Z84C0020 - Will 20Mhz clock down in ZX Spectrum?

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Z84C0020 - Will 20Mhz clock down in ZX Spectrum?

Postby kevman3d on Sun Jul 07, 2013 9:12 pm

I suspect that it may be possible I need to replace the CPU (I'm just getting all kinds of advice now on fixing Speccies - a similiar problem with my older one (garbage screen) turned out to be a Z80 failure). The problem is that I've managed to find very cheap replacements, but they're newer versions that run up to 20Mhz versions... Can anybody here confirm that a processor like this will clock down to the lower speed if its used? I'd hate to try replace something just to see it go "pop" or make the machine unstable.

Just thought I'd ask.

Meanwhile, I've gone and ordered some replacement ram chips - the other machines' problem (according to various online sources) is possibly faulty upper ram... The white border and black paper... At the moment it feels like a guessing game, but I'll try one or two things using various online guidance that are relatively low cost and easy to try with my limited knowledge first. Hmmmmm.... :|
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Re: Z84C0020 - Will 20Mhz clock down in ZX Spectrum?

Postby TRS80 on Mon Jul 08, 2013 8:39 am

That will work fine if they are the cheap EBay parts out of China. I have some that I run at just over 7mhz in the home made Z80 machine and they work well. The frequency for the machine depends on the clock oscillator. The CPU rating is just the specified maximum clocking frequency for the part.

There have been comments in other places that these may not actually be 20mhz parts but they should be fine in a Spectrum.
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Re: Z84C0020 - Will 20Mhz clock down in ZX Spectrum?

Postby kevman3d on Mon Jul 08, 2013 8:45 pm

Great! Thanks for the confirmation... I ordered a couple from eBay (at $1.90 each, its not like breaking the bank), as well as a handful of 7805's (which were also like under $2 for 5) since they had free shipping (and were extremely cheap)

Talking regulators, a very nice guy put together a video on testing the regulator for noobs like myself after I pestered him on Facebook. :lol: He's got a pretty fun collection of videos on his channel ("Mark Fixes Stuff") - well, except the annoying heavy metal voice at the start of each one... :D
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