FLUKE 179 Repair Info incl. partial Parts List

[icezebra]

Some things I know about the FLUKE 179:
1) There are 4 SOT-23 devices connected to each other near the big DALE power resistor.  On some vintages these are transistors.  On othe vintages they are Schottky diode BAL74.  Either way only one junction per device is used and they are configured as a full wave bridge.
2) The LT Part with the 24351 marking is actually an of the shelf LTC2435 24Bit Sigma-Delta Analog to Digital Converter. The tiny part LTPZ is an LT1790 Voltage reference. (I stole this info from another post)  eevblog.com/forum/testgear/fluke-179-teardown-photos/
3) Here is a partial parts list.  Note: There are no component designations on the PCB. Note: I have seen the MOSFET Q7 and MMBT6419 Q5  destroyed:

[icezebra]

The list in the previous post should say P-FET not N-FET.  Here is some more FLUKE part info (not necessarily related to FLUKE 179):

Fluke Part number:
821637  = Freescale SMBT1388T1  25V NPN
742676  = MMBT3904 60V NPN
820902   = MMBT5089,30V,NPN,50MA
742684   = MMBT3906,40V,PNP,200MA
821637   = SMBT1388LT1, NPN
887179   = SMBT1531LT1, PNP
830489   = BAS16 Diode
851659   = BAV74
1641929   = P-Chan MOSFET IRLML6302 20V 780mA 600mOHM 540mW SOT-23
742320   = BAV99

The MOSFET marking code is very tricky.  I spent days looking for marking code "CJ" but it turns out that the J is just part of the date code.  Here is the datasheet showing how marking works.  The only relevant letter is the C!

www.infineon.com/dgdl/Infineon-IRLML6302-DataSheet-v01_01-EN.pdf?fileId=5546d462533600a4015356688c702627

The MOSFET IRLML6302 does show up in this search engine with a single letter code search:

https://www.random-science-tools.com/electronics/SMD_markings.php?formtype=SMD_markings_search&search_string=C

Also the third letter on the marking has and underscore and overbar (CJU) which allowed me to confirm its identity.

Marking code detective work:

smd.yooneed.one/
embedeo.org/smd_codes/
www.random-science-tools.com/electronics/SMD_markings.php
www.marsport.org.uk/smd/mainframe.htm
www.formatecauto.com/wp-content/uploads/2015/03/tabela-de-equivalencias-transistores-1-EFREN.pdf

[icezebra]

Here is a photo of the "mystery" marking code that turned out the be the IRLML6302.  Note that the remaining two marking code digits were obliterated.

[Doan nguyen]

Kết quả dịch
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i need a schematic of fluke 179 or something like that. my fluke turned on 179 - - - -.i don't know of any faulty parts that could cause this

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[icezebra]

Kết quả dịch
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i need a schematic of fluke 179 or something like that. my fluke turned on 179 - - - -.i don't know of any faulty parts that could cause this

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Hi Doan,

Are you saying your Fluke 179 will not turn on?
Or are you saying it will turn on but no display?
Or what are you reporting is the problem exactly?
 
I can tell you that there are very few active parts on that meter.  If the main chip is OK (which you can determine after a successful power-on by observing the display for the 179 Splash Screen) then it is easy to repair.  You can check all the active devices with a meter in situ (Diodes, BJT, FET, voltage regulators), and if you have the inclination, you may replace the LTC2435 24Bit Sigma-Delta Analog to Digital Converter, although I bet there is nothing wrong with it.

See the parts list I posted above, as well as the other URL I referenced, for the details on the active devices on the PCB of the 179

In my experience the problem was with the power control MOSFET and associated BJT.
MOSFET Q7 IRLML6302 and BJT Q5 MMBT6419.  (Note that there are no component designations on the PCB, but I posted a photo above to help with identification)
I suspect the power-on circuit cannot defend itself against battery polarity error.  Which, if true, is pretty appalling.  Looking at YOU FLUKE!

Regarding a schematic...if you ever find one, let us all know!

[Kaluluka]

Regarding a schematic...if you ever find one, let us all know!

I had problem with 179 (bought on EBAY as fully working unit!) actin up on arrival in March this year (had no time to check at the time of arrival) and last week I finally got time, but it was now only showing "batt" in any settings after switch on. I read lots of info here on the forum and many other forums, regarding repair, and discovered user (on this forum) who maybe could help me with service manual for 179 (same as 77 IV). after writing to him directly, he did share with me original FLUKE 77 IV SERVICE MANUAL: Man was that big help! I fixed my FLUKE 179 same day as I received service manual. Culprit was ASIC chip, which I suspected from the beginning, without checking (because how multimeter acted upon arrival!) PCB for Brocken parts and had ASIC chip already delivered from China in advance. I was skeptical about that chip being fake, but after close examination under microscope, decided to replace it on PCB, because it had same dot errors on the chip writing silkscreen as original: same place, same kind of silkscreen printing error.
Like said above: fluke 179 is working now. I just have to replace shorted Q3 (next to COM connector) which is out of PCB for now.

Regarding SERVICE MANUAL: please do not ask me to share it, because it is not from me and I do not want to upset original owner.
You can try to search that user and ask him yourself, like I did.
I hope you all understand that.
Regards,

[icezebra]

Regarding a schematic...if you ever find one, let us all know!

Regarding SERVICE MANUAL: please do not ask me to share it, because it is not from me and I do not want to upset original owner.
You can try to search that user and ask him yourself, like I did.

I did, thank-you very much for the tip!  The schematic cleared up my assumption that the power circuit is not properly protected from a reversed battery. On my meter, the protection diode CR3 was missing completely!  It is supposed to be next to the plug for the battery connector. It is a GF1B.  Link below. Anode connects to Battery Minus.   

If anyone needs a source for U2 I recommend https://www.utsource.net/pro/LTC984-1CG-ES.html  I have had good experience with them providing genuine parts.  Also, if the unit will not power up try replacing Q7 and Q5 as I describe above.  Regarding the 4 SOT-23 devices I mentioned above, turns out they are NPN BC817 25V 500mA General Purpose BJT.  Connected as back-to-back diode protection on two different ASIC inputs, Pin 36 ISRC and Pin 1 SENSE.

If anyone has the datasheet for U1 (LTC984-1, LTC984-1CG-ES) please post or share.  If anyone has a clear photo of the right hand half of the schematic on page 44 of the Fluke 77-IV/BN Service Manual  (Figure-8) please also share it.  Thank-you.

GF-1B Datasheet:
https://rocelec.widen.net/view/pdf/uxqpnlhldz/ONSM-S-A0003589161-1.pdf?t.download=true&u=5oefqw