Saturday, January 30, 2016

Modifying a dual USB charger socket

I bought a cheap pass-through socket with 2 USB ports from Pollin. The blue LED is too strong at night so I modified it, see below for the "before" and "after" pictures. Obviously, the unit is photographed with the mains socket missing, that's not how it actually ships.

The charger is rated at 1A and in my experience is able to provide more than that. It's actually one of the few non-dedicated chargers in the house that is able charge the iPad without triggering a warning on the screen.

Since it doesn't come [directly] from China it's likely built to a decent standard.

By the way, the part number was "94-351077", but it's not on stock anymore.

 The output is based on a THX202H SMPS regulator with decent specifications. The datasheet for that IC shows a reference circuit for a 5V/1A supply, which is what I guess they used here.

The underside shows quite a bit of rework happening: it looks like most of the SMD parts were manually soldered and the right-side USB socket as well. Judging by the quality of the soldering job I'm worried there might be a few cold joints and solder blobs waiting to fall and short-circuit the board.

Other than that, the separation between mains voltage (240V) and the low voltage side (5V) seems adequate.

The resistor that seems responsible for setting the LED current is R6 with a marking of 102, thus a value of 1 kilo-ohm.

I just desoldered that and put into its place a 10k resistor instead from my parts box. Probably any value between 4.7k and 47k will achieve similar results.

As you can see from the second picture, even with a 10 times less current the LED is still plenty bright.

Wednesday, January 27, 2016

AEG MC 4455 repair and mod

I bought this unit as broken for what I thought it was a good price, ~10 EUR while the retail price is around 50 EUR. Since I usually buy stuff that's DOA (Dead on Arrival) the fix turns out to be most of the times a cold soldering joint or a blown capacitor.

But first, in case you haven't bought one, here's a

Quick review

I'm surprised that in this day and age manufacturers still produce units without an auxiliary input, such as the one pictured below.

It claims to have 10 Watt output (maximum), infrared remote, can play MP3s from a CD or USB stick and has a radio. Let's review all of that, again:

The 10 Watt audio output is produced by a SJ2038 chip which can provided a maximum of 2x3.5W into 4 ohms at 5 volts with a THD of 10%.

The speakers are 6 ohms which would mean probably around 2x2.8W output at 10% distortion. Probably less than 4W for decent listening.

To be fair, for such a low power the speakers sound decent, much better than all of the cheap Bluetooth portable speakers out there.
The minimum volume is too loud for nighttime listening, as all Amazon reviewers are complaining. Also the blue backlight is annoying at night.

There is audible hum and hiss during quiet sections at all volume levels. I thought I could also hear quantization noise from the DAC, but I'm not such an audiophile.

While playing MP3 the entire disc or stick needs to be scanned which can take almost one minute. That's the case will all cheap system-on-a-chip MP3 players. During songs there is a significant seek and buffering pause. Before and after the seek phase above, the amplifier is disconnected and reconnected, resulting in a loud pop.

I haven't received an IR remote with my unit but I was able to 'create' one on my Galaxy S5 using the MyRemocon app and the Samsung LX-6000 preset. There's a lot of functionality that's only accessible using the remote control.

The radio has decent reception but is slow to scan and has again an audible pop while switching between stations.

Conclusion: there are much better units out there, probably for even less money. It does look nice though. Save your money and buy something else.


My unit came with the CD drive not functional, missing remote and it also would not read USB sticks. The USB port was as well not receiving any power.

Left side is the front panel with LCD, on the right is the main PCB, power supply at the bottom, amplifier at the top, not visible because of the MP3 decoder and CD driver carrier board sitting on top of it.

Notice the white 2-pin large connector in the middle-left part of the main board - it's the regulated power output for the entire unit, providing 5V. In a comical twist, the red wire is the ground while the black one is positive. You can see the carrier connector (center and above) has the correct labels.

Since I don't want to mess with 220V the first thing to do is to solder some wires that provide a safe 5V supply. Green is positive and blue is negative for the extra thrill of mismatching the polarity:

Tuesday, January 26, 2016

Inside stuff - Lenovo Miix 3 830 tablet

A few months ago I bought a cheap Windows 10 tablet for having a dedicated bench instrument that I could connect the oscilloscope, multimeter, logic analyzer to.
You can see a bit of it in action in the last photo belonging to this post:

Quick review

The bad

This is by no means a powerhorse. It is faster than a Pentium 3 desktop but struggles with Chrome tabs. 2GB of RAM does not help a lot either.

Touch input is a bit spotty, sometimes taking one second to respond to a scroll request. On top of that, Windows 10 is not (yet) optimized for touch input which means a lot of the times you'll be hitting the wrong button or link.

The other annoying thing is that it cannot charge and use its USB port at the same time - I've already tried a few USB OTG hubs with different settings.

Coming out of standby takes between 2 and 5 seconds.

The screen is pretty glossy, but at least it's bright enough to use in daylight. However it lacks a luminance sensor.

YouTube and general HTML5 performance requires a lot of patience. I would suggest disabling autoplay through Magic Actions. Streaming through ChromeCast is choppy.

The speakers sound tinny and are no match for the iPad Air ones.

The good

Enough with the negative stuff, there are actually some pretty nice features.
It runs most software you would generally need in the lab: data logging, spreadsheet/document editing, compiling source code, interfacing various USB development boards. You could connect it to an OBD interface and have a portable car [tuning] computer.

The onboard HD graphics are decent enough to run previous-gen games, LFS runs at a steady 60fps, old-school games (Diablo 2) present no issue.

Using IE/Edge browser is a provides better experience, if you don't care about ads.
Regarding ads, using Chrome with AdBlock plus is a joy and you can finally watch YouTube without unskippable ads. That was the main reason I quit using my iPad Air.

While streaming through ChromeCast / EZCast is slow, using it as a second monitor through SpaceDesk is almost enjoyable.

Battery life is pretty decent, between 3 and 6 hours, possibly even more if doing light stuff.

This will be my main tablet for a while, until the Core M or X8500 units with keyboard covers reach a decent price.

The teardown

Since this part will have a lot of pictures I have to insert a page break here. ---

3D printing a key

The apartment I'm renting is missing a key for the living room so I thought a nice experiment would be to try to print one of PLA. I already saw a talk at 32C3 that PLA has sufficient strength to actuate a lock without breaking.

I took a photo of the lock and did some basic processing (in MS Paint) to make it easier for the website to parse it:

I currently cannot get the website to work again but here is the key that was generated from the keyhole shot above:

After a miniature print I realized it needed a 2x scaling. Some dremel work a bit later:

The underside of the key was removed to make a 'tongue' that is able to catch the latch. Even though the print was done with 80% infill it still broke at the second twist, without ever opening the lock.

The next tenant might be surprised to find a piece of PLA as I was surprised to find 5 1-cent coins inside:

I already had a similar looking key, but with a mirrored pattern. Some more dremel work later I got a functioning key:

The protruding part on the lower right was cut and the upper left side was trimmed a bit.

Time it took to preprocess, print, reprint, postprocess the PLA key: >2 hours
Time it took to modify the lock: 10 minutes