Date   : Mon, 22 Jan 2007 06:30:57 -0600
From   : julesrichardsonuk@... (Jules Richardson)
Subject: Narrow Escape...

Ian Wolstenholme wrote:
> Yes, only 3 weeks in and already we have the
> first BeebMaster explosion/fire/disaster of the
> year!

Congratulations :-)

> Unfortunately I had accidentally connected the
> 5V on the host adapter up to a 12V supply, with
> "hilarious" consequences.

Youch. TTL chips generally don't like +12V...

How much damage probably depends on what order things broke in.

Worst case you're probably looking at:

   Blown chips on the SCSI board
   Blown bus buffers on the BBC [1]
   Dead +12V line on the BBC PSU [2]

[1] I think the 1MHz bus is largely buffered (unlike the TUBE) and so an 
over-voltage on any inputs would just take out the buffer ICs. (I'm assuming 
that the Akhter board plugs into 1MHz bus, not TUBE)

[2] I don't think +12V gets used for anything other than the aux power socket.

> Is it just the case of replacing the capacitor on the
> host adapter or could I have blown some of the chips
> as well?

You've almost certainly got one or more dead chips on the host adapter :( 
There's probably not *that* many on there, so it'd probably be quicker to 
replace them all than trying to diagnose which ones have failed.

Test the beeb out too and see if the 1MHz bus is still alive - and check that 
+12V still works...

> Just think what might have happened if I had had
> the LV-ROM connected to the host adapter at the
> time.....

True. Having just looked at a photo of the SCSI board, it looks like the 
player uses a NCR SCSI controller chip; there doesn't appear to be much in the 
way of buffering between that and the SCSI port, and depending on the type of 
chip it may be hard to find a replacement...


cheers

Jules