Trying to identify 2 missing components on PCB of a Huawei smartwatch. - Page 1
Forum section: electronics / repair

author: snowzord
author_rank: Contributor
timestamp: May 29, 2020, 08:56:18 pm
content: Hi!I have this Huawei Smartwatch, model W1 or Classic (have seen both names).The smartwatch works, but only when it's charging. It charges, but it gets very very hot to the touch.If I unplug it from the charger, the smartwatch will endlessy reboot until it has no battery left. The battery drains very fast.Replaced the battery with a brand new one, from Huawei, but I still have the same problem.Upon disassembling the smartwatch, I identified two missings components on the PCB. This 2 components, are the one's that I circle around on the following image (one on each line):So, some more help: I tried my best to collect all the info that my knowledge permits, and found out that this 2 components are both on 2 3v lines, one component missing on each line.This 4 lines (ground, 5.7v, 3v and 3v) are the lines that come from the gold pins, these pins make contact with the charging dock to charge the watch.So, can this be the root of my problem?If you guys need any info, I will try to do my best.Thanks for any help, in advance.

author: aqibi2000
author_rank: Regular Contributor
timestamp: May 29, 2020, 09:27:57 pm
content: Yes this can be the cause of the battery.They can be used for the battery gas gauge if you search iphone you’ll see similar reboot loop instances.Get some clearer photos of the required components. One will be a cap and the other a resistor from iphone repair experience

author: Twoflower
author_rank: Frequent Contributor
timestamp: May 29, 2020, 09:43:53 pm
content: Here are some better pictures of a working specimen:https://www.androidpolice.com/2015/09/17/teardown-it-very-much-looks-like-the-huawei-watch-has-a-speaker-inside-it-but-it-doesnt-do-anything-yet/It looks like two caps. The values of the caps is not readable on the pictures (if there are any values printed on them at all).

author: snowzord
author_rank: Contributor
timestamp: May 29, 2020, 09:54:01 pm
content: Quote from: aqibi2000 on May 29, 2020, 09:27:57 pmThanks for the help. I will try to get clearer pictures.Quote from: Twoflower on May 29, 2020, 09:43:53 pmThanks for the pictures.Two caps, OK. From what I can read on mine, the only thing printed on top, of the one's that look identical on the side, it's "MW".It's there any way I can measure the value using a multimeter?

author: Twoflower
author_rank: Frequent Contributor
timestamp: May 29, 2020, 10:11:03 pm
content: Depending on the multimeter: Yes. Some can measure the capacitive value.On a second thought it could also be diodes for protection. The Pogo-pins are the connector to the USB-connection for charging? If yes, that is more likely protection diodes as it seems that they are connected to the data lines.Most multimeters has the capability to measure diodes. Usually using the continuity mode. On the display they show then the voltage drop. In one direction it should display overload (too high resistance) and in the other 0.3...0.8mV (depending on the diode-type) if that's a normal diode.

author: snowzord
author_rank: Contributor
timestamp: May 29, 2020, 10:27:01 pm
content: Quote from: Twoflower on May 29, 2020, 10:11:03 pmThat's what I tought. Mine is one cheap version from UNI-T (UT33C) from what I check, it doesn't have.Yes, the pogo-pings are the connector for the USB-connection for charging.In diode mode, measuring the diode on the board, on one direction I get the display overload you say and the in the other direction, it shows a value of 172 (it doesnt show mV or anything else, just the number).

author: wraper
author_rank: Unknown
timestamp: May 29, 2020, 10:31:08 pm
content: Look like TVS diodes for ESD protection. One with 4 or 5 terminals should be either multiple TVS in one package or pass through type. Something like this:https://datasheet.octopart.com/IP4059CX5/LF%2C135-Philips-datasheet-14043957.pdf

author: snowzord
author_rank: Contributor
timestamp: May 30, 2020, 09:04:16 am
content: May I ask:For testing purposes, making a bridge between the pads of the missings diodes will work to test it out?

author: Twoflower
author_rank: Frequent Contributor
timestamp: May 30, 2020, 10:38:16 am
content: Quote from: wraper on May 29, 2020, 10:31:08 pmThey would make sense there. But it looks like normal two terminal devices. Also the PCB traces wouldn't match to the 5-Terminal protection devices.Quote from: snowzord on May 30, 2020, 09:04:16 amNo! That would create a short between the GND and the data lines. Don't bridge them. Actually if these missing parts are diodes open as it is right now should do no harm except that the USB interface is more sensitive against over voltage/ESD. I doubt that the missing parts there can cause the problem you describe. As they probably are there for protection of the USB interface.

author: snowzord
author_rank: Contributor
timestamp: May 30, 2020, 10:53:00 am
content: Quote from: Twoflower on May 30, 2020, 10:38:16 amGood to know, thanks for the info.What I think it's happening, it's that, since you said that without the diodes, the USB is more sensitive to over voltage, that may be causing the excessive heating, and the excessive heating may be causing the reboots. Am I thinking right?

author: wraper
author_rank: Unknown
timestamp: May 30, 2020, 11:00:50 am
content: Quote from: Twoflower on May 30, 2020, 10:38:16 amOne in the middle is different. And IMHO looks like it has more than 2 terminals. How many there actually are is not clear since there are remains of the part which need to be desoldered to see the actual pads.

author: snowzord
author_rank: Contributor
timestamp: May 30, 2020, 11:13:56 am
content: Quote from: wraper on May 30, 2020, 11:00:50 amNo, it has 2 terminals for each diode only.

author: wraper
author_rank: Unknown
timestamp: May 30, 2020, 11:35:51 am
content: Quote from: snowzord on May 30, 2020, 11:13:56 amLooked at better picture and yeah, it's the same. Should be like this:https://m.littelfuse.com/~/media/electronics/datasheets/tvs_diode_arrays/littelfuse_tvs_diode_array_sp3145_datasheet.pdf.pdfBut they are not essential for operation. They do nothing unless ESD discharge happens.

author: Twoflower
author_rank: Frequent Contributor
timestamp: May 30, 2020, 11:55:09 am
content: Quote from: snowzord on May 30, 2020, 10:53:00 amNo, your assumption is not quite right. The diodes protect the data lines as they are sensible. So no real protection of the power supply lines. For the USP power protection usually there's a poli-fuse. Either there is none or it is on the back-side of the PCB. As they are usually reasonably huge I wouldn't wonder if there is no fuse build in.Even as the missing parts are not a good sign I think the 'real' problem isn't there. My bet would be more to the battery itself or the power management compartment (charging/power supply for the watch).

author: wraper
author_rank: Unknown
timestamp: May 30, 2020, 12:21:32 pm
content: Quote from: Twoflower on May 30, 2020, 11:55:09 amUsually it's a regular SMD fuse, not poly-fuse. Also USB power line usually has TVS on it as well. Otherwise I agree with you.

author: snowzord
author_rank: Contributor
timestamp: May 30, 2020, 01:38:35 pm
content: Quote from: Twoflower on May 30, 2020, 11:55:09 amGot it.I think that it would be very strange for a brand new huawei branded battery to fail like the one that was on the watch when I bought it, which had a lot of use.About the "power management compartment" for the watch I'm using a Huawei branded one that I bought to try to find the problem, since the clock came with a aftermarket one and it could be the problem. But I was still facing the same problem.Today, I remembered that I was charging the watch with a fast charger and tried with a low power one (5V 1A) in hope that it was something with the fast charge, but no fix.EDIT:Well, now i'm even more confused.If I get the watch outside of the charger but if I work with it (scrolling through the menus, change settings) it stays OK and alive. Right when I stop, after 10/15 seconds it reboots.lol

author: Twoflower
author_rank: Frequent Contributor
timestamp: May 30, 2020, 03:30:18 pm
content: Wit the power compartment (I should have more precise) I actually meant the watch internal power management that regulates the charge of the battery, generates the required voltages for the individual components and so on. And the last observation actually indicates that there is something wrong. Keeping the watch busy requires higher voltages for the components (CPU, display...). And that seems to work. After some idle time the components fall into low power mode and the power management reduces the voltages of certain supply rails. That seems to cause the trouble.One of my wild guesses would be that there are some more parts missing/damaged. For example a capacitor that cleans the supply voltages. Under the reduced voltage situation the components could be more sensitive to noise on the supply rails. A missing cap here could cause that. But that would normally not explain the overheating situation you face. Unless there is more...

author: wraper
author_rank: Unknown
timestamp: May 30, 2020, 03:44:30 pm
content: Forgot to mention that those TVS diodes with 99% probability were broken by you when you were taking the watch apart and have nothing to do with initial fault. They are very fragile when poked since they are basically bare silicon dies.

author: fzabkar
author_rank: Super Contributor
timestamp: May 30, 2020, 07:41:44 pm
content: Quote from: wraper on May 30, 2020, 12:21:32 pmIME, at least in desktop PCs, the protection is usually provided by a polyfuse, polyswitch, ie a resettable device. In fact that makes much more sense than a fuse that goes open and renders the device inoperable.

author: fzabkar
author_rank: Super Contributor
timestamp: May 30, 2020, 07:43:22 pm
content: Quote from: wraper on May 30, 2020, 03:44:30 pmIt may be that these are optional components that were omitted during manufacture.

author: wraper
author_rank: Unknown
timestamp: May 30, 2020, 07:50:31 pm
content: Quote from: fzabkar on May 30, 2020, 07:43:22 pmWhen there are leftovers of components remaining on the pads?

author: wraper
author_rank: Unknown
timestamp: May 30, 2020, 07:58:27 pm
content: Quote from: fzabkar on May 30, 2020, 07:41:44 pmDoes not happen on high power rails. If there is a fuse, it's not resettable because 10A polyfuse is not something small and with low heat dissipation. If it's on VUSB, it's understandable to use polyfuse because you don't want to permanently damage USB port on host device because of faulty sink device attached. On sink device there are different considerations. If fuse blows, it's because device was faulty by itself or something gone horribly wrong with VUSB.