Re: MFM drive gone nuts

From: Clockmeister <>
Date: Wed, 23 Jul 2014 07:03:10 +0800
Message-ID: <>
On 22/07/2014 5:02 PM, Michał Pleban wrote:
> Hello!
> Martin Hoffmann-Vetter wrote:
>> Is there a problem with the power supply? The hard drive use the +5V and +12V. The dynamic RAM uses only +5V. What happens with the +5V?
> I measured the voltage in the running system and both +5V and +12V
> voltages are good.
> On a side note: I replaced the failed TMS4256 chip with a stock 41256
> chip I had in my supplies, but it did not work. I thought all the x256
> DRAM chips should be interchangeable? Is there anything special about
> the TMS4256?

Both are 256kx1 chips with identical pinouts. Do you have another chip 
you can try?
44256 and 41256 chips are different, one is 256kx4 and the latter 
256kx1, but the datasheet suggest the 41256 should be compatible TMS4256 
unless the speed is an issue, which I doubt.

If you socketed the DRAM (sorry, I don't see all posts) check for shorts 
between pins that are side by side and then for continuity between pins 
of the other DRAM and one not working.

BTW, DRAM is sensitive to voltage, especially ripple, in my experience 
and a bad supply will kill DRAM even if the voltages read OK on a 

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Received on 2014-07-23 00:00:03

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