9 Feb
2007
9 Feb
'07
10:26 a.m.
Hi Warren,
Yeah, wunnerful... I suppose it's great for current products if you have the HP
service tools, and you can still get board replacements. Not a cheap way to repair,
but perhaps when a customer pays $10,000 for a scope, he doesn't mind paying for
whole boards (I'd guess they wern't all that cheap). Be nice to have some real
service information for the times when board level repair is needed however ...
Thanks for the info.
I checked the supplied, they look pretty good and are within tolerance
for DC voltages, I couldn't find a spec in the service manual for the
ripple - Here's what I measured, some of them are beyond a single
digit mV reading.
Supply Spec.(V) Measured(V) Ripple(mV)
------------------------------------------------
15 14.25 15.75 15.12 15.8
12 11.4 12.6 12.19 5.7
5 4.75 5.25 4.99 2.8
-2.4 -2.16 -2.64 -2.52 4.9
-5.2 -5.2 -5.7 -5.41 13.0
-12 -11.4 -12.6 -12.02 3.7
While I was measuring the power, the scope started
to work correctly again - probably only after about
5-10 mins of power-on, where yesterday I let it sit
for several hours...
The readings did not change significantly from when
it was not working to when it was working. Voltage
and ripple were about the same in both cases.
When it's not working, it triggers constantly on all
sources - setting the trigger range all the way to the
top doesn't stop it from triggering, however setting
it to large negative values will usually stop triggering.
At this point, applying a signal can make it trigger,
however the trigger points appear to have no correlation
to the input signal.
When it starts working, it's not a gradual shift - it
just "suddenly" starts responding to normal trigger
levels. It doesn't seem to me like a symptom of a slight
change in power supply ripple...
I'm thinking that something in oscillating that shouldn't
be ... with no input source the trigger should be at a
constant level, presenting no edges - the fact that I
can set the range over such a large area suggests that
there is a fairly big waveform "somewhere" along the way.
Problem is the analog board is a big board with several
large chips that I don't have any information on - I can see
that the external trigger goes to it's own and somewhat
simpler area of the board, so I will probably begin by trying
to follow that through, but I imagine I will have quite a
ways to go since the problem is deep enough in that it affects
all trigger sources (except the digital analyzer trigger - that
seems to always work, but I'd guess it doesn't come into the
mix until some time after all the analog stuff has turned
digital)... having some information on signal paths would be
very useful ... anything you can provide would be MOST
appreciated.
Regards, and thanks again.
Dave
--
dave06a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools: www.dunfield.com
com Collector of vintage computing equipment:
http://www.classiccmp.org/dunfield/index.html
I used to repair them, from time to time.
Thanks for responding - thats good news. Do you have any more
detailed technical information than the ...
I've
obtained the HP "service manual" for this scope, and it is absolutely useless,
no schematics, not technical descriptions... Basically, it says "Plug the scope
into your HP scope tester, press GO and replace any boards which are listed
as FAILED".
That's the "HP Way" to repair. This morning,
it's been on for over three hours and it's still triggering
continously, even with no signal inputs (leads disconnected). Triggering
calibrations fail consistantly for both channels. So I think it has finally
gone bye-bye.
When it works, this scope is awesome - I would really like to get it
working again - any information/help would be greatly apprecaited.
A quickie: Check the power supplies for ripple. I don't remember
the tolerances, but they ARE small, somewhere in the single digit mV
range. Ripple on the power supply gets into the triggering circuits,
and is taken as input, firing off the trace. It's worth a shot -- it's
REALLY easy to check. AC voltmeter to the supply...