Sinclair ZX80 / ZX81 / Z88 Forums

Moggy wrote:Could be a dirty edge connector or the xpand not fully seated.
I say this because the first spand I bought I fitted into a Memotech case which had the Velcro that Memotech supplied fitted to the pack and the rear of the zeddy. This meant that the spand stood off from the case slightly and during boot up I got speckles and artefacts.

Removal of the Velcro meant the spand pushed fully home and problem solved.

I have cleaned the edge connnector again using IPA just in case but it turns out my 16k memopak works fine.

I think it is seated fully - it won't go in any further.

I have also removed it from the memopak case as I have just got the ay board fitted.

Do you have plugged AY board, too ?
I think it could be too much heat for the regulator as well.
You could try to use a regulated 7.5V or at least 9V DC supply (with correct pin out, plus for tip and minus for ring).
As it takes 30 seconds or so it could be a bit overheat for the voltage regulator driving all these modules. I think the 16k ram pack is hungry, too.

Best would be to replace the voltage regulator against a switching one.
There are many threads here at the board about these pin compatible regulators.
Reducing input power to the regulator can help as well.

PokeMon wrote:Do you have plugged AY board, too ?
I think it could be too much heat for the regulator as well.
You could try to use a regulated 7.5V or at least 9V DC supply (with correct pin out, plus for tip and minus for ring).
As it takes 30 seconds or so it could be a bit overheat for the voltage regulator driving all these modules. I think the 16k ram pack is hungry, too.

Best would be to replace the voltage regulator against a switching one.
There are many threads here at the board about these pin compatible regulators.
Reducing input power to the regulator can help as well.

I was going to say I have had no problems running xpand and AY with a ZX80 supply (600ma not recommended I know) and have in the past had a second AY connected as well with no problems but I have just remembered that my 81 is mounted on open chassis with cooling fans for the chips and regulator so perhaps that makes a difference?

EDIT
These days I use switching 1.5 amp like Lardo.

PokeMon wrote:Do you have plugged AY board, too ?
I think it could be too much heat for the regulator as well.
You could try to use a regulated 7.5V or at least 9V DC supply (with correct pin out, plus for tip and minus for ring).
As it takes 30 seconds or so it could be a bit overheat for the voltage regulator driving all these modules. I think the 16k ram pack is hungry, too.

Best would be to replace the voltage regulator against a switching one.
There are many threads here at the board about these pin compatible regulators.
Reducing input power to the regulator can help as well.

The PSU I bought for the toastrack is 9V, 1.5a switching. I have a spectrum to ZX81 conversion cable which I use.

I have tried a few different PSUs and they all do the same so I guess it's internal?

Is there a difference when you open the ZX81, at least does it take longer to show the pixels when operated free air ?

What I mean is a REGULATED power supply with 9V DC which is quite different to the UNREGULATED Sinclair PSU. This is stated as 9V but give properly more than 12V depending on load. It is calculated to give at least 9V wit full load (1.4 or 2.1 A). The less load you have, the more the voltage is feeded into the voltage regulator.

It can be, that the voltage regulator itself is not reliable anymore. So maybe time to change this.

The more heat the voltage regulator gets, the more it is agened over the time.
Nobody knows if this system has been plugged in for weeks, months or years or be used in general as coffee heater.
Can be a bad production of voltage regulators as well.

PokeMon wrote:Is there a difference when you open the ZX81, at least does it take longer to show the pixels when operated free air?

It didn't take a noticeably longer time with the case open.

However when I blasted it with a 2 foot high tower fan the sparkly stopped. It came back shortly after I switched it off. And then went again once I reapplied the fan for a while.

Overheating seems to be the problem!

Maybe I need one of those high gaming PC water cooled systems?

I will look into changing the regulator but de-soldering components isn't something I have tried before. But then neither was soldering a few weeks ago.

Pictures of regulator to follow...

Regulator sat on top of my zeddy:-
Any ideas if that is the correct alignment for it or if not what should I do to identify it?

Many thanks! Noob electronics guy here... My degree was in process engineering - a made up course in the 80's I think.

Lardo

Yep, that's the correct orientation.

I've marked pin one on both, just maintain the same orientation when installing.

Thanks!

If it still "sparkles" after the fitting the recom, try applying something suitable metallic to draw heat out of the ULA. If that cures the sparkles, it'd be worth fitting a DIP40 heatsink which might prolong the ULA's life a bit.

If that is the case, PM me your address and I'll send one over, return the favour for the sideways ROM a bit