Broken +3

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Lardo Boffin
Posts: 950
Joined: Sat Nov 26, 2016 2:42 am

Broken +3

Post by Lardo Boffin » Sun Jan 20, 2019 8:50 am

I have a +3 which is misbehaving.

It boots up ok and shows the usual menu screen (most of the time).

It refuses to recognise a working disc drive or gotek - it shows the drive as available but if you try to use it you get told to insert the disc. It does cat occasionally but if you try a second or third time it shows the insert disc error message.

If I connect a Retroleum Smart card it loads Manic Miner and runs it fine. If I try Exolon it hangs.

I ran the Smart card in diagnostic mode and got the following:-

CD8514A2-A822-4A61-A435-BF64BCFDBA27.jpeg

If I run the inbuilt diagnostics I get the following:-

74F18CC0-1C6C-40AD-BF1F-97487EA3CCC4.jpeg
Sometimes when I run the inbuilt diagnostics I just get a flashing screen (which apparently also signifies a RAM error).

So I changed IC3 and it made no difference. I guess I could change the others but not sure it would help.

Where next? RAM controller circuit? If the RAM is showing a problem but replacing the chips doesn’t help it I guess it would make sense that the controller is suspect.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

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1024MAK
Posts: 2370
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Broken +3

Post by 1024MAK » Sun Jan 20, 2019 10:30 am

The Amstrad gate array chip controls all the DRAM chips. If it’s this, that’s it, unless you can find a spare... (I don’t know of anyone who has spares).

So best concentrate on the DRAM chips.

However, you have renewed IC3 and it’s made no difference... :?

The schematic is here

Notice that there are four 4 bit by 64k DRAM chips. Two provide the 64k that is not contended, while the remaining two provide the contended RAM.

Mark

Lardo Boffin
Posts: 950
Joined: Sat Nov 26, 2016 2:42 am

Re: Broken +3

Post by Lardo Boffin » Sun Jan 20, 2019 10:41 am

Thanks, thats sounding fairly terminal then. :cry:
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

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1024MAK
Posts: 2370
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Broken +3

Post by 1024MAK » Sun Jan 20, 2019 10:45 am

Can you get to the “48k” mode by entering

Code: Select all

PRINT USR 0 
from 128k BASIC?

Mark

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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: Broken +3

Post by 1024MAK » Sun Jan 20, 2019 10:49 am

If yes, enter

Code: Select all

CLEAR 32000
You can then see if it will run in 16k “mode” where only the contended DRAM is used.

Most of the time, failure of this DRAM will result in some screen corruption.

Mark

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1024MAK
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Re: Broken +3

Post by 1024MAK » Sun Jan 20, 2019 10:53 am

Thinking about it, I’m sure that at least one intermittent fault has been reported where the gate array was suspected, but it was found to be a dry solder joint on one of the gate array pins. Worth checking.

Mark

Lardo Boffin
Posts: 950
Joined: Sat Nov 26, 2016 2:42 am

Re: Broken +3

Post by Lardo Boffin » Sat May 11, 2019 12:32 am

I eventually sent this off to be repaired. It turned out IC4 was faulty but my diagnostics software didn’t show it. Hey ho. Working nicely now thanks to Mutant Caterpillar Games. :D
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

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