powering up older machines - is it safe?

[Jules Richardson]

Antonio Carlini wrote:
> Tony Duell wrote:
>>                                             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.
> 
> I can understand worrying about something that's not been used for
> a few years, but if you check everything that's not been used for
> just a few months, when do you have time to actually _do_ anything?

I suspect most peoples' collections fall into two categories - the stuff that 
gets used much more frequently than every few months, and the stuff that 
hardly ever gets powered up at all. The former's less likely to need checking, 
whilst if a system gets powered up very infrequently it's not much bother to 
give it a proper checking first.

> The only thing I remember going phut round here is a Rainbow
> a few years ago - and that failed while trying to format a disk
> (so it had been running happily for a morning or so while
> I was playing with it).

I've had all sorts go bang. The last system I worked on had a PSU fault where 
the +12V rail would no longer supply rated current - at startup the supply 
would invariably go into a loop where it'd detect a fault and shut down, only 
to try coming back up again moments later. I never did 'scope the +5V rail, 
but it wouldn't surprise me if there was all sorts of potentially-damaging 
noise on it under those cycling conditions.

> When I get around to trying out the 380Z I'll most certainly
> not plug it in and hope (have you seen the size of the cap in
> that beast?)

I've seen two types in 380Z's - some have much smaller caps, but like you say 
some of their PSUs used ones that were huge.

I still need to debug my system properly sometime - it blows fuses when the 
little RGB analogue board is plugged in (I used to use it with composite 
output all the time, so I never quite got the necessary tuits together to fix it)

cheers

Jules