25 Aug
2014
25 Aug
'14
1:01 p.m.
On Mon, Aug 25, 2014 at 12:14 AM, drlegendre . <drlegendre at gmail.com> wrote:
I don't use a 'scope all that much, actually.
Obivously the insturment I use most is a multimeter, since checking PSU
voltages and finding broken conenctions is a common task. But after that,
I wopuld use a logic analuyser much more than a 'scope. I find the
ability ot be able to see 16 signals at a time (albiet as only 0's and
1's to be a lot e more use than seeing 2 or 4 signals as votlage waveforms.
It does depend on what you are doing, though,and there are times wien I
need a 'scope (jsut as there are times when oyu _ened_ a logic analyser
[1]).
[1] Depugging microdeed CPUs is one such, things like the HP9800 family.
Being able to feed the 8 bit microcode address into an LA and thus trace
the microcode really speeds up debugging.
If you can find one, the HP LogicDart is a very hand yhadnhedl thing. A
combined voltmeter, continuity tester, frequency meter and 3 channel LA.
It does not replace a larger logic analyser with more channels. but ti is
small enoguh to throw in the toolbox and take to the job.
I just realized something, about the flashing
LEDs..
They're not just flashing, I think the thing is +running+ or at least
counting. It's counting up through the entire 16-bit address space, and
If you're going to do much hardware work, I'd strongly recommend getting
an oscilliscope. You want at least three times the bandwidth of the highest frequency digital signal you are going to look at, so
for old 8-bitters, I'd
recommend having at least 30 MHz bandwidth, but you can probably find
a used 100 MHz analog scope (e.g., Tek 465) pretty inexpensively. You
don't need the scope to be well-calibrated, but it does need to work, since
you don't want the scope to also be a repair project, especially for something
as complicated as a Tek 465. I paid about $100 for a working Tek 465 last year.
Oh I don't know. Fixing old Tek 'scopes is fun. For sutiable values of fun...
If you want test equipment suitable to work on modern
computers (anything from
the mid-1990s and later), you're talking Really Big Bucks (tm). IMNSHO,
One reason why I will not depend on such machiens if IO ahve ot maintain
them...
it's not even worth wasting time trying to do any
hardware repair on newer
stuff, since they aren't designed to be serviced. The manufacturer intends
And even if you ahve ythetest gear and can fidn the faulty compoent,
99.9% of the time you can't get it other than as part of the FRU.
For classic machines it can be useful to be able ot find fault ASICs even
if tehy were never avaialbel as spares, since it may well mean you can
get oen workign board otu of 2 fautly ones. But for modern stuff it's not
really worth it -- yet.
I find the service manual for my digital TV set very amusing. There re 2
PCBs in there. A PSU (sonventioanl SMPSU) and the signal processing board
complete with BGA packaged ICs, etc. The service manaul regards the PSU as
a single FRU, no schematics, but you are expexcted to repair the signal
proccessing panel to component level armed only with the schematic. Go
figure...
-tony