TideLog Archive for the “Work” Category

Today was another tinker day for me, and this time another YouView box from Humax. The T2100 replaced the ageing T1000 which was beset with issues, notably power supply issues with bad capacitors, as well as HDMI handshake problems, and just general reliability and use issues, such as recording failures (attributed to PSU issues, capacitors in the HDD 12v feed rail going dry or high ESR), freezing, and refusal to power on.

Most of the problems were down to the built in PSU which was fully onboard. The latest boxes, the T2100, T2110 and the newer 4K T4000 boxes are much smaller, and now use an external PSU brick, as well as smaller 2.5″ SATA HDD from a laptop, allowing Humax to shrink it massively. I have actually repaired a few in the past, mainly HDD failures due to 24/7 use and the Bathtub curve of HDD reliability being so unpredictable, but it’s the first time on TideLog for me to show you the wonderful neat innards, and much improved electronic design!

The only thing that’s needed is a Philips screwdriver. 4 screws on the bottom (self tappers into plastic, eurgh!) one of them under a warranty sticker (those things are just BEGGING to be peeled off!), remove the machine screw above the SCART socket, and off pops the cover!

I love the inside of these, I just love a neat circuit board, they’re a beautiful work of art in their own right. So, bottom left, the hard drive, which is a standard 2.5″ 500GB AV grade HDD, mine has a Western Digital AV-25 WD50000LUCT, which are designed for CCTV and PVR use, so are fine for 24/7 use. 4 screws underneath it hold it into place, the motherboard has to come out to remove it as it is actually screwed into the mainboard, not the chassis. One nice thing is that Humax have used rubber bumpers with the screws to shield it from knocks (not dropping it down stairs, as some of my repaired ones have been!) and also so that the screws are not in direct contact with the PCB.

To the bottom left of the HDD sits one of the box’s two USB ports, with the other being on the rear under the Ethernet port. To the right of the hard drive is what I assume to be the 12v regulator choke for the HDD, digitally controlled. To the right of that are the 4x1GB Samsung RAM chips, making a total of 4GB, which gives the box its stability power during marathon record 2-programmes-watch-another stints, to save it constantly caching everything to the HDD when rewinding, pausing or fast forwarding live TV, which, when recording two programmes and watching one would cause buffer issues, recordings would be glitched and the HDD under massive load.

Above the RAM is the CPU (possibly an ARM 2 or 4 core, I’ve never looked under the heatsink in one), under the big finned heatsink, which unlike the T1000, does not have a noisy fan cooling it down, it is fully passive, where the heat from it rises naturally out the top vents on the top cover. To the right of the RAM is the digitally controlled, beautifully intricate (shucks, I’m a true nerd!) 3 phase power regulation system. This splits up and regulates the 12v from the external brick, into all the voltages required by the components, and the CPU, which requires an ultra stable, clean and spike free supply. The HDD 12v regulator is fed from this system too.

The Broadcom Ethernet & dual-tuner control chips are to the top of these. This area also contains the white harness connector for the top cover switch block wiring which you can just see in the top of the image above. The switch block in the top cover is nothing special, just a PCB with switches soldered on 😉

There are still a few of the dodgy SamYoung (which brand does that sound like?) Chinese electrolytic capacitors in these units as there were with the old T1000 series. Luckily in the new T21xx series there are only 3 (the T1000 had 10), the rest are solid state, the ones in my unit are fine but we’ll have to see how long it is before they get binned for Japanese RubyCon YXF ones! There are two in the voltage regulation section, and one in the top left of the box below the DC IN switch/plug socket block that will likely be the first electrical repair I do 🙂

There’s not much info on the chips in these, I couldn’t make out the model numbers and a schematic is not in the wild. A future update to this article will be a teardown of the external brick, me using my magnifier (when I find it) to identify the chips and CPU, and exactly where that HDD regulator goes, if it is even for the HDD…

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I had the misfortune of my tablet getting damaged this week. I was working in Rikku’s bus garage, with it resting on the bus’s bumper crossmember taking readings from the ECU, when Rik called me away. While I was away the vibration of the engine caused my tablet to fall off, straight onto tarmac! Luckily the screen hasn’t cracked.

I’ll show you all how to replace the digitizer, as it’s a lot more straightforward than also having to replace the screen, as less disassembly is required.

A. Removing the SD card cover/Wi-Fi antenna

First of all, your digitizer is GLASS, so you can use sellotape across the glass to hold it in place, preventing any injury, or shards of glass falling on the floor. Removing the damaged digitizer will stress it and maybe cause more damage as you do it. The glass provides 90% of the front frame’s strength, so once broken it loses most of its rigidity.

Once you’ve secured the glass, turn your tablet over, and remove the SD cover, which also doubles as a WiFi antenna, by locating the notch on the left, and lifting up. It unsnaps quite loudly, but be gentle. Once removed, place in a safe place:

2-removing-SD-cover

B. Removing the rear casing

Next up we’ll be removing the rear case, which is easy to do as there’s no screws, it’s all clipped together. A lot of the reviewers of the Bush MyTablet reckoned the aluminium back was just cosmetic, but it is actually structural, and gives the tablet weight and strength to prevent flexing of the whole body to protect the internals,.

Using a flat blade jeweller’s screwdriver, unsnap one set of clips between the front digitizer frame and the rear case, and then use a plastic spudger to do the rest. DON’T use a screwdriver permanently, only to get a start. Note in my picture below, the lip of plastic on my rear case near the headphone port was damaged on mine in the impact, so I used this as an easy access point for my spudger:

3-unclipping-digitizer-from-rear-cover-1

Continue all the way round the case, and don’t worry about snapping noises. The screen is clipped to the backside of the digitizer, but as long as you are gentle, it won’t resist too much, and you shouldn’t break anything. The glass may crack and crunch on the broken digitizer at this point, due to the lost strength I mentioned earlier. I didn’t use tape on my glass as I was on a disposable cloth I could just throw away:

4-unclipping-digitizer-from-rear-cover-2

Once you’ve unsnapped all the clips, the rear case will just lift off. There’s nothing attached to it, so just lift it clear, upon doing so you’ll see the wonderous internals of the tablet, including the relatively large battery, and small mainboard. You can also see how the aluminium back actually constitutes most of the rear cover, with the plastic just being a small frame, proving my point about the strength the metal back provides:

5-lifting-off-rear-cover

When you remove the back cover, WATCH out for the power and volume button pack dropping out. It isn’t plastic welded or screwed onto anything, so it’ll just fall free:

6-watch-out-for-volume-and-power-buttons-falling-out

C. Screw and connector locations

Now comes the preparation stage of locating the connectors and screws you’ll need to remove. If you’re just removing the digitizer, there’s 2 screws and 2 ribbons to remove, but if your screen is broken most of the internals have to come apart as the mainboard and battery are mounted to the back of the screen panel’s chassis with tape and glue, both of which are surprisingly strong!

7-screw-and-connector-locations

The ribbon cable connectors for the digitizer and display are under the tape on the left and right sides, respectively, which I’ve labelled in red, the two red circled screws attach the PCB to the digitizer frame. The battery and speaker cables are under the orange tape on the bottom left. These two are soldered in, but don’t need to be de-soldered at all unless you are explicitly replacing them. Even for a screen replacement, desoldering these isn’t necessary, they can just be lifted out the way. To remove the battery for screen replacement, simply break the glue holding it in, and lift it out of the way after the rest of the disassembly is done, leaving the wires soldered in. Don’t do it yet, you’ll end up with a tangle!

The connector flaps for the ribbons need to be flicked upwards NO MORE than 90 degrees VERY gently. If you snap the flap, the whole PCB socket is ruined as the flap provides the torque to hold the ribbon in place, pressing the metal contacts together. Taping it back together is not good enough. DO NOT rush, the same goes for the left one. This is where unskilled amateurs make the jobs more expensive, take it from a professional who has fixed mistakes many times! Modern electronics are VERY delicate, and need eagle eyesight and jeweller’s finesse, shaky hands just won’t do!

From the left, lift the silver tape a little (DON’T damage or discard it as it can be re-used), and remove the ribbon for the power/volume buttons. Lift the flap gently, then ease the cable out.

10-power-and-volume-switch-ribbon-connector-location

From the right, lift the black tape. If you’re going to be replacing ONLY the digitizer, remove just the top ribbon that I’ve circled red, which is the digitizer cable, using the same care as for the power/volume ribbon above. If your screen is cracked, you’ll need to remove the bottom one as well, which is your display cable that carries display signals, and the backlight power.

Again, I can’t stress enough, DO NOT rush, and DO NOT force the socket connector flaps over 90 degrees, if they break you’ve just made the job 80% more expensive as you’ll need the sockets replacing, or a new PCB, which will involve data recovery off your old board, especially if you damage the touchscreen connector!

11-digitizer-ribbon-connector-location

D. Removing bottom frame support

Where the speaker is along the bottom you’ll notice a plastic frame screwed into place. This is like a strengthener and support in one unit, it holds the speaker in place while giving the bottom of the digitizer some strength. It also carries clips that the rear cover was mounted to, so I consider it a main structural member of the whole tablet chassis. Simply remove the two screws, and lift it off the digitizer. Watch out as the speaker is now loose on its cable and will slide around!

8-screws for-frame-support

E. Removing screen & mainboard assembly from digitizer

If you look all around the inside of the frame you’ll see lots of clips holding the screen in place. We’re now going to remove the screen VERY GENTLY. This is another step that you should take your time, there’s no medal for rushing it, as you WILL likely break your screen if you do it wrong, the glass on the screen is thinner than the digitizer. That’s the reason tablets have their digitizer separate to the screen, mounted half an inch away.

If your screen and digitizer are already broken and you’re replacing them both, I personally would still be careful, because I’m a professional, and normally it’s someone else’s equipment, which I respect 🙂

9-clips-attaching-screen-to-digitizer-frame

So, while unclipping the clips (they may be stiff) you can use a spudger to keep the screen from re-clipping itself in, but DON’T overdo it, don’t lever the screen too high with too many clips still securing it, it will flex and break. Obviously if your screen is broken and you’re replacing it this isn’t relevant, but still take care, because I would 🙂

The image below shows me using my spudger as the clips are unclipped, my screen wasn’t damaged before, and it wasn’t damaged after, apart from a scratch on the glass caused by the digitizer imploding on impact!

12-unclipping-screen-clips-while-lifting-screen-GENTLY

Finally, once that’s all done, you can separate the digitizer from the rest of the chassis, and pat yourself on the back for getting this far without any major damage, unless you DID damage something I told you not to, in that case it’s your fault for not listening to a pro, take yourself off to the naughty corner and think about what you’ve done!

Otherwise, if all went well, you’ll end up with the tablet looking like this:

13-chassis-and-digitizer-separated

Re-assembly with a new digitizer is the reverse of removal, if you remember my advice you should have a fully functioning tablet that acts as if nothing happened once it is rebuilt!

F. Extra steps for screen replacement

I only had to replace my digitizer, but if your screen is damaged as well, once you finish with the separated digitizer as step E, you’ll need to:

  1. Remove the display cable connector as I mentioned earlier
  2. Separate the battery from the screen back by removing the glue. When you reassemble the battery onto the new screen, use *new* adhesive strips instead of glue to secure it, as you don’t want it rattling around, its metallic case can short stuff out, which you DEFINITELY don’t want happening.
  3. Remove all the tape strips holding the PCB,
  4. If you’re also replacing the battery, desolder the battery cables, making sure you note the polarity. Resoldering the cables the wrong way may short the board out, and cause an expensive mess. I don’t know if the Chinese electronics in these have decent short-circuit protection, and I’m not willing to find out!
  5. Re-assembly, again, is the reverse of removal. With new parts, TAKE EXTREME CARE, you don’t want your new screen or digitizer damaged again! And make sure all the tape is replaced and secured in the original places. Mark out where the strips sit with a marker pen.

Good luck!

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This is another wear related symptom, and often occurs on power down of an old system after a power cut. It is again to do with the input regulation circuit (the main resistor, diodes, and rectifier transistors bolted to the keypad chassis). If your Optima starts OK on battery, but not on just the mains, the cause of this is the CPU isn’t getting enough power to start up from the AC to DC rectification stage. The start sequence goes visually like this:

  1. Power is applied, the regulators get up to working voltage, and start supplying power to the CPU.
  2. The LED’s all come on, briefly, as the CPU boots up, doing its self test of itself, and the NVRAM, containing your code and exit/entry timers.
  3. Within a few milliseconds of 2 above, once the CPU has started, the LED’s go out, and the alarm now goes into a full alarm condition, leaving just the Power LED on, and any open Zone LED’s. If no zones are open, just the power LED is on.

If the LED’s all stay on with no more activity or sound, the CPU isn’t starting correctly, because the voltage to it is insufficient coming from the AC to DC rectifier stage. Allowing the alarm to start here going into full alarm, would cause too much current inrush, and voltage drop to sustain keeping itself running, due to the strobe/bell and 13v PIR’s drawing power when there isn’t enough.

The transformer puts out 16.2v AC. If the voltage at your battery charge terminals with no battery connected is less than 14v, (the last one I did was 10v) the whole system is being starved of power. The two transistors that are bolted through the keypad chassis need to be replaced, the big three-legged things top right of this picture with the holes through the tags:

Optima-XM-board-faulty-regulators

I always replace both to make sure, as they can be quite stressed out at such an old age, and be breaking down under load, as does the 47 ohm battery resistor. I also check the capacitors accompanying them. The leftmost transistor is a Toshiba TA7805S Positive Voltage Regulator which seems to be the battery regulator, I’ve uploaded the datasheet to Tidelog HERE. The second (rightmost) transistor is an ST Microelectronics LT8I5CV, for which I cannot find a datasheet, and I assume is the AC rectifier stage’s main DC regulator.

I am attempting to find suitable modern equivalents for these regulators, so if any electronics guys out there can help, I’d be most grateful, as finding info on these 15+ year old components is tricky! I’m running out of working ones to cannibalize off old unrepairable Optima boards! A good alternative to the Toshiba TA7805S is the Panasonic AN7805F, the datasheet is on TideLog, HERE, for you to take a peek at, if you understand electronics 🙂

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Hoover washer dryers used to be synonymous with quality and could go 10 years plus without issues, but now they just seem to be dropping dead left right and centre when really young. In the space of one day today I’ve both had a Hoover engineer come out to my parent’s machine, for a motor replacement under Hoover warranty, and later that day I myself was called out to fix another Hoover washer dryer, both the same model, different faults.

WDYN856DG

The patient was a 2 year old WDYN856 DG washer/dryer, with no signs of life, except clicking noises, following a loud bang during a dry cycle. Clicking relays are usually always main control unit failure, so myself and Martin, my repair assistant, got to work. There was no other life from the programme selector dial, LED segment display unit, buttons, or their LED’s, apart from the clicking. We pulled the control unit out, it looked fine from within its casing, but once unclipped from it, we saw the catastrophic damage:

Hoover-WDYN856DG-control-unit-PCB-in-shieldHoover-WDYN856DG-control-unit-PCB

Can you guess where the actual brain of that massive washing machine is? Nope, none of the big components! That tiny chip that I’ve circled in red is the computer of the machine, smaller than a two-pence piece! The rest of the board is just power regulation, the control relays, and the outputs for the motor and element, plus all the connectors for sensors. The two small plugs on the very right-middle are the programming headers for programming the EEPROM. You can see the giant ferrite inductor coil, and those big heatsinks? That’s the transistor & Triac that control the motor speed, they act as an inverter and tacho control. The higher the switching frequency of those transistors, the faster the motor spins. They get mad hot, and very stressed, especially the massive transistor to the right of the coil.

Unfortunately, as you can see from the picture, around where the microcontroller is, that is where the failure has occurred. The area is all burnt, and has catastrophically shorted. The yellow highlight on the left is also where some damage to a diode, resistor and capacitor has occurred. The damage is actually worse than it looks in the picture.

We had to replace the motor, and the front-end option selection button unit as they were unresponsive even with a new control unit. We can’t be sure of the exact cause, but we suspect the motor has shorted, and as it’s directly wired to the transistors, has caused a massive short circuit, taking out the control unit and the option selection button unit (which itself had microcontrollers on it, but these were visually undamaged).

Unfortunately you can’t just buy a new control unit and connect it up, the EEPROM needs to be programmed with machine specific code, the machine will just flash an EEPROM communication error otherwise. We had the Hoover engineer programmer, so were OK 😉

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You’ve all seen them, the bulbs that are supposed to help the environment, with swirly tubes, short and fat, long and thin. Their efficiency comes from the fact that, unlike filament bulbs, the tubes don’t draw their current direct from the mains, instead they use a kind of inverter, known as a “ballast”, very similar to the ones used in laptops for backlights. Except these run on high voltage inputs, unlike a laptop inverter which will run off 9 to 15v DC and provide 1000v AC ignition voltage, with 300 to 800v run voltage depending on brightness setting.

Unlike a laptop, though, fluorescent lamps aren’t variable brightness. The ballast puts very little load on the AC input, instead it itself provides the current to drive the tubes, like a middleman.

Benefits

Compact fluorescent lamps have some benefits in comparison with standard filament light bulbs:

1. Lower power consumption (as much as 80%) and

2. Much longer life expectancy when used in the correct environment with airflow (5 to 15 times)

Disadvantages:

1. Longer warm up times (mainly only experienced with cheaper bulbs)

2. Cannot be run off a dimmer switch.

3. Cheaper bulbs tend to be failure prone under heavier use more than 3 hours per day, or if not provided with adequate cooling around it.

4. More expensive per bulb than a filament one, but cost savings are made over its life to offset initial cost.

5. Depending on the colour temperature of the bulb, lower colour temps are not suitable for use as backlighting when using a camera.

Available colour temperatures

Fluorescent lamps are available usually in these color temperatures:

  • Warm white (2700K)
  • Cool white (4000K)
  • Daylight (6000K)

The most common colour temperature is “warm white”, which is close in brightness to a classic 60W filament bulb and also is most pleasant to people, but cannot be used as ambient light for use with a camera.

Principle of construction and operation

Compact fluorescent lamps use a vacuum tube similar to classic strip lamp, the principle of energy transformation to visible light is the same. On either end of the tube are two electrodes coated with Barium, the tube is filled with Argon and Mercury. The cathode runs at high temperature (about 900 degrees Celsius) and generates many electrons which are accelerated by voltage, bouncing between electrodes, hitting the atoms of Argon and Mercury. This gives rise to low temperature plasm. The mercury energy radiates in a UV light form. The inside of the tube is coated with luminophore (phosphor), which transform UV light in to the visible light that you see.

The tube is powered by alternating current, provided by the ballast, so the electrodes (cathode and anode) switch on and off, alternating rapidly. Because of the use of a switched converter in the ballast, which runs on tens of kilohertz, the CFL lamp doesn’t flicker in comparison to a classic strip tube lamp. The converter, which is present in the screw or bayonet cap, substitutes the starter found in traditional classic strip lamps (which are wired direct to AC line), making CFL’s more efficient.

Here’s a look inside a Philips Genie 11W, for the curious electronic nerds out there 🙂

Philips Genie 11W

To help understand that little circuit board a little more, here’s its schematic diagram:

philipsgenie11w-schematic

 

Theory of Ballast operation

The lamp requires a current to preheat the filaments, a high-voltage for ignition, and a high-frequency AC current during running. To fulfill these requirements, the electronic ballast circuit first performs a low-frequency AC-to-DC conversion at the input, followed by a high-frequency DC-to-AC conversion at the output.

The AC mains voltage is full-wave rectified and then peak-charges a capacitor to produce a smooth DC bus voltage. The DC bus voltage is then converted into a high-frequency, 50% duty-cycle, AC square-wave voltage using a standard half-bridge switching circuit. The high-frequency AC square-wave voltage then drives the resonant tank circuit and becomes filtered to produce a sinusoidal current and voltage at the lamp.

During pre-ignition, the resonant tank is a series-LC circuit with a high Q-factor. After ignition and during running, the tank is a series-L, parallel-RC circuit, with a Q-factor somewhere between a high and low value, depending on the lamp dimming level.

When the CFL is first turned on, the control IC sweeps the half-bridge frequency from the maximum frequency down towards the resonance frequency of the high-Q ballast output stage. The lamp filaments are preheated as the frequency decreases and the lamp voltage and load current increase. The frequency keeps decreasing until the lamp voltage exceeds the lamp ignition voltage threshold (up to 400v) and the lamp ignites. Once the lamp ignites, the voltage drops and the lamp current is controlled such that the lamp runs at the desired power and brightness level.

Failures

Common failures are faulty output capacitors, a major fault in cheaper bulbs, where cheaper components are used. When the tube doesn’t light up on time, or fully, there is a risk of destroying the transistors and their resistors. Lamp startup is very stressful on the ballast circuit, transistors usually don’t survive overloading at high temperatures, taking out the transistors fed by them. When the tube fails, the electronics are usually destroyed too. When the tube is old, the filaments become worn, causing high resistance to the circuit and either tube doesn’t lights up anymore. Normally in this case the electronics usually survive because the ballast will shut down if there is a loss of load caused by death of the tube. Sometimes the tube can be wrecked due to internal tension and temperature difference. Most frequently a stressed tube fails, when powered on, making it look like the whole lamp has failed.

Failure of the whole lamp at its worst is normally limited to a little bit of smoke, and/or a bad smell, and a small pinging noise. They are not allowed to “POP!” or cause direct shorts on the AC line, the input fuse on the ballast will prevent that.

Repair of electronics

Repair of the electronics usually means change of capacitors. When the fuse has popped, this signifies possible damaged transistors and resistors. Failures can be multiplied. For example, when there is shorted capacitors there can be thermally overloaded transistors that will be destroyed. The best transistors for replacing of original types are MJE13003, but they are not easy to find recently. I replaced them with BD129, but they are not available now. There exists other variants like 2SC2611, 2SC2482, BD128, BD127, but I am not sure if they will be long-life.

Mechanical construction

A fluorescent lamp is usually comprised of two parts. One is the plastic cover with holes for the tube and vents, and the plastic clips to attach to the bottom section. The tube is glued in using high temperature epoxy or cement glue. The bottom section has slots for the clips from the inner side. Inside is the printed circuit board with components and wires from the tube. From the upper side of the PCB are wires to top of the lamps, which are soldered or stamped to the contacts on the PCB, normally metal posts. Both plastic parts are clicked together and sometimes glued. Usually you can carefully leverage the casing with a small screwdriver sequentially to release the glue. Next you must leverage more to open the lamp. To close the lamp housing after repair you can only click both plastic pieces together.

Sometimes opening these lamps up is harder than the repair as the housing often gets damaged, lamps that have been heated and cooled regularly tends to lead to the plastic becoming brittle and hard to separate!

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