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Peavey 701R mixer query

or perhaps Fluke 77 DVM problem.

Have removed all the rear securing bits, so partly veiw interior, and before removing all the front panel knobs etc, probably on Wednesday. One of the first things I do , as a matter of course, is measure the mains primary DC resistance and note it down.

On autoranging of the DVM, cannot do so, as unstable display as though there was a voltage on it. No DC or AC V on the primary which would , if absentmindedly, place it in ohms setting on an active circuit. Can measure 237R if I set the Fluke on fixed range. And also measures 237R on another meter. Thinking it is a "bug" with the autoranging if it hits about 237R, I added 1K in parall with the Fluke 77 in autoranging mode and it still is unreadable.

What would be inside this Peavey with the what looks like conventional linear mains transformer that would give this DVM problem?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N Cook
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Due to very unusual high inductance of 25 H , set as 240V, could measure the DC resistance on Fluke if split over each 120V primary.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N Cook

============== Measuring large inductances with an autoranging ohmmeter can be disconcerting. The reason you're experiencing that phenonenon is because of the range-determining circuitry in the meter. Each ohms range injects a specific current into the test leads, measures the voltage developed by that current, and then displays the result as a resistance. When the meter switches range, the current undergoes a step change. The inductance of the xfmr winding causes an abrupt voltage change, and the meter sees that as an overrange or underrange condition, and switches range. This causes another step change in the current. The meter senses overrange or underrange condition. The range switches again... ad infinitum.

Best way to measure the resistance of large inductances is with an analog ohmmeter or a manual ranging DMM.

Dave M

Never take a laxative and a sleeping pill at the same time!!

Reply to
Dave M

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