Completely Dead HQ Switching Adapter With Voltage Selector Repair
My brother had tried his HQ selectable voltage 1A output adapter on his Android Tablet. But he noticed that the adapter failed to charge his Tablet. Below this adapter model P.SUP.EU1000 is shown.
And he was glad that this failing adapter had not killed his Tablet in the process just trying to charge it. I was asked to check and find out why the adapter showed no output voltage when measured. Why also the red 3mm led (led Vo + marking on the pcb) was no longer active.
The case was easily opened by removing both special triangle screw (tri-lobular like) heads. And next by unclipping the case from the bottom half at the EU mains plug side, because no other screws were used. Which resembles the way in how many DMM meters and also IR remote control cases are closed and need to be carefully opened.
Immediately after I checked the board on the solder side I noticed the black smd component parallel over normal sized diode SB2100. And because those were completely shorted I started by removing the SK36 smd diode. That indeed was the culprit here! Of course I first had already checked the primary fuse F1 T1A/250V plus all primary Bridge diodes D1 to D4 that all were fine.
And after smd diode SK36 was removed the short over diode SB2100 was gone. And I started to test the adapter. Led led Vo worked and so did the adapter showing exact all selected voltages on the Tablet sized charger output plug. Those plugs can easily be changed by another adapterplug by just unplugging and inserting another one. Those are probably also included with this adapter but left my brother at home. Next photo shows the now removed culprit diode SK36. Made with my recently FW fixed G600 LCD microscope (see one of my previous repairs). Here the links to both diode datasheets: https://datasheetspdf.com/datasheet/SB2100.html
https://www.alldatasheet.com/view.jsp?Searchword=SK36
The shorting SK36 diode was probably used as a special protective 60V DC blocking diode and therefore needs to be replaced by a new diode. Which I ordered at the low cost of a six-pack.
Only the shipping cost were almost as high as the set of 50 new SK36 diodes did cost. I only needed one diode here so 49 diodes are spare new diodes for any future repair.
Above and next photos show the working adapter when set to its minimum 3V voltage, and to its maximum voltage of 12V.
This repair reminded me onto another similar repair that I did in the past that was also about removing a single protection diode. It was an article about a “Bad P6KE150A Transient Voltage Suppressor Diode In HP Power Adapter”. That adapter also worked again after that shorting suppressor diode was removed. Of course that adapter also got a brand new suppressor diode afterwards to make sure it kept working safely.
So this article was about another easily saved adapter and again working as new at almost no cost.
Albert van Bemmelen, Weert, The Netherlands.
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Parasuraman S
November 5, 2022 at 10:02 am
A professional approach and fix! Many thanks for sharing!
Albert van Bemmelen
November 5, 2022 at 2:58 pm
Thanks Parasuraman! After I had received the 50 ordered new SK36 diodes and soldered one SK36 smd diode back over the SB2100 diode (cathode onto cathode, anode onto anode) the adapter worked safely overvoltage protected again.
Tayo
November 5, 2022 at 1:11 pm
Well done Albert. I often fail at rectifying these cheap small power supplies for some reason.
I'll keep my eyes peeled next time.
Albert van Bemmelen
November 9, 2022 at 10:27 pm
I know exactly what you mean Tayo, because normally not all small defect adapters are fixed this easily. Maybe in this case HQ stands for High Quality for a reason?
Waleed Rishmawi
November 5, 2022 at 2:08 pm
that is a 3 amp schottky diode SMD. good job on the repair and thanks for sharing the repair and the information about the blown part. have a blessed day
Albert van Bemmelen
November 9, 2022 at 10:47 pm
Yes, although it was a 3A smd diode it must have been the max 60V DC protection that destroyed its diode junction somehow. Have a blessed day too Waleed!
Paris Azis
November 5, 2022 at 6:42 pm
Hello Albert, this is a tricky failure indeed. You must get the habit to check the output for a short circuit before even opening the plastic case of the power supply. I have seen many times this type of failure, the most amazing being on computer power adaptor's shorted output cable, at some point within its protection glove, I mean that plastic hanger which holds the cable on the case of the psu. This type of failure with the psu working perfectly good, but in current limit mode, which you don't imagine during troubleshooting, being the tricky part of it, keeps you searching for the "no output" symptom...
Albert van Bemmelen
November 6, 2022 at 12:09 am
I guess you also mean those special Dell (mostly 19VDC) computer power adapters that measure the given current inside the supply with extra resistor(s) for safety reasons. And also check if laptop or its Lithium-ion battery are charging within limits. In this case opening the adapter was easy Paris. And we already knew it failed working. It already shorted the output. Of course the adapter was re-tested again after de shorted diode was replaced by a new SK36 smd diode. It perfectly charged an Android Tablet on its 5V charging port. And all selectable voltages were again within spec. No idea why this safety diode shorted, nor why they chose to included it in this design.
Lloyd Bond
November 6, 2022 at 7:07 am
very good article
Albert van Bemmelen
November 9, 2022 at 10:20 pm
Glad you liked it Lloyd! Sometimes we are lucky and find a quite unusual defect we are immediately able to pinpoint and fix, with unexpected ease.
Charles Karonga
November 7, 2022 at 7:27 am
Greetings Albert
Thank you for sharing your knowledge and how you solved the problem on this power adapter.
You article are always detailed and packed with information and ingredients for that will
benefit us beginners as well as guiding professionals to hit the nail on the head on their repairs.
Keep sharing your knowledge with us.
Albert van Bemmelen
November 9, 2022 at 10:10 pm
Thanks Charles. A new article about a Samsung TV with flickering backlight problems is already finished and about to be published any day now.
Yogesh Panchal
November 8, 2022 at 6:23 pm
Albert,
Diode is Schottky & rated 60 V 3A can be used it in many types of charger adapters.for professionals must have spare components.
Albert van Bemmelen
November 9, 2022 at 3:22 am
I know Yogesh, and have now 49 new spare SK36 diodes left but normally had never seen these been used in small power adapters this way before. It indeed may be a good idea to upgrade other adapters with these 60V blocking diodes. However probably not all adapters are safely upgradable like the HQ adapter in this repair was. Because shorting the SB2100 rectifier diode did here not blow up anything else, not even a fuse and reduced the output voltage to zero which still may be different in other small smsps adapters?