Electronics > Repair
Fluke 73 III repair
<< < (3/4) > >>
bborisov567:
I dis some cleaning and let it dry for a few days. Now with the input floating i get OL reading but with the input shorted it get around -9 ohms. What does that minus mean? Does it mean there is a higher voltage on the OHS pin than expected?
Paceguy:
Maybe during the cleaning process, the calibration pot got turned. I would check to see if the DC calibration is spot on first. There is just one cal pot on these.
bborisov567:
I already recalibrated it an works fine and accurate on DC with the exception of some small voltage reading (0.2-0.3v) when the input is floating. But when it is shorted i get a solid 0.00 v reading.
marcovanyken:

--- Quote from: bborisov567 on July 27, 2023, 06:52:20 pm ---I got the unit with leaked battery. Fortunately there was little damage to the board. I cleaned the board very well, even removed the analog chip and cleaned under it. Now the unit is in somewhat better condition but still there is a problem with the ohm meter function. In open circuit it reads about 8-10 megaohms and when shorted it read about 40 ohms and the value is gradually going to zero, it's like there is a charging capacitor. All other modes are working accuratelly. When measuring voltage it needs about 3-4 seconds to settle. I tried removing the MOVs at the input but there is no change. Also when i short the "OHMS" pin to ground it reads around -40 ohms, note the minus. The 33pF cap between OHMS pins and ground is changed. The refference voltage and the supply voltages are also stable. I don't have the exact schematic but i've been using the schematic for the 73 ii, which is quite similar. I have checked Q1,2,3 with a transistor tester and they look okay.  Can somebody suggest what might be wrong? |O

--- End quote ---

Hi Bborisov,

I see this is an old thread but hopefully you receive my message.
Can you perhaps tell me what Transistor is the one marked in my attached pic. Its the pic of your board but I have the exact same board.

Thank you
mqsaharan:

--- Quote from: marcovanyken on November 11, 2024, 10:03:31 am ---
Can you perhaps tell me what Transistor is the one marked in my attached pic. Its the pic of your board but I have the exact same board.


--- End quote ---

I don't have the service manual or schematic for this particular meter. But my guess is the encircled transistor will be 2N3904, exactly the same as the one next to it. Together these are used as a high speed clamp.
Please be careful while taking my suggestion. I could be completely wrong.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod