Fluke 17B+ continuity piezo broken? - Page 1
Forum section: electronics / general

author: MrZeroo00
author_rank: Contributor
timestamp: October 10, 2016, 05:27:39 pm
content: Hello,I ordered a Fluke 17B+ on GearBesthttp://www.gearbest.com/measurement-analysis/pp_153177.html?currency=USD&gclid=CjwKEAjwrcC9BRC2v5rjyvSbhWASJACKkjDzRjOdyjyGbRRgwBJwit2B5iZYJn3Nq2cCTDuhAhCXKRoC1tjw_wcBand the beep when there's continuity is not working.It worked for a little bit and then stopped. Did anyone had this problem before? Does it involve changing the piezo buzzer?Thanks!

author: retiredcaps
author_rank: Super Contributor
timestamp: October 10, 2016, 05:43:22 pm
content: I don't have this model. Some comments/questions.Q1) have you tried fresh batteries?Q2) when on continuity, does the display shows 0.00 with the probes shorted?Q3) have you measured something high voltage recently?

author: Zermalmer
author_rank: Regular Contributor
timestamp: October 10, 2016, 07:58:56 pm
content: Beside the questions of retiredcaps...Maybe the buzzer slipped out of position?I have seen this in other models after someone must have dropped the device a little bit harder without any damage.

author: MrZeroo00
author_rank: Contributor
timestamp: October 17, 2016, 12:03:03 pm
content: Thank you for your suggestions!Q1) Yes I swapped the batteries with brand new ones and it didn't fix the problem.Q2) Yes it does show a 0.00 with the probes shorted.Q3) I haven't!Zermalmer, I opened it, there's no obvious damage, I haven't dropped it recently. I recently took the plane with the multimeter though I'm not sure how it would affect it...

author: retiredcaps
author_rank: Super Contributor
timestamp: October 17, 2016, 04:06:39 pm
content: Let's see clear focused pictures of your Fluke 17B+ PCB with two compositions. One is overall and another with a close up of buzzer area.

author: ModemHead
author_rank: Frequent Contributor
timestamp: October 18, 2016, 02:23:53 am
content: Do you have a scope? Short the probes in continuity mode and look for a square wave on the piezo terminals. If you don't have a scope, another DMM in ACV mode should indicate the presence or absence of the signal. I don't have this model either, so I'm assuming the sounder is not one of those self-contained buzzer thingies.

author: MrZeroo00
author_rank: Contributor
timestamp: October 28, 2016, 10:18:23 pm
content: I finally got time to get back to this.I tried to measure some good known resistors and notices that most of the times the readings are completely random and far off from where they're supposed to be. I can't trust this device and don't want to void any warranty, I contacted GearBest support and I'm waiting for them to answer.I'll keep you posted with any progression on this issue. Thanks for your suggestions!

author: tautech
author_rank: Super Contributor
timestamp: October 28, 2016, 10:23:23 pm
content: Quote from: MrZeroo00 on October 28, 2016, 10:18:23 pmIs the buzzer on the PCB or in the case with leaf contacts touching the PCB ?Maybe they need a clean ?

author: grifftech
author_rank: Frequent Contributor
timestamp: November 09, 2016, 05:11:27 am
content: Quote from: MrZeroo00 on October 17, 2016, 12:03:03 pmcarry on or checked baggage?

author: MrZeroo00
author_rank: Contributor
timestamp: November 10, 2016, 02:37:29 pm
content: Since 45 days passed, GearBest suggested a few options.1) I pay for 70$ for the shipping and repair. For a 100$ meter it's not reasonable...2) Refund 30$ on my GearBest wallet which is the option I chose.So I'll attempt repairing this meter. Here are some pictures of the PCB:And a zoomed-out view of the PCB:I measured the signal sent to the buzzer when there's a continuity detected (0.0 Ohm shows on the multimeter screen):I was quite surprised by this waveform, I was expecting a square wave. The amplitude of the signal seems variable and quite low to me.Quote from: grifftech on November 09, 2016, 05:11:27 amChecked baggage but it was in-between my clothes so I think it was well protected.Quote from: tautech on October 28, 2016, 10:23:23 pmThe buzzer seems to be soldered on the PCB.

author: retiredcaps
author_rank: Super Contributor
timestamp: November 10, 2016, 06:46:57 pm
content: Quote from: MrZeroo00 on November 10, 2016, 02:37:29 pmYes, many sellers know this and take total advantage of this.QuoteCheck the soldering on the other side.Here is the relevant part of the leaked Fluke 17B schematic. Check VSS?

author: MrZeroo00
author_rank: Contributor
timestamp: November 10, 2016, 08:10:16 pm
content: Soldering on the other side looks ok. I added redid the soldering to make sure.Awesome, I didn't know about this schematic. Check VSS against what ?

author: retiredcaps
author_rank: Super Contributor
timestamp: November 10, 2016, 08:45:09 pm
content: Quote from: MrZeroo00 on November 10, 2016, 08:10:16 pmVSS with respect to COM jack.

author: ModemHead
author_rank: Frequent Contributor
timestamp: November 10, 2016, 09:40:31 pm
content: FS9721_LP3 datasheet doesn't say much about the beeper output from the chip, other than it's 2.7kHz. I would assume a 3Vpp square wave with 370usec period. The transducer is apparently a dynamic mini-speaker, not a piezo.Your scope shot shows about the right period, the positive half of the cycle is okay but what should be the negative half is not there. Maybe the beeper output is single-ended (needs a pull-down) and the speaker has failed open.Check that one of the speaker's terminals has a hard connection to the negative battery terminal (VSS). I assume the voltages are okay because the meter works otherwise, correct?If you are able to remove the speaker safely, you should be able to get to the bottom of this quickly.

author: MrZeroo00
author_rank: Contributor
timestamp: November 11, 2016, 09:10:38 pm
content: Thanks for your feedback guys! I tried to remove the buzzer with a hot air gun pointed at the leads and the epoxy casing broke causing the leads to separate from the buzzer. I was really gentle, I'm not sure what happened there...Anyway, the signal looks better on the scope (except the weird amplitude but I can see that caused by the fact that there is no load?):I'm thinking of replacing the buzzer by one of these two (both mechanically ok) :http://docs-europe.electrocomponents.com/webdocs/1168/0900766b81168602.pdf: amplitude ok, resonant frequency a little bit off but looking at G(f) it should be loud enough.http://docs-europe.electrocomponents.com/webdocs/141f/0900766b8141f87f.pdf: max. amplitude low but perfect resonant frequency.Do you have any toughts on the replacement parts?

author: ModemHead
author_rank: Frequent Contributor
timestamp: November 11, 2016, 10:05:25 pm
content: Links are bad above, extra colon at the end...Add a resistor (say about 1K) across the terminals (or the scope probe) and hopefully it will look like a square wave.Your choice number one looks OK to me. The second one has a 6.5 ohm nominal coil resistance. I'm guessing this will probably be too low for the chip to drive directly without an external transistor, as shown in the FS9721 data sheet example for "low resistance buzzer".

author: MrZeroo00
author_rank: Contributor
timestamp: November 16, 2016, 10:44:13 am
content: I replaced the transducer with the first one in the list, it works perfectly now.I'm not sure how/why the original one got faulty.Anyway it's fixed now, thanks all for your help !

author: evava
author_rank: Regular Contributor
timestamp: November 16, 2016, 01:44:45 pm
content: And what about this?Quote from: MrZeroo00 on October 28, 2016, 10:18:23 pm

author: grifftech
author_rank: Frequent Contributor
timestamp: November 16, 2016, 02:58:34 pm
content: Quote from: evava on November 16, 2016, 01:44:45 pmoff by the same amount or percent?

author: MrZeroo00
author_rank: Contributor
timestamp: December 06, 2016, 10:08:39 pm
content: Well after full reassembly and putting back the screws it seems to be working fine again. I checked the values measured against a known good multimeter...