is now showing signs of a fault or two.  It will boot fine from either the CP/M disk or Locoscript and will work OK for a limited time, and then one of two things will happen:

The screen display will become corrupted and the computer will freeze and need powering off.

Or

It will detect multiple key presses and after a short time begin beeping continuously.  Unplugging the keyboard then reconnecting seems to stop this for a time.  However, it doesn't appear to be an actual problem with the keyboard as repeated characters (usually the letter "Z" but not always) will also appear on screen if I run CP/M with the keyboard disconnected.

If anyone has any idea what would cause these issues I'd be grateful for the help.  I'm fine with soldering / de-soldering components if need be but my only testing equipment is a multimeter.

[JonB]

The first thing to try is to reseat any socketed chips on the main board.

[The G Man]

The first thing to try is to reseat any socketed chips on the main board.

Thanks for suggestion.  I forgot to mention I have already tried reseating the few socketed chips on the board with no success.  Is there a particular chip that is likely to cause such an issue that you know of?

[JonB]

None in particular. You'll have to wait until someone more familiar with the hardware comes along, I'm afraid.

Interesting.. maybe your PSU is failing after getting warm. If you reset the machine (press Shift-Extra-Exit) does it continue doing it? What about when you power cycle?

[The G Man]

When I have the corrupted screen issue all I can do is power off - Shit-Extra-Exit will not work.  I can reset in this way if I have the repeated key press problem however.  Either way, after resetting or power cycling one of the two problems will occur again shortly - sometimes immediately, sometimes as much as 10 minutes later!!

[Token]

Maybe it worth a test on the 5V line with the multimeter.

On the mainboard:

° ° °  ° °
1 2 3 4 5
      AMSTRAD
         1985
1:DV
2:DV << GND
3:5V  << 5V
4:12V
5:24V

[Bryce]

A few things could cause this to happen. Bad capacitors. A chip getting too hot. A dry joint. So...

- Check the entire PCB for dry joints.
- Check if any chips are getting extremely hot.
- Replace the electrolytic capacitors.

Bryce.

[The G Man]

Thanks for the suggestions.  I'll look into it further when I get the chance