Silvercrest Wet and Dry Vacuum Cleaner Repair
Recently my brother gave me a defect Silvercrest wet-and-dry vacuum cleaner that no longer worked. Opening the vacuum cleaner was easy after removing 5 screws. Apparently charging the lithium-ion pack still worked. When the 9.6V DC power adapter was plugged in, the dual led under de green power switch showed a red flashing light when the battery was charging, and it showed a constantly green lit led when the pack was fully charged.
But the motor only made ticking movement sounds when the green slide on power switch was activated. And it only briefly worked sometimes when the power adapter was pulled out of the 230V AC socket. Powering the board from an external 8V DC source made no difference.
Next photo shows the charging C- and C+, battery B- and B+, and motor M- and M+ board wiring.
Previous photo also showed the 5 wire flat cable connector to the switch board with duo led. Plus the yellow wire connector that goes into the two 18650 lithium-ion cell pack (likely the temp sensor). Next photo shows this pack and the 7.2V DC motor. Both in good working condition!
Above photo shows the small simple switch board with duo led, with the green ‘battery full’ green led lit. That only lits up when the charging power adapter is connected.
This obviously was all just a boring intro because we now begin with the interesting part of this repair by checking all smd parts and the board circuit. Which was difficult because the most important part of our board was the 14 pins smd controller that had no top marking. That no doubt was removed for copy protection reasons by the manufacturer who wants to keep it secret. That sadly happens too many times in other electronic products too! Which in this case in my opinion would be a good reason to no longer buy any Silvercrest product!
And that is also why I didn’t bother to draw and examine the entire circuit that would be incomplete afterwards anyhow. And the fact that all active diodes, transistors, and mosfets were smd parts only made checking them already more difficult to begin with! Next pictures show a last bottom view of the Silvercrest case with the there placed charging chassis port, and the front cleaning bag side.
Next photo shows the component view of the vacuum cleaner board with the unknown 14 pins smd controller chip. All other part markings were readable. Only a few board markings were hard to read.
I started to desolder the yet unknown triodes (because the 3 character smd code markings on top of the parts are never very decisive. Often just the first same 2 smd code characters give many different smd components as result!).
In following clear enhanced boardview photo I added 2 red stars where I modified the circuit by cutting the two wire connections that represent the 2 switch contacts coming from the switchboard slide-on switch. Because of the here limited A4 page size the resulting photo is sadly a bit smaller than the original picture size was. But I hope it is still clear enough to understand where all tracks and components go and how the Silvercrest was modified now doing exactly what it did before the motor stopped working.
Here follows a BOM list of all controller board parts. Followed by all triode and diode tests I checked with my Peak Atlas DCA75 Pro semiconductor tester and its here very useful Peak Atlas PCA23 test adapter.
Parts in Silvercrest Rechargeable Dry and wet vacuum cleaner SAS 7.4 LI A2, Manufactured 2014-03 Germany. See also photos of measuring all active parts.
Transistors, mosfets and diodes:
DK1 – smd code D1 dual cathode diode
UO1 – TL431 smd
Q2 – Power Mosfet 50N03
Q3,Q4,Q11 – smd code A2 n-chan mosfet
Q5 – smd code A1 p-chan mosfet
Q6,Q7,Q8,Q10- smd code .J3Y npn transistor hfe 264
Q9 – smd code 2TY pnp transistor hfe 296
D1,D2 – diode M4 marking
32 Resistors (not all board text markings could be clearly read!)
See also photo of close up board component view :
R0 – 000
R1,R10 – 471
RI? – 01D
R4(bigger) – 2003
R5 – 30D
R6,R7 – 823
R8 – 01B
R9 – 561
R11,R13 – 01D
R16,R33 – 103
R17,R18(bigger) – 1R0
R21 – 102
R22 – 30D
R31 – 682
Next picture only shows a very quick incomplete handdrawn circuit and all wire connections of this board.
Simply because I had no info on the controller chip. And also because I found an easy way to fix the failing motor problem.
Above photo shows the box that contains the very helpful SOT23 test adapter. Next photo shows this adapter that connects onto the DCA75 Pro.
That sometimes only needs an extra little push on top of the in the adapter inserted sot23 parts under test when they make bad contact because of the old solder that is left on the desoldered triode pins. Which in those cases results in ‘unrecognized’ semiconductors.
Previous photo on the right shows the test result of component DK1.
Above photo shows that the smd part with code .J3Y was a NPN transistor with an hFE of 264. ( .J3Y = J3Y = Npn Ic 0.5A S8050 , J3 = S9013, 2TY = Pnp Ic 0.5A S8550, A1 = AO3401 mosfet, A2 = AO3402 mosfet.)
Next photo shows the results of parts 2TY, A1 and A2. Respectively a PNP transistor with an hFE of 296 (Which is very high for common transistors!), and a P-Channel mosfet, and last was a N-channel mosfet that also tested good!
The test results of these parts with given smd code may now also be very helpful when these are also found on other controller boards!
Now to complete this article here is exactly how this vacuum cleaner was modified:
Sometimes when the adapter was quickly removed from the 230V power line the motor briefly started rotating but right after that stopped working again. And when instead of the battery pack an external 8V supply was powering the controller board the motor still refused to work. And the controller IC is controlling both charging battery pack and activating the motor together with the 431 triode on position UO1. But finding out what part is out of order is close to impossible because there was no IC marking on top of the 14 pins chip given! Maybe a good reason to no longer buy anything from Silvercrest or any other firm that makes servicing much harder!
It could be a defect controller 14 pins dil smd IC or some small resistor failure because most tested transistors and diodes were okay! I used my Gordak 952A hot air station to remove them and used my Ersa MS6000 solder station to solder them back. Most of the triodes I did not have in stock but I simply would have just replaced some of them without the testing to save time if I had.
Successful modification on this Silvercrest wet and dry vacuum cleaner was now done by removing the switch board wire connections from the 5 wire flat cable to the board. By scratching through the 2 pin connection tracks between Q3 and the 14 pins controller IC. (‘Red stars’ in photo board component view).
And connecting those two pins directly to mosfet 50N03’s gate and drain. This way the mosfet still switches on the motor like a good vacuum cleaner did, and its gate current through the on switch is just minimal because of the mosfet gate that draws no current. Mainly since mosfets only switch on gate-voltages compared to transistors that switch on base-currents.
According to the 50N03 datasheet, Vgs allowed is max 20V and has no problem with the only about 8V coming from the 8V battery pack or the 9.6V DC from the charging adapter. And also the max Vds voltage of 30V DC is no problem for the 50N03 mosfet at all either.
Because nothing else was changed and the charging process still worked splendidly before when the motor didn’t work, both battery charging and battery full are again still correctly shown by the dual led. Which blinks red when the charging is active and constantly green when the 18650 cell pack is fully charged. The only downside of this modification may be that the charging adapter probably no longer is protected from drawing too much current when also the motor is running. Although it worked without any issues now when tested, it probably is better to be safe and only use the adapter for charging the lithium 18650 pack when the motor is not switched on. The max current the 9.6V adapter can give is after all only 300mA! Which may be an issue when the battery is fully drained and the motor is switched on!
Of course also the charging of the battery pack was measured and it correctly stopped when the voltage reached 8,01V. Which is completely safe within the maximum of two times the 4.2V DC value. And because I didn’t change anything else on the boards controller circuit or the battery pack, this was a safe and successful repair.
Like often a repair that didn’t cost anything other than a lot of time examining and desolder, test, and resolder parts. Afterwards all it took was a simple bypass of the on switch wiring. To directly switch on the 50N03 (power-) mosfet, that in turn takes over the higher current that drives the 7.2V DC motor like it originally did before the motor stopped working.
A dead vacuum cleaner was completely fixed back to an original working vacuum cleaner!
Albert van Bemmelen, Weert, The Netherlands.
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Note: You can read his previous article on Repair of 31 Year Old Samsung Microwave Oven
March 11, 2023 at 10:57 am
Very ingenious as usual! I am amazed to see how you go so deep in each and every circuit and bring out the essence for people like us to learn! Great work indeed! Very laudable! Many thanks for sharing!
March 11, 2023 at 3:29 pm
nice detailed repair information; it is just great. thanks for sharing your experience with us. have a blessed day
Albert van Bemmelen
March 12, 2023 at 11:30 pm
PS: If you click on the photo of the controller board with the 2 red stars in it, zooming-in and scrolling over the entire component side layout is easily possible. This gives a more close-up detailed view on the Silvercrest board. Jestine added this nice touch to be able to examine where exactly the two tracks were cut to fix and modify the vacuum cleaner!
March 17, 2023 at 4:02 pm
Good fault tracing....
Probably Gate drive missing??
Albert van Bemmelen
March 18, 2023 at 6:52 pm
Probably it was Yogesh, but hard to tell without complete circuit details. A complete circuit is impossible to draw without info on the 14 pins controller ic used here. With the found solution it was no longer needed.