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Electronics => Projects, Designs, and Technical Stuff => Topic started by: rstor22 on July 10, 2015, 11:53:31 pm

Title: Fluke 8012A - No AC Reading
Post by: rstor22 on July 10, 2015, 11:53:31 pm

I purchased a used Fluke 8012A today. DC voltage/current, and ohms read ok. When testing AC it indicates over range for all ranges.
Would the U8 true RMS converter (see attached picture) be the sensible place to troubleshoot? 

Title: Re: Fluke 8012A - No AC Reading
Post by: rstor22 on July 11, 2015, 02:51:27 am

I believe my LM3046N is bad. I tested it in circuit, was unsure, however after reading:

https://www.eevblog.com/forum/repair/fluke-8050a-true-rms-u32/25/?wap2 (https://www.eevblog.com/forum/repair/fluke-8050a-true-rms-u32/25/?wap2)

I decided to remove the 3046 and test out of circuit.

PIN 13 (Emitter) + to PIN 14 (Collector) - reads approx. 30 mega ohms.  Diode check of emitter (PIN13) to collector (PIN14) reads .626V.
Therefore I would take it that the transistor is bad within the 3046?

The data sheet for the 3046 indicates:
"The collector of each transistor is isolated from the substrate by an integral diode. The substrate (terminal 13) must be connected to the
most negative point in the external circuit to maintain isolation between transistors and to provide for normal transistor action."

So I am unsure of the readings for PIN 13 and PIN14 above are normal?


Unfortunately I was unable to desolder the 3046 (do you have to do something special as this is a hybrid ceramic board?) and decided to cut the legs and in the process lifted some pads...  :-BROKE

Title: Re: Fluke 8012A - No AC Reading
Post by: rstor22 on July 11, 2015, 02:58:22 pm

I checked my Fluke 8050A which has a similar hybrid ceramic. Diode check of emitter (PIN13) to collector (PIN14) reads .626V for the LM3046 however resistance shows open between these pins.

Would it be safe to conclude that the 38 mega ohms reading from PIN 13 (Emitter +) to PIN 14 (Collector -)  for the LM3046 in my Fluke 8012A indicates it is bad?

Title: Re: Fluke 8012A - No AC Reading
Post by: rstor22 on July 12, 2015, 02:32:37 pm

My local electronics surplus store had a 8010A for parts that I was able to get for cheap. The '3046 [U8 board] in the 8010A also had a high resistance reading (when tested in circuit) as described above for the 8012A so I am thinking it was another component on the U8 board which was bad.

I ended up removing the U8 from the 8010A parts unit and installing it in the 8012A and now AC measurements work.

Title: Re: Fluke 8012A - No AC Reading
Post by: GreyWoolfe on July 13, 2015, 11:32:54 am

 :-+ :-+ Congrats on the repair.  Enjoy the meter.