Scope maintenance

[Conrad Hoffman]

I don't remember specifics on the 453, but if it has a fan, clean the crud out and clean the filter. I use compressed air to blow off everything else, but not in the winter when the humidity is low and static potential is high. The auto stores often sell little 3/4" diameter "dashboard brushes", and I use those to get between tubes and such. Any controls getting stiff get some Breakfree or similar lube at the bushings. Noisy controls and switches get a shot of DeOxit. Everything gets a good visual inspection with a magnifier- look for cracked solder joints and wires on the verge of breaking. Look for toasted resistors and leaking caps. If the PS voltages aren't very close to factory specs, I check caps. I don't believe in replacing anything that isn't proven to be faulty- I want to see low value or high DF before pulling things apart because you can do a lot of hidden damage flexing old wiring and such. Those old Tek, HP, GR, EH, Kepco, Keithley and Fluke instruments performed brilliantly when new and it's important to know what's normal so you can get after problems when they're still minor.

Happy New Year!
Conrad

[tvrgeek]

Yea, really. We hobbiests can't afford meteorology services. It cost more than the used scope to start with. So, used 4 1/2 digit true RMS multimeter, used freq counter, used HP generator, and PC based tools for everything else. Then just dig out the o' Tek when I want to see the waveshape or relationship. No software scope can work anywhere as well as a real one for my pulser I use to measure speaker time alignment. Zalescope is close. Just wish they made one that could run 24 bit and 192K.

So, if you can set your probes to a nice square wave, be happy, don't worry. They were never that close to start with.

[Mooly]

Originally Posted by tvrgeek

So, used 4 1/2 digit true RMS multimeter, used freq counter,

Remember scopes measure and display peak to peak voltage and should be calibrated as such.

[AuroraB]

I don't know the prices outside Norway, but I'm responsible for a setup of appx 5-800.000 $ worth of instruments, all under ISO 9001 certification. The yearly checkup routine costs around 20.000$, - but then we do have some fairly expensive RF instruments.
The cal. checkup for an average scope is around 600$ a piece, - any repairs or adjustments will add up extra. All these checks are run by an accredited cal.lab. in our premises.
Thus if your old scope really needs a recal, I guess you are easily up for 1000$++ bill........
If you know someone who have access to calibrated instruments, I guess the easiest way is to pay someone for a quick checkup. Certified check and calibration is REALLY expensive.........

A good cleanup with a damp rag and some switch cleaning is usually almost free.....

[nigelwright7557]

Originally Posted by AuroraB

Thus if your old scope really needs a recal, I guess you are easily up for 1000$++ bill........

I only paid £60 for my scope so recalibrating it is not worth while !

[AuroraB]

A quick check of the input amps can be done using DC, and a regular multimeter. It will at least tell you if it's way off. Comparing freq. against a counter is another quick check. Waveforms are more tricky, as you really need a good generator, and most cheap ones are not, IME......


BTW - last year we decided to remove all the cheaper hand multimeters from the cal list....what's the use of paying 250$ to check a 200$ meter...
instead we set up an internal check service against certified instruments...

[Mooly]

I remember having an "argument" with the company I worked for... we were the "consumer electronics" side of a major power company, and they saw fit to insist our DVM's were calibrated, and that the "calibration" was to be performed by themselves .
I asked what standards they were using... and was amazed to hear something along the lines of... well it has to read 240volts to within 10%... absolutely unbelievable.

[AuroraB]

240V +/- 10% used to be the spec for mains power , not an instrument!
Someone clearly had misunderstood grossly....

[Mooly]

It got worse... they then "insisted" that our workshop was "unsafe" as it was earth free (all on isolation transformers)... earth leads snipped off in plug tops etc.

A little demo with earthed scope and leads and soldering iron and live TV chassis soon showed them the error of their ways... they left us alone after that