24 Jan
2012
24 Jan
'12
2:25 p.m.
On 01/24/2012 03:43 PM, Tony Duell wrote:
I agree 100%. Last night I repaired an HP 5340A frequency counter
and a Tek 7834 oscilloscope frame. (both glorious instruments) I had to
trace through a fair amount of circuitry in both cases, and I learned a
lot about both designs.
In the "credit where credit is due" department, I had a kind assist
on the 5340A from Dan Roganti who was here at the time. He kept telling
me to look at the Range switch, and I kept saying it couldn't possibly
be that switch contact making partial connection when it shouldn't have
been...eventually I looked at it to shut him up, and sure enough, that
was it! ;) It was holding the counter in reset. I now know how the
control logic of the 5340A works.
The 7834 frame had a 1M HV resistor on the focus power supply board
that had failed open, putting a solid and uncontrollable 400V on the
focusing grid. I now know how the focus power supply of the 7834
works...and what an amazing design the rest of it is. Holy cow, have
you seen that scope?!
In the case of the 3456A, though, it's an instrument from a working
lab run by a friend of mine, and he lacks the budget to have it
repaired, and I just want to get it working as quickly as possible to
help my friend, by any method necessary. The alternative would be to
loan him my beloved 3458A, but that beautiful instrument isn't leaving
my sight! ;)
-Dave
--
Dave McGuire
New Kensington, PA
The advantage
of the signature analyzer (SA) was you can deal with
circuits that have feedback loops more easilyand without the need to
fully understand the operation of the circuit. For example servicing
And that is precisely why I don't like it. I feel you can only reapri
something -- and know you've repaired it -- if you understnaf how it
should work, know what it's acutally doing, and then figutre out what
could cause the behaviour you're obseerving.
Signature analysis doesn't seem to help with this.