Electronics > Repair

Fluke 289 not quite sorted.

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nixxon:
Commongrounder: I really dont know how the «current terminal sensing» works. There are two components (Q24 and Q27) «looking» at each other across both terminal cavities. I would, with my limited electronix knowledge, assume that one side was active and the other was passive. However, both Q24 and Q27 are active components. I even dont know if the terminal sensing discriminates between the two current terminals. I will have to check it out when I get home tomorrow. For all that I know, the DS2 component may register an inserted probe jack and is able to discriminate between the two current terminals throug differently coded signals missing from either Q24 or Q27 when a jack is inserted.

If someone more experienced could share his or her thoughts about how the optical current terminal sensing works in the Fluke 287/289, I would surely be happy to read about it...

commongrounder:
So, I own a 289, and took a peek through the current jacks (not inclined to disassemble it at this time as I’m using it today). I can see a clear plastic prism reflector between the current jacks that appears to be part of the molded plastic jack frame. The light isn’t visible, but I have a small infrared probe which detected IR light in the jack cavities. I believe the diode is an IR LED, and the two outer devices are IR photo transistors. I was able to prove this, as well as understand the reasoning, by trying different combinations of plug insertions. The beeps are in conjunction with an on-screen warning of improper lead positioning. 1) Warning when lead(s) are inserted in current jack(s) in any mode but current measurement modes. 2) Warning when lead is not inserted into one or the other current jack in current measurement modes only. 3) Warning when plugs are inserted into *both* current jacks at the same time, in current measurement modes. Obviously, 3) is not a proper lead configuration for any purpose. This can only be discerned with two independent optical sensors.
Hope you can get the display up and running again. Best of luck.

nixxon:
Aha, so the tiny guy in the middle (DS2) is the active part and the powered Q24 and Q27 are the sensors? Wow, My mind was set the other way around. The «optical» part of DS2 looks so small. But the transparent top edges of DS2 are angled 45 degrees both left and right and would transmit both ways towards both Q24 and Q27, across both cavities.
[EDIT: Actually there is a transparent optical path between the two A - mA/uA input jacks. The top surface of the DS2 touches the middle of the optical path surface.]

ElecSeb:
Q24 & Q27 = SFH 325 FA-3/4-Z - SIDELED® Silicon NPN Phototransistor in SMT SIDELED®-Package
DS01 = SMD LED (exact type unknown atm)

nixxon:

--- Quote from: Yakuzza on November 26, 2017, 12:40:33 pm ---(...)
In addition, which I didn’t mentioned this at the beginning, there was a bit of greenish dried fluid marks in on PCB close to Amper input (between the two left input jacks) and similar thing on the top corner of the LCD, close to the soldered wires. I’ve clean it but found no source.
(...)

--- End quote ---

Very interesting information about the LCD top corner... I will check it out next...

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