Improving older test equipment

[1audio]

I have plenty of good stuff to give away to some enterprising types. I need space in my storage and its not getting used. You must come to me to get it, however.

[Wavebourn]

Originally posted by 1audio
I have plenty of good stuff to give away to some enterprising types. I need space in my storage and its not getting used. You must come to me to get it, however.

Did you get my e-mail Demian?

[SyncTronX]

Originally posted by anatech
(snippage)
To properly clean the switches in any test equipment involves care and attention. You must carefully apply the cleaning solution to a wood shaft "Q-Tip" (or similar) and very carefully rub the center contact rings. They will become shiny as you clean them. You will probably have to remove some of the cotton first. Take extreme care you don't get the cotton caught in a contact "finger" in case you bent it (Baaaad news!). You will get the hang of this. Once clean, rotate the control knob to get the cleaner on the inside of the finger contacts. Follow this up with a zero residue cleaner, plastic safe. Hold the instrument up-side-down so that nothing drips onto the interior. Do not get anything in a trimmer capacitor - ever!!!

Your Fluke 87 meters are very good and do tend to hold their calibration ... except you can not depend on the higher frequency AC readings at all. An HP 339A is more accurate on AC than a Fluke 87. Why you ask? Simple. The person who calibrates a Fluke 87 knows that once you change the case, or reinstall it, the AC readings take a wander. The most accurate way to align an 87 is to use another top cover with access points drilled out. Do the adjustments and reinstall the proper case. Then check to see how far out they are. I kid you not. If a replacement cover was not used, consider the higher frequency readings as if they are vague suggestions unless you have before and after readings in you hands that prove the readings are correct. I can say with certainty that one that is right on is a rare piece. Later Fluke meters that use what is called "closed case calibration" would be expected to be in tolerance.

Have I caught everything you were wondering about?

-Chris

Interesting. Glad to know I've got some good meters just
no good scope or distortion measuring equipment.

I've got the Fluke 87 true RMS Multimeter, a recent find
that didn't work when I purchased it (pawn shop).

How ever it had been calibrated, dead battery and blown
fuse. Had to break the seal to replace the fuse and battery
only to find the LCD didn't work. Arrg!

I was really surprised that all was needed was a cleaning
including the LCD contacts and etc with a little bit of D5
and some pro gold and most of the mater is still working.

Next up is trying to fix the speaker/continuity circuit in it.

My Fluke 85 Series III is doing just fine.

My first meter, My Fluke 21 series II is going south on me
with display and other problems. I'll give her a cleaning and
see how she does after that.

Haven't opened up the B&W scope yet, but thinking maybe a
good cleaning is all she needs too.

So how high a frequency are we talking about with the
Fluke 87?

How would that compare to the Fluke 85 III?

Thanks,

Sync

[jackinnj]

Originally posted by janneman
I have a question to you test equipment buffs:

I was offered an HP 3721A Correlator:

http://www.helmut-singer.de/pdf/hp3720a-3721a.pdf

What's that good for??

Jan Didden

I was in my wife's laboratory day -- and there were a pair 0f "Correlators" in there -- used with the rats (as expected).

It's in the part of the lab in which the critters attain their useful end.

[slbender]

BSGD -

I seem to recall several "updates" to the HP339A and one I think..... was to make it more stable wrt those "overload" lamps (I don't think they used leds in 1977).

There is also a possible factory goof - a missing jumper in some 339A instruments that should be checked for.

I'm busy for the next few days, but will try and grab my 339A and duplicate your four simple tests and see what readings I get on one or both of my 339A's.

Did you just connect Gen Output to Analyzer Input with no resistors across or what?


-Steven

Here' are some interesting observations:

1- Internal oscillator directly connected to the analyzer input. INPUT RANGE set to .1V and OSCILLATOR LEVEL set to .1V (1kHz freq). ALL filters OFF. Measured distortion is .0215%.

2- Internal oscillator directly connected to the analyzer input. INPUT RANGE set to .1V and OSCILLATOR LEVEL set to .1V (1kHz freq). LP 30kHz filter ON. Measured distortion is .0044%.

3- Analyzer input shorted. INPUT RANGE set to .1V and frequency set to 1kHz. All filters off. Measured distortion is .006%.

4- Analyzer input shorted. INPUT RANGE set to .1V and frequency set to 1kHz. LP 30 kHz filter ON. Measured distortion is .0015%.


There is also something 'weird' going on: When the oscillator level is set to 30mV or below (and its directly connected to the analyzer input), the LEDs that indicate where to turn the INPUT RANGE control to select the correct one seems to misbehave. The LED indicating I should turn the range to a lower value stays lit all the time (it only goes out when I reach the lowest scale: .1mV).

At 100mV or more it behaves diferently: When I reach the proper scale, both LEDs go off, but if I keep down-scaling they dont light up. For example: If I have a 100mV signal being fed to the analyzer, and INPUT RANGE is set to 3V, the LED indicating I should lower the scale lights up. When I reach the 100mV scale it goes out, but if I keep turning the scale down to 30mV or less, both LEDs stay off and dont inidicate I should turn to a higher scale.

[anatech]

Hi Anatoliy,

I love mine HP 400D

I did too. It stayed with the shop I sold. I doubt those guys see it as anything but an obsolete old meter. They wanted to keep it only because I wanted to take it. I'll bet it's sold or trashed by now. What a waste!

There are times when some of that "old gear" is very relevant today. If I see another one, I'll be sure to pick it up. The only ones I have seen were selling for extreme $$ because it said HP on the front panel.

Hi bsgd,

Unfortunately I cant test with another oscillator, as the only one I have is the one built into the HP.

I am requesting that you use external cables. I did intend that you use the instrument you have there.

Please, read my suggestions again and retest. Let us know what you get.

-Chris

[SyncTronX]

Fluke Updates:

Fluke 21

Now functioning and operating fine.


Fluke 87 True RMS Meter.

Had to pull it back apart,
re-cleaned everything, and inspected the speaker.

When inspecting it I noticed the tiny black rubber
standoff on the face of the speaker was damaged.
So, it took a bit a patience, of pulling it, turning that
standoff around because part of it turned into a point
rather then a cylinder. Then I had to superglue it to
keep from falling out.

I also had to add a few pieces of felt because on leg of
the hold down for the plastic back cover was broken and
for the speaker to work properly it need full contact with
the circuit board.


Fluke 85 III

The ohm, capacitor, diode meters took a hit.
These blink after a brief check, etc.

Have to figure that one out.

Sync

[jackinnj]

here's something in the process of being "improved" -- it's the front end of a Radiometer pH meter -- I offered this thing for nothing on EBay and on the ham newsgroups -- no takers -- so it got a radiometer-ectomy -- inside is a very nice low noise amplifier, huge meter, +/- 15VDC power supply.

[anatech]

Hi Jack,
That's a really nice, clean job there. I am impressed.

-Chris

[wrinkle]

Yet another try to get past the posting woes of the last two weeks...

I have a bunch of dranetz 305C's, great for measuring phase to 700KHz, a 7150, a racal dana 5004, good for low ohms, and some other stuff, 7904, 141T and plugins etc, gets most of what I need.