Fluke 79 acting up

Sorry, it's a 77, not a 79.

did you check the fuse in it?

on

with

as

I invested in a moulded rubber surround for my 77, after repairing one that had been jarred and the main SMD chip had loosened. Someone I know managed to put his knee on his, while working on the floor, and also dislodge the main chip. Both repaired after attending to the main chip.

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

This might seem stupid, but have you checked the battery? Is the "lo bat" annunciator displayed?

I have the rubber surround, and it hasn't been jarred, it was sitting in the closet where I always keep it.

I ordered a Fluke 187, I've wanted true RMS for a while anyway. When that gets here I'll use it to try to fix the 77 and use that as a backup.

It's not displayed, but then I suppose it's worth checking the battery anyway, I haven't, will do that tonight.

You should check its battery, that's where your problem is. Electronic meters utilize A/D converter, the converter uses Voltage reference, when battery is weak it give faulty voltage reference, as a result you get faulty reading. Do not rely on voltage reading, sufficient voltages do not mean sufficient Battery without enough current in battery.

Sorry if I confuse you, let me try again:

You should check its battery, that's where your problem is. Electronic meters utilize A/D converter. The A/D converter uses bat as Voltage reference, when battery is weak it gives faulty reference, as a result you get faulty reading. Change the battery with fully charge.

Actually, a semiconductor device similar to a Zener diode is used as the voltage reference. But the battery has to be at or above the device's threshold to provide a stable reference.

I put a brand new battery in it, the symptoms are unchanged.

Do you have a 77 or was the 79 a typo?

The 79 was a typo, I have a 77, and I ordered an 87, I'm full of typos lately. I really liked the 77, aside from its lack of true RMS, it did everything I ever asked it to, I hope the 87 lives up to what I've come to expect.

I have an old 77. Serial number 4333xxxxxx. Still works like a charm. Zeros out on any setting. Wouldn't mind having an 87 and keeping the 77 for a backup. Where did you find the best price?

I've found my 77 will work even with a very dead battery. Dead meaning by the old taste test. Probably 6 volts or so.

Is the fuse intact?

I assume so, I didn't do anything that would blow it, but other times the fuse has blown it has not exhibited any unusual behavior. I know what I'm doing, I tried all the simple stuff, something has failed.

Ebay, they tend to go for about $160 used and in good shape, closer to $300 new. There's several different models of 87, make sure you know which one you're getting.

Correctly, the zener (or an IC reference circuit) are part of the A/D circuit. You cannot design a complete A/D without Voltage Referencing.

Jack....

it

scaling

frequency

perhaps

If the fuse is blown you get a consistent reading of about 1 per cent of the true reading.

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