CPCWiki forum

General Category => Amstrad CPC hardware => Topic started by: darkhalf on 16:58, 18 May 21

Title: Replacement Z80A CPU
Post by: darkhalf 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 (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
Title: Re: Replacement Z80A CPU
Post by: TotO 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...
Title: Re: Replacement Z80A CPU
Post by: darkhalf 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
Title: Re: Replacement Z80A CPU
Post by: RetroCPC 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...
Title: Re: Replacement Z80A CPU
Post by: TotO on 17:22, 19 May 21
Z0840004PSC

- 1x https://www.ebay.com/itm/174313284022?hash=item2895e1a1b6:g:Rz4AAOSwS7xe4eMj (https://www.ebay.com/itm/174313284022?hash=item2895e1a1b6:g:Rz4AAOSwS7xe4eMj)
- 5x https://www.ebay.com/itm/174313289653?hash=item2895e1b7b5:g:Rz4AAOSwS7xe4eMj (https://www.ebay.com/itm/174313289653?hash=item2895e1b7b5:g:Rz4AAOSwS7xe4eMj)
- 10x https://www.ebay.com/itm/392833995040?hash=item5b76bb1120:g:Rz4AAOSwS7xe4eMj (https://www.ebay.com/itm/392833995040?hash=item5b76bb1120:g:Rz4AAOSwS7xe4eMj)

Best price. Fee shipping, free return. Already ordered to this seller. Why searching another CPU version? :D
Title: Re: Replacement Z80A CPU
Post by: Bryce 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.
Title: Re: Replacement Z80A CPU
Post by: matburton 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?
Title: Re: Replacement Z80A CPU
Post by: TotO 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 (https://www.ebay.fr/itm/254599020800?hash=item3b4748c100:g:-DwAAOxy63FSvE2K)
Title: Re: Replacement Z80A CPU
Post by: matburton 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?
Title: Re: Replacement Z80A CPU
Post by: ajcasado 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.
Title: Re: Replacement Z80A CPU
Post by: TotO on 00:54, 12 November 21
Exactly.
Title: Re: Replacement Z80A CPU
Post by: VincentGR on 14:06, 12 November 21
Relentless also has problems with the other Z80, dunno if it is a 128K game though.
Title: Re: Replacement Z80A CPU
Post by: GUNHED 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?
Title: Re: Replacement Z80A CPU
Post by: ajcasado on 15:44, 12 November 21
I guess that is OUT (c),0, it outputs 0 in nmos and 255 in the cmos version.
Title: Re: Replacement Z80A CPU
Post by: GUNHED 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.
Title: Re: Replacement Z80A CPU
Post by: TotO on 18:17, 12 November 21
TFM knew it. :P
Title: Re: Replacement Z80A CPU
Post by: matburton 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)
Title: Re: Replacement Z80A CPU
Post by: Axelay 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.
Title: Re: Replacement Z80A CPU
Post by: GUNHED on 02:58, 14 November 21
TFM knew it. :P
Now  ;) :)
Title: Re: Replacement Z80A CPU
Post by: TotO on 04:26, 14 November 21
Now  ;) :)
"Oh crap! I didn't know!" Since January 2016 (https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/z80-cpu-nmos-or-cmos/msg116840/#msg116840)! ;)
Title: Re: Replacement Z80A CPU
Post by: GUNHED on 21:44, 14 November 21
"Oh crap! I didn't know!" Since January 2016 (https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/z80-cpu-nmos-or-cmos/msg116840/#msg116840)! ;)


Your memories are exzellent! Congratulations. I'm happy to know what I did last weekend.  :-\
Title: Re: Replacement Z80A CPU
Post by: TotO 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