I don't have a copy of the 7A26 schematic, so this is a *real* stab in the
dark. How long are the triggering events that you're looking for?
I fooled myself for a day recently while trying to fix my HP counter when I
was convinced that the input section wasn't working I was feeding it with a
1kHz square wave, and could see nothing at all on the bus lines coming from
the differetial line driver on that card. The reason? The output was a 5ns
duration ECL pulse at the trigger transitions of the input wave (as set up
by the trigger level controls). Once I triggered on the event, and then
sped the scope sweep up - there it was! Interestingly (and very tackily)
this is generated by using three ECL NORs in a loop, and the output pulse
duration is generated by the differential pulse delay of two gates - or
about 5ns for 10xxx series ECL.
Now since many of the y-amp 7000 series plug ins use custom silicon (as well
as the timebase), and much of this fast custom silicon is ECL-based, are you
sure that there isn't a triggering event there but of a non-intuitive time
duration?
Cheers
Craig
toggle quoted message
Show quoted text
-----Original Message-----
From: Lynn Lewis [mailto:mrzuzu@...]
Sent: 22 January 2002 09:52
To: TekScopes@yahoogroups. com
Subject: [TekScopes] Who's up to some remote troubleshooting?
I plan to get back to this after lunch today. Any suggestions would be
appreciated. It's not life or death, just my idea of fun.
Item: 7A26 with serial number B2....
Setup: This 7A26 is in a 7704 with a known good 7B53A. I am feeding both
channels, not necessarily at the same time, from the 1KHz square wave
calibrator. I started at .04V but have worked up to 4V. I'm using
a 7904 to
see the waveforms. The 7B53A is set to use the internal trigger.
Symptom: Can not sync through channel B using internal trigger. If both
channels are receiving square wave, it syncs. If channel A only
is receiving
square wave, it syncs. If channel B only is receiving square wave, it will
not sync.
Knowns:
1. I have another 7A26 that works perfectly in that same bay
so it's not the
scope and it's not the 7B53A.
2. If I feed the square wave only into channel B, I can use
the other scope
and follow it right up to U2750. The input pins to U2750 have the square
wave (fuzzy but square). The output pins do not (fuzzy and flat).
(Note: If
I feed the square wave only into channel A, I can see it on both the input
and output of U1750.) The DC voltages around U2750 are very close to those
indicated on the schematic and appear to me to be reasonable. I did
resistance checks on the resistors in the input network to U2750.
3. I have tried:
a. replacing U2750 twice
b. replacing U1750
c. replacing Q920, Q940, Q960, and Q980.
Suggestions:
To unsubscribe from this group, send an email to:
TekScopes-unsubscribe@...
Your use of Yahoo! Groups is subject to
