Bob et all
1) We have a 1st class scan of the R-D 4200, manual with complete
schematics available at a modest price
2) We have a VERY NICE scan (NOT a retread of the poor quality of
Agilent scan) 600dpi scans of the schematics full size up to 27"x 11"
unpieced, again at a very modest price
3) I am sorry but we dont have manuals for the EI or Valhalla unit at
the moment but I have added them to my "watch for these list"
I have been following your saga on the 3456A repair on the Agilent forum
and don't have much to add except to say this is not a trivial unit to
troubleshoot because of the overly (IMO) complex nature of the beast .
To paraphrase the old nursery rhyme, "When they are good they are very
very good but when they are bad they are horrid". I'd probably put that
one on the back burner till you get more time , patience and experience.
Then sit down and a read the theory of operation section of the manual
till you can recite the whole thing by heart..THEN go digging into
boards. With a unit this complex there are scores of feedback and
reference check loops that it is often difficult to ascertain when
troubleshooting what is a " root cause" and what is an "effect" of some
other defect elsewhere in the circuit
ON the erratic Racal unit, by comparison this is an easier unit to
repair with a fairly clean layout of the main board. I would start by
carefully unplugging and reseating all cable connectors and the Data I/O
board, Display board and power supply diode board. next once the unit
begins its erratic behavior after warm up, look at ( with a scope ) the
AC ripple on the DC +5V and +20V supply buses . Most likely suspects
with any unit more than 25 years old ( aren't they all?) are the
Electrolytic and Tantalum capacitors followed by solder joints that just
need to be re-flowed. Given the lower complexity of the Dana main board
the joints could all be re-flowed in 1/2 hour, One other common source
of noise are the calibration pots...which need to be turned back and
forth a few times to clean the wipers.. of course after this brilliant
move you will need to do a complete recalibration of the unit.
Good luck
Dave
ArtekManuals
OnceOn 2/23/2014 1:07 AM, Bob Albert wrote:
Pete,
The EI is in three parts connected by many massive cables. When I say it's
pretty close, I mean it agrees with everything else I feel is close. The 3456A
has a -12V reference which the EI measures at -12.0026 or so. It uses an oven
so it takes a half hour to settle. I have pics of the panel and would post
them if I knew how.
The Valhalla is actually a good meter but one range has a small problem. The
Racal-Dana is unfixable because I can't find a manual, short of spending more
than the meter is worth. Those two units are very similar; the main difference
is 1) the Valhalla measures AC current and 2) the Dana has a very sensitive DC
microammeter such that I can measure diode leakage.
I am befuddled by the HP3456A. I have replaced some parts but so far it's not
doing its thing. I have the manual but it sucks, not having a proper schematic
diagram nor a board trace layout.
The Calib Stds unit is nice, a manually operated slideback DC volts only unit,
compact and easy to use. Again, no manual available and, in fact, no mention
of the company anywhere online. They were in Los Angeles area.
The main reason I want to fix these is that I hate owning anything that doesn't
work. And I like knowing my meters are accurate as well as precise.
I also have some 10V reference ICs that have been around here a few years.
They all agree within a few mV. I made a permanent reference out of them with
a switch to select each, and they are running whenever I am in the lab.
Bob
<TRIM>
--
Dave
[email protected]
www.ArtekManuals.com
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