Case Studies

Seeing a gadget restored to life and full functionality is just so satisfying, and we love to share those moments, and the lessons we've learned in the process. Here are a few examples shared by members of the Restart community.

Summary

Some of us have a fix we're especially proud of, or can think of one which nicely demonstrates a diagnostic principle, or which taught us something new. This is a page of "Famous Fixes" which hopefully will contain an ever growing collection of gems for our shared education and entertainment.

Register on the Restarters Forum and look for the "Today I repaired" in the Repair stories category for many more.

Computers and Home Office

Windows laptop

The laptop owner (a very expert user) told the Restarter the harddrive needed "debugging" - led to blind-alley.

• Ran a harddrive diagnostic tool (ok)
• Mounted the drive (ok).
• Inspected system log (ok).
• Booted on Linux and noticed there was rubbish coming up on screen at boot - suspected a keyboard or touchpad fault - isolated the keyboard fault.

(Contribution by Ten.)

Laptop USB port

Only took over half of it, but although the owner had bought the right part it didn't make getting the old usb port off any easier. As there were two big solder points holding the case to the board, it took in a lot of heat before solder flowed. And then there were four connections at the back that you ideally needed to heat all at the same time. We accidentally ripped some of the traces off the board but still managed to fixed it by some fine wire soldered from the pins to a nearby surface mount resistor. The owner of the laptop thought she could have done it herself, and even when I did it I myself couldn't believe it worked.

(Contribution by Faraz.)

Macbook

Mysterious intermittent trackpad problem in which the trackpad button became more sensitive and then stopped working altogether.

• Plugging in an external mouse, the mouse button was not working either.
• Noticing that the battery icon showed no battery present when a battery was present gave a clue as to the fault.
• Turns out the battery had gassed and was bulging, affecting the trackpad
• After removing the battery (and safely disposing of it), the trackpad button was working fine.

(Contribution by David.)

Laptop with black screen

It was a consumer grade laptop, not too old, but the screen was completely black except for a very faint flicker on powering on or off. However the disk light seemed to indicate that it was trying to boot. So it seemed the back light was working but there was no life in the LCD.

The owner had already done a good job of disassembly and reassembly to look for faults, including reseating the video cable connector on the motherboard, but without success. We repeated that, and I couldn't see anything visibly wrong either. It looked like it was either a faulty screen (a new screen might have fixed it) or a faulty video driver (which would mean a new motherboard) but it was impossible to tell which. The owner was ready to give up and dispose of it.

As a last resort and with little hope of success I suggested we see if we could disassemble the screen. This often means complete disassembly of the laptop in order to remove the screen, but with the removal of 2 screws in the screen bezel and releasing the clips around the edge with a spudger, the bezel came off. Four more screws and we could very carefully angle the LCD forward out of the lid. Very careful examination showed that the video cable at the LCD end was unseated by the tiniest amount at one end even though secured by sticky tape. So we reseated it, reassembled the laptop, and to the owner's huge delight the screen immediately sprang to life!

The most satisfying fixes are when an apparently intractable problem eventually turns out to be something very easily put right.

(Contribution by Philip.)

Home Entertainment

Plasma TV

10p lodged inside a plasma TV

"JONNY - DON'T DO THAT!!" Err, too late. With a satisfying clunk, the 10p piece fell down somewhere inside the plasma TV beneath the SDCard slot where 4 year old Jonny had posted it.

I received a panic email from my sister-in-law. Did I think it would be safe to turn the TV on? Err, on balance, I thought, she might get away with it, but on the other hand it could prove expensive. Best not risk it.

I took the make and model number and after a bit of hunting, I found the service manual online. It appeared that the back would come off with the removal of 30 screws in 6 different sizes, and if need be, another 2 screws to remove the side panel where the SDCard slot was. I emailed her back with the details and suggested that given a cross-head screwdriver, she could probably do it. But have an egg box handy for the screws, and mark each compartment to show which screws it contained.

After dropping Jonny at preschool she took a deep breath and set to work. 45 minutes later, including working out how to take it off the stand and plucking up courage to plug it in again, Wendy was able to report with much satisfaction: mission accomplished!

(Contribution by Philip.)

LCD TV

Bad electrolytic capacitors in a TV which had been found dumped in the street provided a good research opportunity. Great team work, biking off to get spares while Faraz unsoldered the failing components.

(Contribution by Ten.)

Two VHS/DVD players

We don't get too many VHS players these days and the complex and delicate mechanism doesn't inspire confidence in repairability. Likewise we not infrequently have to give up on DVD players. So when two VHS/DVD combos turned up at Leightonstone, one with a dead VHS and the other a dead DVD I wasn't brimming with optimism.

Taking the lid off the first, there was nothing visually wrong. Tentatively and for lack of any better ideas, I tried tuning the cam by hand, taking great care not to get fingermarks or any other contamination on it. (The cam is a finely machined and balanced cylinder with 4 record/playback heads in its circumference. It spins at high speed with the tape wound helically around part of it.)

Initially, it seemed stiff, but it quickly eased up and was very soon spinning completely freely. Inserting a tape, it loaded it and immediately started to play! The whole operation only took around 10 minutes.

The other was a bit more challenging. It rattled when you shook it, and it had a DVD stuck in the drive. The owner was bored of watching it.

The rattle was very easily fixed. On taking the lid off it was apparent that a small child (I presume) had posted 2 or 3 DVDs into the VHS slot! But the DVD drive itself (the type with a tray which slides in and out) refused to eject.

I removed the DVD drive mechanism in order to examine it properly. Often with these there's a peg which prevents the tray from ejecting until the DVD has been unclamped from the drive spindle. Through wear, it can happen that the peg isn't withdrawn before the tray starts to move, jamming both the peg and the tray. Taking a tiny shaving off the peg with a craft knife can cure the problem, as it did in this case!

Two out of two: two very happy customers and one dead chuffed Restarter!

(Contribution by Philip.)

Kitchen and Household Items

Kettle

Mysterious kettle owned by the venue - we did not know the circumstances of the fault.

• Check the fuse (ok).
• Visual inspection (ok).
• Tested for continuity from the mains plug to the base (ok).
• Tested base for resistance and continuity (ok).
• By logical process, the only thing left was the physical contact between the kettle jug and the base - turned out it was not making a solid contact and needed to be remade.

(Contribution by Andrew.)

Dehumidifier

This was my own, little used but worked fine for 2 or 3 years but then stopped working. On switching on, the lights seemed to indicate maybe the water collection tank was full, which it wasn't, and it wouldn't stay on.

• Removed covers, visual inspection showed no signs whatsoever of a problem. Reseated connectors with no effect.
• The water level alarm consisted of a float with a magnet which closed a magnetic reed switch as the float approached the full position. No visible faults, and unable to influence the problem with a second magnet close to the reed switch. Gave up for the time being.
• Determined to have one last go before scrapping it. Followed the reed switch wires through to the logic board and hence to a pin on the microcontroller. Verified with a multimeter that the voltage on the microcontroller pin changed as one would expect on lifting the float.
• Noticed that the silk screen printing on the logic board showed a capacitor which was not fitted.
• Followed the copper traces on the board and found that the capacitor (if fitted) would be wired between another microcontroller pin and ground, with a resistor also connecting the pin to the positive supply.
• Theorised that the microcontroller pin was a reset input. The capacitor (if fitted) would hold the pin in a logic "low" state and hence the microcontroller in a reset state while the capacitor charged, for long enough for the power supplies to stabilise. Without the capacitor, the microcontroller might run with unstable power supply and immediately crash.
• Fitted a capacitor calculated to hold the pin "low" for a few tens of milliseconds.
• Powered the dehumidifier on, and it worked like a dream!

Funnily enough, 2 or 3 years later I had a letter from B&Q. A safety issue had been found with this model of dehumidifier, and would I please bring it back for a full refund. Lucky I'd saved it from the scrap heap - I got my refund and bought a new aluminium ladder with the proceeds!

(Contribution by Philip.)

Shaver with broken catch

It was an electric shaver with a shaving head which wouldn't stay down. As a quick fix the user had taped it down with sellotape and had been using it like that for a considerable time. He took the sellotape off and I examined it closely with a magnifying glass (essential these days as my eyes no longer focus as close as they used to). It appeared that a small piece of plastic comprising the catch had popped out of the slot it was meant to locate it. With a bit of gentle easing I managed to pop it back into its rightful place, at which it functioned perfectly, holding the shaver head down but allowing it to be released for cleaning as designed.

Some problems are very simple, but you need to look closely to figure out exactly what has gone wrong.

(Contribution by Philip.)

CD player not playing CDs

A Bush CD Player

CD players that won't recognise a CD I guess are one of the commonest cases where we have to declare a device end of life. So it was fortunate for Derek, who brought his CD player to our recent Repair Fair in Harpenden, that he didn't get his deviice looked at, we being so busy. As a member of the church I've known slightly for many years, I offered to look at it at home, giving me more time than we would have had on the day.

The symptoms were fairly typical, having come on suddenly. However, it did seem to be able to read the number of tracks on a CD but not to play any of them, except once I did get it to play a CD briefly, probably for less than a minute. I wondered whether the laser assembly was stuck at the zero position, allowing it to read a CD's Table of Contents but not move on through the CD. But applying a lithium battery to the motor driving the rack and pinion which moves the assembly across the CD, it appeared to work perfectly.

Inside a Bush CD player.

Disassembly was hampered slightly by the fact that 4 of the 6 Pozidriv No 2 screws were deeply recessed, and my No 2 driver bit was an interference fit in the holes. But pressing very hard on a No 1 bit to prevent camming out, I succeeded in removing them. But there were 2 more screws under the handle which I didn't immediately see, which held me up just a little longer. It came apart into 2 halves, linked by several cables. No obvious signs of burning or failed electrolytic capacitors, though one (at the very bottom of the photo) looked a bit dodgey. Nevertheless, it tested ok and a replacement made no difference. I removed and tested the other high value electrolytics but they were all fine.

Close inspection of the circuit board revealed nothing untoward (nearly all the components are on the underside). But there was a slight discolouration which you can see near the top right hand corner between 2 metal tabs. Here's a closer view: The tabs hold a heat sink in place over a surface mount device. The heat sink was slightly loose since the tabs barely protrude through the board, and the heat sink paste had debonded.

I removed the heat sink, cleaned off the old paste, noted the part number, then replaced the heat sink with fresh paste, securing the tabs as best I could and with a drop of superglue on each tab to prevent it working loose again. On reassembly, it all worked!

So what was that chip, and how did it cause the fault? The part number was SA9614. The datasheet indicated that its function was to control the current through the laser and to amplify and condition the signal coming back from a photodiode which detects the reflected laser light. Replacements for the chip are available from AliExpress, for just a couple of pounds. I've played a couple of CDs successfully though the sound has broken up for a couple of seconds occasionally. I'll return the player to Derek and offer to order a replacemt chip and fit it if the player still isn't satisfactory.

And the moral of the tale? I'd assumed that CD players refusing to play a CD was probably due to degradation of the laser. The active region works at a high power density, so gradual degradation would be far from unexpected. It's probably not feasible to replace a laser, but any player that appears to use a similar chip to drive the laser and process the optical output, replacement of this chip is something certainly worth considering, particularly if there's any sign of overheating. That said, I suspect some newer devices may have those functions integrated into the laser carriage, making replacement of a similar chip more difficult.

PS: The improvement, if it was real, was only temporary. The replacement chip arrived after a few weeks and I fitted it, but no improvement, in fact the problem seemed to have got worse. My original assessment that it was likely laser degradation was probably correct after all.

(Contribution by Philip.)

Electric urn

The electric urn in the church kitchen had stopped working.

Vicar: It could just be the fuse.

Me: It's not often the fuse. But if it's never been descaled, that needs doing, then we'll see where we are.

I knew it wasn't the fuse because on checking it out I was sure a green light had come on briefly, I think just once. Anyway, fuses don't normally blow for no reason.

So I took the top off (levered it off - not quite like it says in the instructions). Drew off as much water as I could through the tap. No sign of the drain cock that the instructions mentioned. Took the front off (no instructions for that, eventually discovered it needed a sharp fist-blow on the bottom). Voila le drain cock. But blocked with limescale. Ladled as much water out as I could with a jug. Tipped the whole thing up to drain remaining water into a bucket on the floor. Searched and found a mop. Mopped up the water that had missed the bucket. Shovelled out a TON of limescale from the bottom of the reservoir. Added descaling stuff and let it fizz. Drained, rinsed and flushed 3 or 4 times then tasted the water - seemed ok (and I'm still alive).

Reassembled, plugged in, tried switching on - still dead. No sign of a thermal fuse thhat might have blown.

Slightly puzzled, I went home. Thinking about it on the way, I thought there'll be a component in the controller that could very plausibly have failed with the observed symptoms, cheaply and quite easily replaced.

Anyway, I'd put the fuse in my pocket to test at home, JUST to prove the point (I hadn't thought to bring my test meter).

Tested the fuse. Re-tested the fuse. Checked my test meter. Tested the fuse again.

Would you believe? It was the fuse all along!! Moral of the tale? Always take the advice of your spiritual advisor - who knows? He might have had a divine revelation.

I went down the following day, replaced the fuse, PAT tested the urn for good measure and tried it. I left it on until the green light came on solid then drew off a cup of water to make sure it was piping hot. All seems good.

You've heard of Schrödinger's Cat - both dead and alive? Apparently we now have Schrödinger's fuse!

In fact, discussion with other Restarters indicated that occasionally, a fuse can go unreliable if the weld joining the end cap to the fuse wire inside fails. You never know it all.

(Contribution by Philip.)

Christmas Lights

This was a small recovery project that started when one of our volunteers brought in a set of led lights that were not working. His supplier had replaced them but his question was could we fix them to avoid them being just put in the electrical waste?

They were USB powered and checking the current consumption indicated that there was probably a short on the controller board, which correlated with it getting extremely hot. Since the voltage for USB is 5V we assumed that these made use of a WS2812 or similar ‘neopixel’ leds.

To test this we connected them to a Pi Pico microcontroller and tried to drive them via the ‘neopixel’ module which worked, confirming our assumption. We then needed to write a few sequences based on some clips of the working set. This was complimented by some additional sequences that we added from led projects we found on the web. We ended up with around 9 sequences controlled by a push button which included: Comet, Xmas lights, Cylon eye, Chase, Rainbow, and Twinkle.

The original controller was housed in a plastic case that used a button to change the sequence so we fabricated a small daughter board to hold the button and purchased a 3D-printed case to house the microcontroller and button. The cost of all this was around £15 as the microcontroller was around £6.40, the case £7.80 (with postage), and another £1 for the switch and associated bits.

Code for pico is on GitHub [here]