Re: Downright Criminal RAM

[Tristan Mumford <xtristan.xmumford@xgmail.xcom>]

 heuser.marcus@freenet.de wrote:

> On Sep 8, 11:20 am, Tristan Mumford <xtristan.xmumf...@xgmail.xcom>
> wrote:
>>
>> Besides that the power supply was reading erratic voltages.
>> Most notably on -5 and -12v.
>>
>> The 4116 RAMs use just about every voltage rail available. Both
>> positive an negative. Apart from possibly -12v. To be honest I
>> couldn't be bothered checking.
> 
> According to the Mostek datasheet the 4116 indeed uses +5V,
> -5V and +12V. The datasheet also says that the chip accepts
> tolerances of +/- 10%.

So if a rail were forcefed a vastly incorrect voltage with enough current it
would take them well outside the 10%

> 
>> One day during a poweron, or powercycle or something one
>> of the 4116 RAMs developed an internal short. They are quite
>> old after all.
> 
> Sounds possible.

The fragility of RAM in general is my bane.

> 
>> The shorting of the 4116 caused the internal potential of the other 4116
>> RAMs to change because of the clobbering / positive energising of the
>> negative rails (or it just shorted out into the address / databus). The
>> shift in voltages caused more to fail and so on.
> 
> Maybe. Did you try to pinpoint the damages chips?

I know it's a big maybe. It's unlikely but theoretically possible. And I
can't think of a better reason :)

I sure did try. The problem was the number of damaged chips seemed to be
increasing as I was testing.
They are all now sitting in an anti-static bag. I think I might do a
temporary uC rig to allow me to test them individually so I can find
remaining good ones.

Tristan.

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