Date   : Sun, 30 Oct 2005 18:09:25 -0000
From   : "David Harper" <dl.harper@...>
Subject: Re: Flying Blind

> Just had a weird afternoon !  I decided to try a BBC B I had bought ages
> ago (from 8BS) for the first time.  We have an "old" tv that the kids use 
> but is perfect for tuning in the Beeb - until the kids decided to move it 
> and dropped the thing !  (The tv, not the Beeb !).  So - no usable tv for 
> now until I can get my CUB monitor from its storage place in the loft. 
> Our "modern" tv is hopeless at tuning in and you need a science degree to 
> figure it out :-(
>
> Anyway, I plugged the Beeb in and turned it on to make sure at least it 
> did what it should.  But all it did was give a constant beep.  Not good ! 
> So I investigated further.  It has an additional ROM board installed and I 
> noticed the pins were not seated all the way home in the sockets on the 
> main board.  I removed the keyboard, removed the ROM board and re-seated 
> it.  Then put the keyboard back and made sure all the connections were 
> sound.  I then switched it on again and got the familiar 2 tone beep.
>
> Now to the question - Is it likely that the machine could have been 
> damaged by the extra ROM board not being fully seated when I first 
> switched it on ?
> Now that I get the 2 tone beep, is this a good indicator that all is well 
> ?

The first part of the two-tone beep is just a result of the way the sound 
chip powers up. The second part is a deliberate beep issued by the MOS 
towards the end of the reset sequence on a hard Break (i.e. Power-up or 
Ctrl/Break).

In other words, the two-tone sound means that at least most of the reset 
sequence has completed successfully. Various things have been done using the 
RAM by this stage, and several Sideways memory calls issued. This suggests 
that the CPU, the MOS ROM, most of the Sideways ROMs and at least part of 
the RAM are (probably) OK. (It also means that the sound chip and speaker 
works!) It doesn't prove that all of the interfaces will operate correctly, 
but it does mean that the "heart" of the machine is probably fine.

David Harper