powering up older machines - is it safe?

[Allison]

>
>Subject: Re: powering up older machines - is it safe?
>   From: ard at p850ug1.demon.co.uk (Tony Duell)
>   Date: Tue, 03 Jun 2008 04:39:09 +0100 (BST)
>     To: cctalk at classiccmp.org
>
>> > The main worry is not a capacitor Failing. The main worry IMHO is that if 
>> > there's a fault in the power supply regulation circuitry then that could 
>> > make the +5V line jump to a high enough voltage to wipe out just about 
>> > every chip in the machine. Expansive and difficult to put right.

However the  swithers used are less likely to overvolt than fry the
high voltage side (chopper fails!).   In the case of the Robin that
is there the risk is (other than the video board cap).

Allison

>> 
>> I don't disagree with the concern, but I'd be interested in hearing
>> estimates on the probability of this taking place.  Has anyone had it
>> happen to them?
>
>Yes, sort-of....
>
>I've never had it happen in a classic computer, but years ago I was 
>making a homebrew SC/MP machine. I'd obtained a surplus PSU which I'd 
>tested and worked fine, and then stuck on the shelf. I was foolish enough 
>to get it out a couple of mnths later and attempt to use it to power my 
>homebrew board. Alas something had failed in the PSU (I forget what, it 
>might just have been a dry joint...) the +5V output was at about 9V. This 
>wiped out the SC/MP, a couple of 2114s, and at least one TTL chip 
>(amazingly much of the TTL eurvived). 
>
>I was a schoolboy at the time, and it took a lot of weeks of saving 
>pocket money to replace that SC/MP. I guess that's why I'm now (over-) 
>cautious...
>
>-tony