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EEVblog 1663 - BM786 Multimeter REPAIR + InEr Error Investigation

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EEVblog:

--- Quote from: mwb1100 on January 27, 2025, 11:14:46 pm ---Interestingly, as far as I can tell the 87V Max is identical to the 28II other than the name.  Its list price is $100 less - still pretty whopping.
--- End quote ---

Yes, same meter. Just marketing having a wank.

Kleinstein:
A photo-interrupter would need quite a bit more power. It would be extra effort to turn on / off to save power.
A relatively easy way around would be using a little more current and turn off the test current when the meter is actually in the µA range. The test current would than not interfere with the sensitive measurement ad when in the amps more it is not longer important to detect the connector.

Another solution is a mechanical lock: block the terminals when not in amps mode or maybe a 2nd off position at the other end.

ballsystemlord:

--- Quote from: Kleinstein on January 28, 2025, 08:42:08 am ---A photo-interrupter would need quite a bit more power. It would be extra effort to turn on / off to save power.
A relatively easy way around would be using a little more current and turn off the test current when the meter is actually in the µA range. The test current would than not interfere with the sensitive measurement ad when in the amps more it is not longer important to detect the connector.

Another solution is a mechanical lock: block the terminals when not in amps mode or maybe a 2nd off position at the other end.

--- End quote ---

You mean, gasp, we might actually get bigger batteries in our DMMs than AAA cells? ;)

floobydust:
Optical jack-sense is used on the Fluke 287, 189/289.
Surprisingly it's not super reliable, people break the IR LED or phototransistor somehow.
They are oddball, right angle-looking Osram parts.
The input jack can break one of the two pins as well.
https://www.eevblog.com/forum/repair/fluke-289-shows-message-warning-leads-connected-incorrectly-i-have-detected/
https://www.eevblog.com/forum/repair/fluke-289-lead-detection

EEVblog:

--- Quote from: ballsystemlord on January 28, 2025, 05:37:24 pm ---You mean, gasp, we might actually get bigger batteries in our DMMs than AAA cells? ;)
--- End quote ---

The 121GW originally had AAA cells, but I decided to make the case thicker to accomodate AA instead.

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