Date   : Wed, 24 Feb 2016 23:34:14 +0000
From   : pete@... (Pete Turnbull)
Subject: Acorn PET and FIT boards

On 24/02/2016 22:59, John wrote:

> I?ve never seen these, so forgive a potentially silly question ? Acorn
> PET and FIT testing boards ? worth having, and if so has anyone tried to
> replicate their function using modern components?
>
> Are they any kind of substitute for, say, an Oscilloscope or similar
> test equipment? Or are they just giving yes/no answers to inform quality
> control?

The FIT - Final Inspection Tester - is basically just for quality 
control.  With the FITest program (on tape, disk or RFS from another 
Beeb) it checks most of the functionality of a Beeb (A or B) but it's 
not really a diagnostic aid, it just tells you if everything works (or 
not).  It won't work at all unless most of the machine is working.  When 
I ran an Acorn Approved Service Centre we found a small number of times 
it passed a machine that wasn't absolutely OK, but not many.  I still 
have mine and use it occasionally.  It's a circuit board about 10cm x 
26cm with connectors/cables for most of the I/O ports.

The PET - Progressive Establishment Tester - is a more complex animal on 
a circuit board about twice the size of a FIT.  It too has lots of 
connectors, including a clip that fits over the 6502, and some other 
internal s well as external connections.  The theory is that it runs 
on-board diagnostics, testing the CPU, then memory, then various 
functional areas, not relying any part of the machine until that part 
has been tested.  It has a couple of 7-segment displays for the 
test/fault codes.  It's quite useful, but we found a scope and logic 
probe often quicker, and we also had some simple diagnostics in EPROM on 
a carrier with a BCD switch to select the test(s) we wanted - many from 
examples in one of the service manuals plus some I wrote - which we 
substituted for the MOS.  I didn't keep our PET; I think one of my staff 
got it.

-- 
Pete