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 Caution with aging Multimeters
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 Return to top of page · Post #: 1 · Written at 10:28:45 PM on 17 December 2013.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 2747

A note to all those using older Multimeters; Many of us keep these meters as the analogue meter, is not obsolete.

Due to the way that Digital meters sample, then display (Sample rate) this can cause them to have serious accuracy issues in some applications. So for dirty DC (eg Brush motors & automotive generators) and with some to avoid the issues some digital meters have with RF: We keep an analogue meter.

Of concern now are the capacitors within them and several other bits of test gear. I sometime ago had the 400VDC range of an AVO 7x give a bizarre reading. This was rapidly, after looking at the circuit, traced to a failed cap.

Recently I had cause to look at a veteran Peak 200H from a collection to see that it did not have a leaking battery in it. I noted that it had an oil filled type cap in it. I have seen them explode and consider them no better than the wax papers one replaces on sight. This cap was leaking as expected.

I also had a VCT valve & circuit tester in to fix a cable issue. It had paper caps, it has no longer, they failed leakage test badly.

There is no place for leaking, or out of tolerance caps in a test instrument. Do keep an eye on this.

Marc


 
 Return to top of page · Post #: 2 · Written at 7:34:38 PM on 18 December 2013.
Redxm's avatar
 Location: Tamworth, NSW
 Member since 6 April 2012
 Member #: 1126
 Postcount: 401

Good advice Marc, as usual.

Im at the stage now, where the collection is tidy, I'm checking all my test gear. I did a few quick repairs 10 or so years ago, but this time they get a hamburger with the works.

If you cant trust your instruments you may as well chuck them away.


Ben


 
 Return to top of page · Post #: 3 · Written at 3:17:20 PM on 19 December 2013.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 2747

I have a Heathkit OS-1 that had to be gutted decades ago, this appears to need the electrolytics doing again.

The BWD-539C also needs a pot replacing. I have not absolutely studied the mechanics, however the extended drive shaft is connected by a wire not dissimilar to a paper staple. That means the new pot has an appointment with a drill press.

It also amazes me that on several forums, time & again there are people trying to align radios with signal generators the accuracy of which is an unknown. And they have no idea on how to sort that out.

Marc


 
 Return to top of page · Post #: 4 · Written at 4:39:19 PM on 19 December 2013.
Art's avatar
 Art
 Location: Ipswich, QLD
 Member since 22 October 2013
 Member #: 1437
 Postcount: 886

BWD 539C is the same as mine Smile
I have given it thought, replacing at least electrolytics.
It makes sense, it's almost as old as me.


 
 Return to top of page · Post #: 5 · Written at 8:07:49 PM on 19 December 2013.
Redxm's avatar
 Location: Tamworth, NSW
 Member since 6 April 2012
 Member #: 1126
 Postcount: 401

It also amazes me that on several forums, time & again there are people trying to align radios with signal generators the accuracy of which is an unknown. And they have no idea on how to sort that out.

Yep. I calibrated my old Palec years ago. To say its a tad out would be an understatement.

Thankfully I have access to modern calibrated gear to reference against. Still, knowing what I have is accurate is a big plus.


 
 Return to top of page · Post #: 6 · Written at 9:25:06 PM on 19 December 2013.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 2747

BWD has fairly modern caps, unless I see signs and whilst it is working, I am holding back on it. I scored it for $30 with both original probes & paperwork. Took about 2hours to pull things to bits & clean it. Filth is what ruined it's sale price: my gain.

My sig gens are old and basic. I use frequency counters to set them. The counter has its own calibrator, but even so I do zero beat it against the comms receiver (digital) & WWV &WWVH. to ensure that they are as they should be.

If you sync the CRO to the audio of the sig gen waveform is more stable.

Beware with the counters, most of them will not calibrate accurately if the signal is modulated.

Marc


 
 Return to top of page · Post #: 7 · Written at 9:02:37 AM on 20 December 2013.
Wa2ise's avatar
 Location: Oradell, US
 Member since 2 April 2010
 Member #: 643
 Postcount: 620

QUOTE: It also amazes me that on several forums, time & again there are people trying to align radios with signal generators the accuracy of which is an unknown.


One could check the calibrations by checking to see if you can "jam" a radio station with a known frequency, and see if the calibration marking on the generator is close. Though be aware you could be on an image frequency, usually 910KHz higher, for radios using 455KHz IFs.

You can also check the generator for accurate IF freqs by trying to jam the IF frequency of a known good modern radio, one using those little ceramic bandpass filters. Though these come in a variety of frequencies, like 450, 455 or 460KHz. You have to look to see which the radio has in it.


 
 Return to top of page · Post #: 8 · Written at 9:49:53 AM on 22 December 2013.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 2747

A lot of the older generation of sig gens had provision for a crystal, which you could (After acquiring) zero beat with the machines own oscillator.

The major issue of course, that favours using, or putting one on it, a counter; is that there is quite a wide range of IF frequencies and the counter has a more precise readout.

Marc


 
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