24 Jan
2012
24 Jan
'12
6:08 p.m.
On 24/01/12 20:40, Tony Duell wrote:
I've seen HP service manuals that give signatures
for various testpoint.
They generally have a 'faultfinding' guide of the form 'If the
signatature at pin 3 of U6 is not 23H7 then change U1, U8, U12, U24 in
orde'.
I have a DIY spectrum analyser article that a friend photocopied for me.
Under "Aligning the IF1 filter", it reads:
First, obtain a calibrated spectrum analyser with matching calibrated
tracking generator.
Humm. So I need a spectrum analyser to make a spectrum analyser?
I figured you could use a homebrew swept-frequency generator, an ADI
logarithmic amplifier (in datasheet 'RF power meter' configuration), a
scope and a few junkbox parts to align it for about ?35...
In otehr words they don't tell you exactly waht
the fualt is and
ovber half the time you'd have guessed it was likely to be one of those
ICs (probably including the CPU, ROM and RAM) anyway
I'd test with the scope (because it's permanently set up on my bench
anyway) then dig in with a bus-sniffer and the logic analyser.
I prefer looking at symptoms and working back to probable cause. If I
can justify the time taken to set up the probes, I'll rig up the logic
analyser and sniff the CPU bus. The HP 16700's Inverse Assembler feature
really is the mutt's nuts.
Total overkill for most things though.
Some HP manauls are better htna others. In particular
many of the
computer nad desktop calculator manuals are pretty pointless. But since
I've figured out how to fix some of those without any official technical
info, I don't let the fact that they expect me to use a signature
analyser to mean I have to use one :-)
Now why does this statement make me think of the "SX Engine Schematic
Set, A.R. Duell Special Edition" as a prime example? :)
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/