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Why Modern Equipment Not Always Can Be Repaired….”?
Recently my hairdresser gave me her electric hair clipper that didn’t work anymore. It had a little charger adapter with charge stand that gave 3.5V DC at 1000 mA (3.5VA) that was still perfectly working. But the motor and the charging/battery voltage level indicator LEDs didn’t.
After I opened the clipper by removing 4 screws I looked at a dual layer PCB with code marking CH-330.
It wasn’t easy to comprehend the way in which the circuit was designed at first because the tracks on the pcb used a lot of VIAs.
This required me to draw the complete circuit on paper first by measuring how all tracks on the top side were connected to the bottom board side.
The pcb had one 3.7V 18650 Lithium battery that was okay. And so was the about 6000 rpm motor that was perfectly working when I attached it to the 3V Lithium battery. And all LEDs worked fine when I connected them to the Black and Red wire probes of my 9V DMM (Kathode Black wire, Anode LED Red wire with DMM selector set at DIODE/BEEP). Following circuit was the result:
The active semiconductor components used were a NPN transistor marking D882M (Q1), an 8 sop Holtek microprocessor type HT48R01C (U1), and a dual mosfet 8205A (Q2), and a (probably type KIA series) 431 adjustable precision shunt regulator (V1). And some other semiconductors were two SS14 diodes (D1 and D3), a dual diode with marking 5C or SC (D2), and a glass type diode (VD1), plus of course the three mentioned indicator LEDs. Next photo shows the HT48r01c processor under the 18650 lithium battery. This processor exists also in 10 pins versions but this one is really the 8 pin version of that chip (with lesser I/O pins of course).
And following photo shows the same board side after the lithium cell was removed.
And here follows the other side of the pcb.
The D882 NPN transistor Q1 is visible with the switch SW1 and in the middle the 3 LEDs. And on the left behind Q1 is also Q2 dual mosfet 8205A visible. And although the board didn’t do anything anymore I noticed that the motor was spinning at perfect speed only after I connected Drain and Source of Q2 together.
This fact could only mean that the HT48R01C processor probably is dead. Could be caused by a chip defect or simply because it had lost its internal firmware? That would mean that I won’t be able to fix it because the processor not only operates the device but also safely charges and discharges the battery. (Like overvoltage also discharging a lithium below about 3.2V is dangerous because the current keeps on rising while destroying the lithium cell internally. And fires or explosions are something we want to avoid at all times! Which is also the reason why some cheap self made lithium operated soldering irons based on short circuiting the lithium battery are very dangerous! And overheating these cells is very dangerous anyway too).
And it doesn’t seem likely that the manufacturer of this electronic hair clipper is willing to share his firmware with the world. It is a bit strange though that this device already carries 3 different names being: E-TEK, ORBIT and PROXELLI.
Anyway to make sure that the device is beyond repair, I ordered a couple of 8205A dual mosfets and also some 431 smd parts. Replacing them is always easier than testing them in-circuit. And to be sure the old components are okay they need to be unsoldered anyway. It most likely proves that the microprocessor is the reason why this device is dead. Maybe other single chip 8 pin charger controllers can be used to fix this device. That is another thing I hope to find out. For now I have to wait another three weeks before my components arrive.
This article does show that a lot of devices simply do not work without (hidden/manufacturer protected) Firmware anymore. And because of it are difficult to repair. Especially in this example were no other obvious reasons for failure are detected. And the real danger begins when all our
devices are connected over wireless internet and are controlled and/or reprogrammed/flashed over wireless internet by others. Or controller chips that simply loose their firmware. (not something that is unthinkable in case of programmed FPGAs that loose their FW… say in about 20 years or more. And they likely also use them in airplanes etc.). In future it could make your car go in another direction or worse. And programming those chips is maybe done by someone that took those secrets with him some 25 years ago?
It gets more complex by the day. There are programming protocols we use when we flash chips. Why we need programmer hardware. And we also need special digital logic analyzers when we want to examine these communication protocols (there are at least 120 different protocols already!) like I2C, UART/RS232, CAN etc.
Even though the simple mentioned microcontroller in this article hardly uses any communication protocol in this device, it still means that it needed a programming protocol and a special (Holtek dedicated) programmer device to program it.
In case we do want to check the communication that internally takes place in all kinds of devices this is very easily possible. There are very cheap logic analyzers we can buy on Aliexpress or eBay that make our lifes so much easier after we have used it a couple of times to check or debug our devices.
With for instance a very cheap affordable Chinese origin Logic Analyzer – the Saleae 24M 8 channel L.A. we can view, check and debug all different port communication protocols.
And even great software can be obtained free at this download site: https://sigrok.org/wiki/Downloads
This very cheap clone Logic Analyzer works perfectly with PulseView from the sigrok site where also all the supported (clone) logic analyzers are shown. See also this very interesting video that explains in a extremely nice way what you can do with such a device and the Pulseview software:
 Sigrok and Logic Analyzers – YouTube
Introduction and experiments with low-cost logic analysers and the sigrok software suite.
And their download site:
Releases. You can download the latest released tarballs of the following subprojects from the sigrok.org download directory.
This PulseView analyzer program shows and recognizes many protocols and is completely free and daily grows by the number of new add-ons. It is almost unbelievable how much time (years!) was spend in creating this fantastic program that now shows its professional capabillities and still expanding protocol decoder.
This Saleae clone logic analyzer can also work as an USBee AX Pro analyzer by selecting with only software: https://gronlier.fr/blog/2014/07/usbee-ax-pro-reprogramming/
USBee AX Pro reprogramming – Bits and Bytes – gronlier.fr
About a MCU123 USBee AX Pro clone on dx.com which is very similar to a Saleae Logic. To use it with the Saleae software, the VID/PID need to be reprogrammed. The …..(more online)
Anyway I hope to have more answers concerning the hair clipper in three weeks time. If the hair clipper still doesn’t work at that time, this article explains exactly why it didn’t and more.
I am confident that all Blog readers and surely students of Noahtech will no doubt appreciate knowing about these logic digital analyzers and how easy it is using such a usefull device. And also how easy it is to own one. Hereby I also wish to thank the writer(s) of PulseView and the Protocol writers of Sigrok and the Sigrok site for their incredible work. I can’t wait to test my logic analyzers with PulseView on my electronic devices.
I hope reading this article was a pleasant experience.
Albert van Bemmelen, Weert, The Netherlands.
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Note: You can read his previous repair article in the below link: