Fluke 179 dead after replacing fuses - Page 1
Forum section: electronics / repair

author: paulbt
author_rank: Regular Contributor
timestamp: October 17, 2021, 05:24:30 pm
content: Hello!Last week I borrowed the dmm from my work colleague. Initially I checked some DC voltages and some resistances on a board, everything was as expected. Then I needed to check the overall current consumption of the board (few hundred mA), but the 11A fuse was already dead. So I turned it off, disconnect the battery, open the case, replace both fuses actually because both were dead. Then put everything back with care and...surprise...the dmm was dead, nothing on the display no matter the position of the rotary switch, no light, no power-up options, no beeps when pressing the buttons. I was never expecting that on a "lifetime warranty" Fluke.I took it home and promised to repair it. First I checked if the battery voltage was present on the board...it was, so the battery clip + wires + pcb connector are ok.Then I checked for broken/corroded traces, broken solder joints, burned components...nothing so far.The range switch spring contacts are just fine and there are no heat marks anywhere.Then I searched here on the forum for repairs of 175, 177, 179 and 77IV models. I got a few hints to check myself, but still no success. The power supply module seems to be ok - I get one 3v3 and two 5v outputs.I tried to supply it with a bench PSU and I noticed that there is no current consumption, not even 1mA.If you have any ideas on what I should further check, please let me know...

author: TonyBe
author_rank: Regular Contributor
timestamp: October 17, 2021, 07:02:41 pm
content: Hi,have you checked if the DMM really is not turning on? I.e. if the zebra strip or the display has gone wrong during the replacement, you wont get anything on the display but the meter might be fine. Check it by turning the meter on and press some buttons. I expect it to beep (since most DMMs has this feature). Another way would be to short the terminals in continuity mode...RegardsTony

author: paulbt
author_rank: Regular Contributor
timestamp: October 17, 2021, 08:36:38 pm
content: Quote from: TonyBe on October 17, 2021, 07:02:41 pmHi,Today I assembed everything back and tried this, hoping for some luck...but no. So the statement from my first topic "nothing on the display no matter the position of the rotary switch, no light, no power-up options, no beeps when pressing the buttons." still holds up. I don't know if the buzzer is working properly, but it looks intact and it's golden spring contacts are just fine.

author: Nusa
author_rank: Super Contributor
timestamp: October 18, 2021, 06:35:02 am
content: It may sound crazy, but try undoing what you changed. Take the fuses out again.

author: paulbt
author_rank: Regular Contributor
timestamp: October 18, 2021, 06:59:57 am
content: Quote from: Nusa on October 18, 2021, 06:35:02 amWhat I have tried so far was troubleshooting on PCB+battery/PSU without fuses without display. Then general functionality check fully assembled also without fuses. To be honest...I was expecting more advanced troubleshooting tips so far, not that type of "sir, have you plugged in your device?"Can it be something wrong with the main IC TI M430F437? I also tried to short the battery terminals (without battery) as someone said in an older Fluke repair topic, but it was not helpful.I can't find out what this meter has experienced before I got it and neither we can send it for warranty, so I will continue to try to repair it.

author: xavier60
author_rank: Super Contributor
timestamp: October 18, 2021, 10:01:44 am
content: Basic checks for any MCU are Power , Reset and Oscillator. Also, it is capable of being asleep. One has to find which pins to check.A sleeping MCU usually has both OSC pins locked to the same logic state.Is there voltage present across the press switches' contact pads?

author: abdulbadii
author_rank: Frequent Contributor
timestamp: October 18, 2021, 02:29:45 pm
content: "check the overall current consumption of the board (few hundred mA)"First most, clarify ithow can the dmm test current if is open by cut fuse

author: shakalnokturn
author_rank: Super Contributor
timestamp: October 18, 2021, 06:34:23 pm
content: After checking MCU power, reset, oscillator, check for serial bus activity.

author: TonyBe
author_rank: Regular Contributor
timestamp: October 18, 2021, 06:46:44 pm
content: Quote from: paulbt on October 18, 2021, 06:59:57 amIt is pretty hard to get you more advanced tips when the failure mode is that basic. When the voltages are present and the DMMs is really do nothing as you mentioned, one can only check for activity on the ICs (as mentioned from above).Check for crystals (I can see one on the picture, although this seems to be a LF crystal), measure the current consumtion of the DMM with a nother DMM/ AMM to see if it is plausible. Use a Scope to check the Reset logics of the board.What are you expecting? We do not have any access to the unit, so we need to step through every troubleshoot together before finding the solution.

author: paulbt
author_rank: Regular Contributor
timestamp: October 19, 2021, 08:27:55 am
content: Quote from: xavier60 on October 18, 2021, 10:01:44 amThank you for the hint! This is the type of "advanced troubleshooting tip" I was expecting for. I will search for the datasheet and start to probe some pins with my cheap oscilloscope, maybe I will find something. What do you mean by press switches contact pads? You mean dmm button contact pads?Quote from: shakalnokturn on October 18, 2021, 06:34:23 pmThank you also for the hint, I will check it!Quote from: abdulbadii on October 18, 2021, 02:29:45 pmMy intention was to to check the current consumption of my DUT board (from workplace) with this dmm, but I could not do it because the fuse was dead.Quote from: TonyBe on October 18, 2021, 06:46:44 pmYup, the failure is very basic but strange and highly unexpected for a fluke. And usually it's the basic stuff that kills us (especially during an exam).Thank you for the hint, I will also check the oscillator! This is the type of "advanced" tip I was waiting for. Most of the basic stuff I've already tried and explained them in my very first post.About the current consumption, I usually trust my PSU, it's an Aim TTi PL601 which can measure down to 0.1mA, but I will also measure it with another dmm on mA range just to be sure.

author: xavier60
author_rank: Super Contributor
timestamp: October 19, 2021, 09:15:23 am
content: Quote from: paulbt on October 19, 2021, 08:27:55 amThat's right. Just because it's easy to check. I have had seemingly insignificant clues lead to a fix.

author: MichaelPI
author_rank: Contributor
timestamp: October 24, 2021, 12:21:22 pm
content: Based on the failure description and that you checked the power supply rails already (measure them against the local circuit grounds - GND pin of the chips, to make sure, the voltages are really present at the chips). The 3.3V rail is specifically for the digital portion of the circuit (microcontroller, ...). As basically nothing is operational at all, the microcontroller could be the root-cause. Have you measured the total current consumption of the meter, when it is powered-on?

author: shakalnokturn
author_rank: Super Contributor
timestamp: October 25, 2021, 01:21:27 am
content: Quote from: paulbt on October 17, 2021, 05:24:30 pm

author: MichaelPI
author_rank: Contributor
timestamp: October 25, 2021, 04:50:00 pm
content: This is something I do not really understand. If there is a voltage between the GND pin and the VDD pin of the individual chips, then there must be current flowing into the device. It is unlikely all chips are blown in such a way, the current consumption is zero. That is why, I said, measure those voltage directly at the chip or at least at the bypass capacitors. There are 3 voltage regulators on the PCB (3.3 V, 5 V, 2.5 V), all of them have quiescent current. So I would expect minimum 200 uA, even in case the microcontroller does not power-up.

author: paulbt
author_rank: Regular Contributor
timestamp: November 07, 2021, 11:14:13 am
content: Hi!Update...after 2 weeks not touching the dead fluke, today I decided to grab it and check some MCU pins with the oscilloscope.But first I hooked it to my bench psu set to 9V and a dmm in series to measure mA/uA consumption - surprise - it was alive!Then I put back it's original energiser battery - surprise again - not dead anymore, it shows "Batt", but the battery measures ~7V []After that I replaced it with a new battery of different brand - it works again!Tried again with the energiser - same "Batt" warningSo what is the voltage threshold at which low battery sign appears? Is it 7V? Answer: no, it's about 5.5V -see photos below-It seems like every voltage source is different from the equipment's point of view. It makes me think that a bench psu is somehow not equivalent to a battery, even though both deliver the same stuff (voltage). I very well know they have different output resistances, but I was certain they are equivalent. I will research more on this topic and I will also rewatch the batteriser monkey videos...

author: Per Hansson
author_rank: Unknown
timestamp: November 10, 2021, 07:19:32 pm
content: Quote from: paulbt on November 07, 2021, 11:14:13 amI realize this is not the beginners section but did you measure that battery with the DMM as a load?Because there can be a huge difference in load vs no-load voltage on a battery.

author: TonyBe
author_rank: Regular Contributor
timestamp: November 18, 2021, 03:16:31 pm
content: Hi,regarding the voltage of batteries and lab supply. In some units there is a dedicated load (most commonly a load resistor switched in parallel to battery with a transistor). When the device is turned on, this load is switched on for a short pulse and the resulting batt voltage is measured and checked aginst threshold. The ESR of a lab supply is by no means equal to that of a battery. The batt ESR can be a function of temp, current, age, aso. while the ESR of the lab supply mostly depend on the internal construnction and can be as low as the resistance of the cables that you're using to connect the DUT.If you want to make sure, check the batt voltage with a single shot trigger scope at the moment you're turining on the DMM. If you cannot recreate the same behaviour with the lab supply turned down to 7V, something else will be faulty on the unit.RegardsTony