Date   : Fri, 26 Jun 2009 18:05:20 +0100
From   : chris@... (Chris Long)
Subject: Only one beep

Mike Tomlinson wrote:
> In article <4A4347C0.7020209@...>, Chris Long
> <chris@...> writes
>
>   
>>    The current syptoms are that, on switching on, I get the first low 
>>    beep but not the second higher beep - does that indicate a specific 
>>    fault?  The caps lock LED coms on, and toggles as expected when I 
>>    press the CAPS LOCK key.
>>     
>
> OK.  It's _very_ nearly, but not quite, managed to boot.
>
>   
>>    I've checked the PSU outputs with a multimeter, getting +4.8 volts 
>>    on the +5 lines and -5.7ish volts on the -5 line - are these 
>>    voltages within limits?
>>     
>
> Yes.  4.8 is a little low; I'd have preferred to see it closer to 5.0.
> Is that at the power connectors on the board?  4.75 is the minimum.
>
> When I first saw your post I thought, ah hah, C9 in PSU.  If you leave
> the machine switched on for ten minutes or so to warm up, then hit
> Break, does it boot?
>
> Give all the socketed chips a shove to reseat them, and unplug then
> replug the keyboard cable at both ends to clean the contacts, and see if
> that helps.
>
>   
Hi Mike,

Thanks for your suggestions.  I figured it must be very close to booting 
- do you know at what point in the boot sequence the second higher beep 
occurs?  From what I've read, it seems that the video output chip is 
programmed during the boot sequence, and it doesn't seem to be getting 
that far, judging by the lack of any meaningful video display.  It 
didn't boot after letting it warm up, but I only tried that once so I'll 
try again.

Unfortunately I've already tried removing and replacing as many chips 
and cables as I could get to - there are some chips that I couldn't 
remove because other components block the path of my screwdriver, 
particularly the system 6522.  I'll have to improvise a chip removal tool.

Thanks for your time,

Chris.