Amstrad 4128plus suspect ram....

[CraigsBar]

Hi all.

Please see the 'bugs' posted in the m4 thread for some issues my Bryce upgraded 464 plus is having....

I no longer think these are bugs as my 6128plus exhibits none of these problems with the exact same setup.

Now I suspect the ram is to blame but all ram test programs come back clean. Is there any pending fault or slow degradation of ram that would fool the test but messup in actual use?

Groops for example will only load the game successfully (the language selection and animated titlescreen are fine) after a cold boot. Once loaded it runs fine for as long as I want, but if I reset, or power off and on again it will crash/reset after the animation on the title screen completes.

I have some more new old stick NEC ram on the way, but is there anything else I should be looking at?

Craig.

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[luismcv]

You might want to try to swap the CPUs?

When I first received my M4 I was having frequent crashes with a 6128 that I had recently acquired. And if I tried to override the lower ROM the machine wouldn't even boot most of the times. After a lot of contacts cleaning, I decided to take my old 464 (that I had since I was a child) from storage and try with that one; it gave some issues at first but it worked perfectly after just some light contacts cleaning.

After a few emails to Duke, more contacts cleaning, voltages checks, even more contacts cleaning, and - just in case - some contacts cleaning to no avail, he suggested to swap the Z80s. And that worked. My 464 had a Zilog Z80, the 6128 a Mostek. The funny thing is that the Mostek still works perfectly fine with the M4 in the 464.

Because I had double-socketed the CPUs to make it easier to swap them again if needed, I tried to swap them several times to discard a bad contact or something like that and every single time I got the same results: the M4 & Mostek crashed in the 6128, but worked fine in the 464; and the 464 worked just fine with any of the CPUs.

So it'd seem that my Mostek Z80 might not be very tolerant to some timings, voltages or something that for any of the multiple possible reasons (capacitances in inputs or outputs, length of tracks, differences in specs or degradation of decoupling capacitors or who knows what) are different between my two CPCs.

It's easy to do so you don't lose much trying. The upgraded 464+ might keep failing, you might migrate the problem to the 6128+ or, if you're lucky like I was, completely get rid of it.

[arnoldemu]

mostek z80 seems a bit unusual for a cpc....
maybe it was repaired?

[Duke]

@CraigsBar

As I understand it, you only have problems when using CPC+ cart mode (|ctr), correct?
If everything else works fine, it's hardly the CPC+ at fault, more likely my cartridge emulation doesn't have correct timings, as was shown when using C4CPC and M4 with geralds rom tester.
So don't put too much in it if its only |CTR mode, it may not be perfect yet. I will get back to it.

[Kris]

For you information I have often found Mostek Z80 in CPCs, I have replaced most of them with Zilog ones since I got some issues with Mostek CPUs (remember post about Z80 tests results).

[CraigsBar]

@CraigsBar

As I understand it, you only have problems when using CPC+ cart mode (|ctr), correct?
If everything else works fine, it's hardly the CPC+ at fault, more likely my cartridge emulation doesn't have correct timings, as was shown when using C4CPC and M4 with geralds rom tester.
So don't put too much in it if its only |CTR mode, it may not be perfect yet. I will get back to it.

No. I am noticing more and more errors. Even with no expansions and loading from floppy. Groops for example only runs from a cold start after about 5 minutes power off. I don't therefore think it is either the m4 or the c4cpc more likely my machine. No ram is running hot. But then again it all passes ram tests too. Replacement NEC IC's are I expensive enough to be a first test.

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[CraigsBar]

For you information I have often found Mostek Z80 in CPCs, I have replaced most of them with Zilog ones since I got some issues with Mostek CPUs (remember post about Z80 tests results).

My plusses both have ST z80 chips. And one works, the other has issues. So I suspect it is not the CPU.

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[Bryce]

I hope the ASIC isn't starting to die!

Bryce.

[dragon]

MMM.  The amstrad is very old and can suffer from general electronics fault, not necesarily ics.


My last pc  power supply works perfect when i switch on the computer.But after reset it not boot until 20minutes later.


That i say, the cpc use capacitators,resistances etc.etc. And it can die after 27 years.


So if i was you i check the caps.

[CraigsBar]

I hope the ASIC isn't starting to die!

Bryce.

If it was asic I would expect an allways broken or nothing fault.

This is definitely varying!

Still hope the ram is to blame.

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[Duke]

Exact same setup, does that mean same powersupply aswell?

Also, I would try to exchange the Z80, because it's one of the few things that is very easy to do. I do not know if its common they fail, but I do have a faulty from 664, so I suppose it can happen.

[CraigsBar]

Yes, same cm14 for both machines. I do have a known good zilog z80 on the shelf so can swap that over tonight.

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[CraigsBar]

OK swapped the CPU. Although the zilog z80 works in both my cpc6128s it does not play ball in the 464plus. However I also wiggled the ram in the upper bank sockets and now groops seems to work every time

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[CraigsBar]

Will try disc to m4 file copies later and see what they go like.

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[CraigsBar]

Hmmm. OK znax still has visual corruption when copied from floppy to m8. Since a ram wiggle fixed it partially I hope a ram swap is all that is needed. Even if that means I need to remove and socket bank 1

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[luismcv]

mostek z80 seems a bit unusual for a cpc....
maybe it was repaired?

I don't know for sure. The 464 and I will be 30 years together this Christmas, but the 6128 I got from ebay last year. But if it's been repaired it must have been long time ago, because it came with the original gummy-mess drive belt that I had to clean away and replace.

Edit: In case you're curious, it's a MC0020F version, with serial 533-75x

[luismcv]

For you information I have often found Mostek Z80 in CPCs, I have replaced most of them with Zilog ones since I got some issues with Mostek CPUs (remember post about Z80 tests results).

I'm curious about the issues you had and the differences. I tried to find that post you mention, but a search for Mostek in the forum didn't return much. Will you happen to have a link at hand? Thanks.