Zeddy displaying wrong characters on screen

[Lardo Boffin]

I got a zeddy and it does this:

https://www.sinclairzxworld.com/viewtop ... 578#p54578

When you type using either the built in keyboard or my Memotech keyboard it does not show all of the characters you are typing correctly.

If I connect a Spand or a 16K memopak after a very short while it works fine. It starts out showing some characters slightly incorrectly but then they fully form.

Given that the Spand effectively replaces the ROM and RAM I have replaced both of these but it makes no difference.

[Lardo Boffin]

The fact that it also works with a 16K ram pack but not without would point to the RAM being faulty somehow but replacing it made no difference.

[Lardo Boffin]

This is what I get when I type all of the keys:

[msknight]

Nothing stuck in the keyboard sockets are there? Have you tried removing the keyboard and just using the memotech?

[Lardo Boffin]

I will check inside the keyboard sockets just in case but it does the same with just the Memotech keyboard connected.

It loads and plays the games that I have tried. Although the screen is suitably garbled.

[1024MAK]

Don't forget, with 16K bytes of RAM, you get a fully expanded display file, and it can be in a different position in RAM.

Have you tried changing the ULA?

Mark

[GCHarder]

I recall, along time ago, that I had a similar problem and replacing the voltage regulator fixed the problem. I got this idea from a forum posting but I can't find it. Not being a hardware guy I have no idea why the voltage regulator would garble the display, but replacing it worked for me.

Regards from Hardware Challenged;

Greg

[Lardo Boffin]

Don't forget, with 16K bytes of RAM, you get a fully expanded display file, and it can be in a different position in RAM.

Have you tried changing the ULA?

Mark

I will be looking for a spare later on thanks.

If I type in a program that takes up most of the 1K and it doesn’t corrupt would that prove the RAM is ok?

I did replace the 1K RAM with chips that were working a while back but this is the only socketed zeddy I currently have.

[msknight]

I'm taking that it came to you like this, and has never worked. Yes?

If that's the case, first thing would be to check for shorts and breaks on the data lines. But I take it you've already done this.

[Lardo Boffin]

It arrived like this yesterday. Sold as untested (as usual).

I haven’t had time to get technical yet - just a few minutes to try some high level stuff at lunch time.

Hopefully when the kids are in bed…