Author Topic: Replacement Z80A CPU  (Read 1772 times)

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Offline darkhalf

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Replacement Z80A CPU
« on: 16:58, 18 May 21 »
Unfortunately my recently aquired CPC464 will did not power on. Sometimes screen would scroll random patterns and then stop.


I swapped the Z80A over (from the other CPC464) and all came to life fortunately. Was hoping it wasn't one of the ASIC Amstrad parts!


So now I'm in the hunt for another Z80A. Do you need to use the Zilog ones or can the Sharp ones be used?

https://www.ebay.com.au/itm/372272867554


Does anyone know of a reliable source for these?


I'm in Australia, and freight is a nightmare 60GBP just to get the 464 here due from the UK. Many ebay sellers have complaints of counterfeit chips. I've seen this first hand with CRTC chips. Had one good one, and one fake


thanks
Matt
« Last Edit: 07:33, 19 May 21 by darkhalf »
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Offline TotO

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Re: Replacement Z80A CPU
« Reply #1 on: 17:05, 18 May 21 »
Use NMOS Z80 CPU to be fully compatible with CPC programs like Z0840004PSC.
I don't know about if the Sharp Z80 are NMOS or CMOS...
« Last Edit: 17:08, 18 May 21 by TotO »
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Offline darkhalf

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Re: Replacement Z80A CPU
« Reply #2 on: 00:36, 19 May 21 »
Okay thanks will dig further


Part number on working 464: MOSTEK MK3860N-4
Dead 464 and my working 6128: Zilog Z8400A PS (380A)


Edit: CPC service manual has IC111 as Z84400 APS
« Last Edit: 00:39, 19 May 21 by darkhalf »
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Offline RetroCPC

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Re: Replacement Z80A CPU
« Reply #3 on: 16:38, 19 May 21 »
Are you sure the Mostek part number is not MOSTEK MK3880N-4 ?

Anyway, this is a better link for a NMOS Z80A:-

https://www.ebay.com/itm/402782080514?hash=item5dc7aece02:g:-Y8AAOSwSddgbVrT

With ordering from China, you always have the risk of fake parts but the cost of this part its not going to break the bank...
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Offline TotO

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Re: Replacement Z80A CPU
« Reply #4 on: 17:22, 19 May 21 »
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Offline Bryce

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Re: Replacement Z80A CPU
« Reply #5 on: 17:36, 19 May 21 »
I've bought parts from them in the past too and they were always good. Now if I could just convince them to stop using that non-ESD safe pink foam they use, they would make it higher on my favourites list!

Bryce.
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Offline matburton

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Re: Replacement Z80A CPU
« Reply #6 on: 21:24, 11 November 21 »
Use NMOS Z80 CPU to be fully compatible with CPC programs like Z0840004PSC.

I've also had to replace a CPU (among other things) and bought a Z0840004PSC.

How can I check it's genuine, i.e. NMOS and not re-badged CMOS? Anything I can do at the basic prompt?
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Offline TotO

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Re: Replacement Z80A CPU
« Reply #7 on: 22:09, 11 November 21 »
How can I check it's genuine, i.e. NMOS and not re-badged CMOS? Anything I can do at the basic prompt?
I have bought them two times from this seller two years ago and they worked properly:
https://www.ebay.fr/itm/254599020800?hash=item3b4748c100:g:-DwAAOxy63FSvE2K
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Offline matburton

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Re: Replacement Z80A CPU
« Reply #8 on: 22:14, 11 November 21 »
I have bought them two times from this seller two years ago and they worked properly:

How did you know they were genuine NMOS? Were there any checks you performed?
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Offline ajcasado

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Re: Replacement Z80A CPU
« Reply #9 on: 22:29, 11 November 21 »
How did you know they were genuine NMOS? Were there any checks you performed?

Run any program that uses the Arkos sound engine (for instance adios a la casta), if the sound is OK then the CPU is NMOS. It uses undocumented opcodes that perform different actions in cmos and nmos z80's.
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Offline TotO

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Re: Replacement Z80A CPU
« Reply #10 on: 00:54, 12 November 21 »
Exactly.
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Offline VincentGR

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Re: Replacement Z80A CPU
« Reply #11 on: 14:06, 12 November 21 »
Relentless also has problems with the other Z80, dunno if it is a 128K game though.
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Offline GUNHED

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Re: Replacement Z80A CPU
« Reply #12 on: 14:51, 12 November 21 »
Run any program that uses the Arkos sound engine (for instance adios a la casta), if the sound is OK then the CPU is NMOS. It uses undocumented opcodes that perform different actions in cmos and nmos z80's.


Which Z80 commands / opcodes are the problematic ones?
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Offline ajcasado

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Re: Replacement Z80A CPU
« Reply #13 on: 15:44, 12 November 21 »
I guess that is OUT (c),0, it outputs 0 in nmos and 255 in the cmos version.
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Offline GUNHED

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Re: Replacement Z80A CPU
« Reply #14 on: 15:49, 12 November 21 »
I guess that is OUT (c),0, it outputs 0 in nmos and 255 in the cmos version.
Thank's a lot for that information. Well, I used that instruction too. Good to know in case of problems.
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Re: Replacement Z80A CPU
« Reply #15 on: 18:17, 12 November 21 »
TFM knew it. :P
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Offline matburton

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Re: Replacement Z80A CPU
« Reply #16 on: 18:21, 12 November 21 »
I guess that is OUT (c),0, it outputs 0 in nmos and 255 in the cmos version.

Long shot, but is there any way to try this Z80 instruction from basic?

I have a working keyboard but not a working tape drive for this CPC.(The idler tyre has perished)
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Offline Axelay

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Re: Replacement Z80A CPU
« Reply #17 on: 03:52, 13 November 21 »
Relentless also has problems with the other Z80, dunno if it is a 128K game though.


It's not 128k, only 64k required, was designed to fit in a 16k ROM for the wiki compo.  But it uses the Arkos Tracker 1 replayer, which does use that OUT (C),0 instruction.
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Offline GUNHED

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Re: Replacement Z80A CPU
« Reply #18 on: 02:58, 14 November 21 »
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Offline TotO

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Re: Replacement Z80A CPU
« Reply #19 on: 04:26, 14 November 21 »
Now  ;) :)
"Oh crap! I didn't know!" Since January 2016! ;)
« Last Edit: 04:31, 14 November 21 by TotO »
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Offline GUNHED

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Re: Replacement Z80A CPU
« Reply #20 on: 21:44, 14 November 21 »
"Oh crap! I didn't know!" Since January 2016! ;)


Your memories are exzellent! Congratulations. I'm happy to know what I did last weekend.  :-\
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Offline TotO

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Re: Replacement Z80A CPU
« Reply #21 on: 14:16, 15 November 21 »
Your memories are exzellent! Congratulations. I'm happy to know what I did last weekend.  :-\
Thank you, my own X-MEM. ;D 
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