Monthly Archives: January 2019

Windows 10 Boot Problems: error 0xc000000e

Monday morning. Arrive at the office with lots to do. Switch on the computer, and…


That’s not what I wanted to see. There’s lots of advice out there on the web about fixing this problem, but it turned out not to be so straightforward.

The first step was to get hold of a bootable Windows 10 installer. That entailed installing a desktop and web browser on my office Debian Linux machine which normally runs withou a monitor. Downloading the image from Microsoft was easy enough, though it’s 4.5GB in size so takes a while. I wrote it to a USB stick (which I had to go and buy, of course) and…nothing. It turns out that the Windows 10 .iso image is only suitable for writing to a DVD, and is not a ‘hybrid’ image which can work also on a USB stick. Of course, I didn’t have any blank DVDs lying around, did I?

Luckily Linux was able to mount the .iso image so I could see the files inside it. That meant it was possible to reformat the USB stick, creating a single partition formatted FAT32, and copy the files on to it.


This ran in to a problem because the main archive of Windows files, /sources/install.wim, is just over 4GB in size and thus can’t be written to a FAT32 filesystem in its entirety. I tried to fix this by formatting the stick in ExFAT or NTFS, but my PC’s motherboard (an Asus Z77-Wifi) can’t boot from those filesystems so that didn’t get anywhere. I suspect the right answer is to use UEFI boot, creating a FAT32 partition with the EFI folder on it, and a separate NTFS partition with the other files on. But I was in too much of a hurry for that and decided to just put up with a slightly truncated install.wim file.

Now I had a bootable Windows 10 recovery/install USB stick. Great! The advice from Microsoft is to use the ‘fix startup problems’ option available on the menu. So I did that, and it spent a while diagnosing, then proclaimed that it couldn’t fix my PC. Great. I tried the other options (returning to a system restore point, removing the latest updates) but they all denied that my PC had Windows 10 on it at all.

This is getting annoying. Time to break out the command line, which is probably the most useful tool in the Windows 10 recovery toolkit. The official advice from Microsoft is to do this:

bootrec /scanos
bootrec /rebuildbcd
bootrec /fixmbr
bootrec /fixboot

But the /rebuildbcd stage failed for me, with a ‘The requested system device cannot be found’ error. The next advice I found was to manually reconstruct the BCD (the Boot Configuration Data, which tells the boot process where to find the operating system) by doing:

bcdboot c:\windows

But that didn’t work either.


I had to dig deeper. Luckily I’m not the only person to have had this problem. This page at explained more advanced use of bcdboot, in which it’s possible to tell the tool where the Windows installation lives, and where the System partition which holds the boot information is. I had to rummage round with diskpart to find the right drive letters, because the layout of the partitions on my drive meant that they were not the same as during normal operation. However, I came up with the following:

bcdboot e:\windows /l en-gb /s g: /f all

which worked! It completed successfully! Reboot and…the error was still there. Looking more deeply with diskpart, it turned out that the 100MB partition (drive G:) that was supposed to be the startup partition was formatted NTFS and wasn’t marked as active. The screwloose page indicates that the startup partition needs to be formatted as FAT32 and marked as active. Clearly, formatting it FAT32 deleted all the data on it, so I ran the bcdboot command again to re-create it.

Success! After a shutdown, the PC booted and came up as if nothing had happened. I’m happy that it’s working again, but it’s still a mystery how the error occurred. Something must have got corrupted, but I can’t believe that the entire contents of the startup partition got erased and replaced with an NTFS filesystem.



Sony WM-D6C Walkman Pro DC-DC converter repair

This story starts with the long drive from Cambridge, UK to Warsaw, Poland. I like to be able to listen to music to while away the hours in the car, and I decided to use cassettes. Why? Our car radio is faulty, so much of the time there’s hardly anything to listen to. It has a CD player, but almost all of my CDs are stored away, having long since been converted to MP3s. There’s a handy AUX IN jack, so I can plug in my smartphone. But there’s simply no way to operate a smartphone without looking at it, and I’m not taking my eyes off the road at Autobahn speed.

My solution? Cassettes! I’ve got lots of them, generally high quality recordings, which I’ve never digitised, so they’re not stored away. They’re easy to operate with one hand without looking at them, too. But the car has no cassette player. Sorry, had no cassette player. A little judicious eBay shopping got me a Sony WM-D6C Walkman Professional in immaculate condition for a somewhat lower-than-average price because it didn’t work.


The WM-D6C is widely acknowledged to be one of the finest portable cassette machines ever made. It’s pocket-sized, if you have large pockets, and has sound quality and features that rival full-sized hi-fi cassette decks. It can also record, which is extremely unusual for a Walkman-format machine.

This particular example is a very late one. It doesn’t have the posh amorphous head of the original models, but the electronics are mostly easy-to-access surface-mount components rather than the gruesome bird’s nest of wire-ended parts that the early models had. I remember servicing an early one for a student radio station and it wasn’t a lot of fun. I think this one must have expired quite early in its life and been left on a shelf, because there’s no perceptible head wear and the casing is unmarked.

Putting batteries in and pressing play resulted in the ‘BATT’ LED coming on but absolutely nothing else. No clicks in the headphones, no motor whirring, nothing. Fortunately the service manual is readily available on line. ‘Supplement 4’, dated 2001, accurately describes my example.

Browsing the circuit diagram revealed one of the secrets of the WM-D6C’s excellent performance. Most Walkman-type cassette machines used a pair of ‘AA’ cells, so all the electronics had to run from just 3 volts. That’s common enough in 2018, but back in the day it was a real challenge, so the capabilities of the motor and electronics were compromised. The WM-D6C not only runs from four ‘AA’ cells, for a 6 volt supply, but does even better. Almost the first thing it does is step up that supply to about 11 volts. That rail then runs nearly everything, including the motor and audio circuits. A nice generous supply voltage is a good start for getting top performance, especially with 1980s-era technology.

A quick prod with the multimeter revealed the problem. This boosted supply was entirely absent. Seeing as how it powers most of the machine, that would explain the lack of results. The supply rail comes from a much-feared component, the DC-DC converter (CP304). Inscrutable in its little screening can, labelled ‘SONY’ on the right hand side of the picture of the Walkman’s entrails below, it’s often considered unrepairable.


The service manual includes a somewhat misleading diagram of its innards. I think the diagram is actually back-to-front, showing the output and input swapped, because that’s the only way it makes sense. The NPN transistor makes a boost converter in a variation on the classic ‘joule thief‘ circuit, and the PNP one with works with the zener diode to regulate the output by depriving the switching transistor of bias if the output voltage rises too high.

WM-D6C DC-DC converter

The converter wasn’t too hard to remove and dismantle, given reasonable desoldering tools and a powerful iron to unsolder the can. Here’s what’s inside. There are components on both sides of the board, and a certain amount of grey silicone which is easy enough to peel off. Back in the 1980s this would have seemed intimidating in its compactness, but it’s easy to work on given modern tools.

Finding the fault was a case of looking for the ‘usual suspects’: there were two tantalum bead capacitors sitting there looking guilty.  The one on the input was short-circuit, which had killed off the 22uH inductor connected to pin 3, the large green component on the right.

I replaced the faulty components, using a higher-voltage-rated tantalum and a ceramic chip in parallel to replace the capacitor, and a surface-mount inductor with bits of wire soldered on to it. The values aren’t very critical and I just used what happened to be lying around. A quick test, giving it 6V from a bench power supply, revealed a healthy 11V or so at the output.

After reinstalling the converter and reassembling the machine (watch out for the little ‘speed tune on/off’ knob at the back) it worked! It shows signs of having had attention from the phantom twiddler. The head azimuth adjustment screw was tightened up, but good quality sound returned when it was properly adjusted. The peak level meter seems rather unenthusiastic so may need adjustment, and I haven’t checked the recording bias yet. There’s also a forest of little surface-mount electrolytics waiting to dribble corrosive ooze all over the PCB, but that’s a job for the long winter evenings. For now, it’s working. Being able to play cassettes has turned out to be unexpectedly useful. We rediscovered a tape of nursery rhymes from Domowe przedszkole, a classic Polish children’s TV programme, which granted us peace on a long trip recently!