Re: Failing I/O chips damaging each other?

From: Gerrit Heitsch <>
Date: Tue, 5 Apr 2016 18:58:16 +0200
Message-ID: <>
On 04/05/2016 06:11 PM, Rob Clarke wrote:
> Hello gentlemen,
> While investigating 3 failed 1551 drives, I found that in two of them
> both the 6523T and the 6525 in the drive were both defective. This I
> could understand in the case of spikes, static, or careless hot-plugging
> of the peripherals. But given a failure mode where one of the peripheral
> chips fails due to old-age, are they likely to die shorting the I/O pin
> to Vcc or ground, and if so, would it be likely to damage the I/O port
> to which it's connected?

The usual way to damage the 1551 is to plug or unplug the paddle while 
the computer and/or the 1551 is running.

> Also, as both the 6525 in the 1551 and the 6523T in the paddle take
> their power separately, and one obviously has to be powered on before
> the other, is there any any specific risk with these chips receiving
> logical high or low signals on their ports without power being applied?

No, otherwise you'd have the same problem with a 1541 on the 

> (fixing the 1551 paddle I will necro post on the old 6523T replacement
> thread)

You can make a 6525A fit. Well... kinda. It will work, but it won't look 


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Received on 2016-04-05 17:01:01

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