The pics are in imgur under voltnuts.
Bob
On Sunday, February 23, 2014 1:47 PM, Bob Albert <[email protected]> wrote:
Pete,
Oh yes those Harbor Freight jobs have to be the bargain of the century. And
from time to time they even give them away.
I am currently checking my time base calibration against WWV at 20 MHz. It's a
treat when I can hear them at that frequency so I try to get as close as I can.
I usually can get within 0.1 Hz for an error of only 5 ppb, not too shabby.
Harder to calibrate voltage though. My IC 10V standards are presumed to be
within about .05%, close enough for most work but I want to do better. I do
have five of them and can average them but that's subject to systematic errors,
since they are all from the same vendor (I think). And that doesn't count
aging, important because they are at least 10-15 years old.
Bob
On Sunday, February 23, 2014 1:17 PM, Pete Lancashire <[email protected]>
wrote:
Again just my few cents
1 KV on the classics
Be very very careful. I was not uncommon for both of these guys to arc over. If
you do work with voltages in that space, consider a divider probe.
If you do keep playing over about 4 digits at some point you going to need to
decided that your absolute measurements are not important or get something
like the 3456A calibrated, or the calibrator you have. I've had good luck with
one of the
few meteorology labs where I live having things calibrated for very little as
long as I don't want that little sticker.
Once they found out I had a just acquired set of L&N 4000s that I wanted to
cal, they even let me do it myself.
For a few $'s there is a small one man company in Washington state that sells a
nicely done set of voltage sources. http://www.voltagestandard.com/ If you add
up the parts cost, etc. they are a bargain and well built (not a customer but
would be if didn't have the stuff I have).
-pete
There is a H-F about 1 mile from where I live. One day there were about 20 of
the Red DMM in the dumpster, I could not resist. Fixed all except 2 put 2 in
the truck and gave the rest away. 90% assembly issues.
On Sun, Feb 23, 2014 at 10:21 AM, Bob Albert <[email protected]> wrote:
Well all comments are appreciated and well noted. The 3456A is indeed a
Pandora's box and is, as suggested, on the back burner for now.
As for the Dana, I have tried all the above. I replaced one IC that seemed to
be the root of the trouble, to no avail. The unit is very clean. I spray
cooled it when it did its trouble thing and it came back to operation but I
haven't been able to find the offending component or solder joint. Power
supply seems good throughout.
I paid so little for this, and I have so many other units, that I am loath to
spend money on a diagram, especially when it is no guarantee of giving me the
needed information. Plus, the 300-page HP manual is free for download, so it
feels like the tail is wagging the dog here.
I will pay attention to the KO4BB site for when the HP manual will appear.
But if I need to measure something, I certainly have the tools to do it. If
the voltage is above 1 kV I have my Simpson 260 and Triplett 630-NA for that.
And I am ashamed to admit, a couple Radio Schlock VOMs. The whole thing here
is that I enjoy playing with accurate stuff even though I have no legitimate
use for 6-digit voltage measurements.
One thing about the HP that appeals is the accurate Ohmmeter. I have a GR 1658
bridge that is very accurate but it doesn't measure at DC, so is cumbersome for
inductors, etc.
And of course the delightful little toy, the Harbor Freight DVM, is a bargain
that can't be approached by 'normal' units. I have several of them and, within
their limitations, they are great units. There is a calibrate pot inside that
takes care of any ordinary reading errors. And if I blow it up, I pick up
another without that dreaded feeling of having broken something valuable.
Bob
On Sunday, February 23, 2014 3:55 AM, Artek Manuals <[email protected]>
wrote:
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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