Re: VIC-II DRAM refresh

From: Gerrit Heitsch <>
Date: Fri, 14 Oct 2016 09:54:38 +0200
Message-ID: <>
On 10/14/2016 09:39 AM, Francesco Messineo wrote:
> On Fri, Oct 14, 2016 at 9:34 AM, Gerrit Heitsch
> <> wrote:
>> Hm? They did use Micron DRAM, the dreaded MT4264-xx, in the C64 though. That
>> must have been a very early revision of the VIC2.
> what's wrong with the uT4264s (u as in greek mu)? I've seen them in
> many C64 boards but I don't think they failed more often than other
> brands.

But they do... You usually get the 'Out of memory in 0' message when you 
turn on the C64 plus some garbage characters on the screen. Or you get a 
blank screen. If you get the garbage, you can easily figure out which 
one of the RAMs is bad. There should be a SPACE, $20 there. Look up the 
screencode for the garbage char and see which bit different.

If you have a C64 with all MT4264-xx on it and one goes bad, it's a good 
idea to replace all of them, it's very likely that more will go bad soon.

I've had other DRAMs fail in the C64, but at least nowadays it's mostly 
the Microns when it's a bad RAM. And when I once bought half a kilo of 
mixed DRAM on ebay, most of the bad ones I foud when testing were 
Microns. Back then they worked, but it seems they don't age well.

As for the 'MT' or 'µT' on the Chip. To me it looks like a Mix between 
an 'M' and a 'µ'.


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Received on 2016-10-14 08:02:12

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