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Old 21st Mar 2015, 9:58 pm   #7
Radio Wrangler
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Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Default Re: Levell TM14 Modern Equivalent?

Thanks, Bill, that circuit's quite interesting.

10 Tera-Ohms, eh? but no guarding tracks and all that jazz? I wonder what their PCB material and process is?

It looks like a reasonable insulation tester, but it doesn't seem to have what it would take to live up to some of the headline figures.

The most exotic part in it seems to be an LF35? opamp, probably an LF356? Transstors 11 and 12 doing the log conversion might be fancy but maybe not, they haven't gone for supermatched pairs.

As long as the meter movement is OK and no switches have been mangled, it ought to be fixable.

For one with no voltage output, then as sid above, the multivibrator and transformer are the places to start.

David
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