Sinclair ZX80 / ZX81 / Z88 Forums

Hi all

I recently bought an issue two Spectrum in order to refurb so I had one I had done myself. It's all working fine on its own - loads games fine and the iPod turbo loader is an absolute revelation! Manic miner loading in 23 seconds!

But when I connect my DIVMMC future to it weird things happen! It insists on thinking I am constantly pressing the # key, but only when it warms up. It doesn't do it for the first 30 seconds. After this point it does it every second or two. If I manage to get a game loaded it then appears to be pressing other keys on my behalf - e.g. In Manic Miner the music switches off, it pauses, unpauses and jumps etc.
I have tried a few different membranes in case it is that. No difference. I have even tried it without a membrane and it still does it.
Without the DIVMMC plugged in all is well.
The DIVMMC works fine with my issue 4B.
Unfortunately I don't have another sd card reader to test with.
I have given the edge connectors a very good clean.

Any thoughts?

Many thanks!

Lardo

ULA.

Possible but less likely:
http://blog.tynemouthsoftware.co.uk/201 ... gnals.html

sirmorris wrote: ↑Wed Sep 27, 2017 10:51 am ULA.

Possible but less likely:
http://blog.tynemouthsoftware.co.uk/201 ... gnals.html

Thanks but I was hoping no one would say ULA...

The DIVMMC works ok apart from the random keypresses - I assume from the article that it would not work at all if the M1 line was dud?

That's my experience. No M1 = No work. I only mentioned the M1 line as it's my typical go-to.

As the problem gets worse with heat have you tried a freezer spray?

sirmorris wrote: ↑Wed Sep 27, 2017 12:12 pm That's my experience. No M1 = No work. I only mentioned the M1 line as it's my typical go-to.

As the problem gets worse with heat have you tried a freezer spray?

I don't have any freezer spray!

I will try a strong fan though - it may be sufficient to make a difference (it did on my sparkly pixel zeddy a while back).

Do you have an air duster can?
If yes, hold it upside down and carefully spray the air (which will come out as a mixture of air and cold fluid) on the centre of the chip. Watch that you don't get any in your eyes or on your skin though.

Mark

What board version is this Spectrum?

There is a design issue with the early boards that used the early ULA chips, in that the I/O port decoding does not work properly. The ULA then thinks any I/O operation is aimed at it...

Does the CPU have a transistor sat on top of it, or connected by a wire to one of the pins?
Or any extra resistors and diodes on top of the CPU, or nearby?

Mark

It's an issue two with an OKI RAM upgrade to 48K:-

I have asked Alex at Mutant Caterpillar Games if she will try to see if she gets the same with any issue twos her end.

My air duster can is empty! Argh. Time to order some more.

MCG have kindly tried an issue two with an OKI RAM upgrade and it does not have the same issue. Hmmm.

<cough> transistor on top of the processor <cough>