Broken +3

[Lardo Boffin]

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:-

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

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.

[1024MAK]

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]

Thanks, thats sounding fairly terminal then.

[1024MAK]

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

Code: Select all

PRINT USR 0 

from 128k BASIC?

Mark

[1024MAK]

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

[1024MAK]

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]

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.