Monday, March 26, 2012

Hitachi 26AX10BC chassis M1CLUX-H TV vertical foldover fix

This is a Hitachi CRT TV from 1995, model 26AX10BC with chassis M1CLUX-H. When first turned on, the top of the image is vertically stretched, upside down, and overlapping at the top of the screen. This means the vertical retrace does not finish before it's time to start displaying the next field. It's called vertical foldover. Here's a picture. (Sorry, it's just a blue screen, so you can't see how the overlapping part is upside down.)
After a few minutes, the problem area starts shrinking, and after about 10 minutes it's gone. However, it always comes back if the TV has been off for a while. This makes it seem like the problem goes away when some component warms up.

It's an easy fix. However, note that the internals can retain dangerous voltages even when the TV is off. They could maybe even kill you. Make sure you understand what you're getting yourself into. Read about the risks and how to stay safe, intelligently decide whether to do this yourself, and be very careful.

The back is pretty easy to remove. Many screws around the edge connect it to the plastic front, and three screws above the back connector panel connect it to the main board assembly. The TV can stand on just the plastic front, so the back can be removed while it is upright. I kept it near the edge of a workbench. This allowed access to the screw at the bottom, and when the back was removed it allowed access to the bottom of the main board. That position seems precarious, but the TV is not too close to tipping over. Make sure that the table is not close to tipping over. Also, when removing the back, make sure that it does not fall and strike the board at the back of the picture tube neck. If you need a service manual, the 27AX5BX manual will probably suffice.

Here is a the main board. It is on rails, and held to the front plastic with two screws at either side. If you unscrew those, you can slide the board out a bit for better access to the bottom. It's worth doing that, because working on the bottom is much easier then. You could even unplug cables and take the board out, but it's not necessary for access to the vertical deflection circuit.
The vertical deflection chip is attached to the C shaped heat sink that's just above where the red high voltage cable bends first after exiting the flyback transformer. Here is a closeup of the area:
You can easily see the brown ring on the top of C625 (47µF/16V) the closest electrolytic capacitor on the right inside the heat sink. That's electrolyte leakage and the capacitor is bad. Another suspect is C627 (100µF/35V on the schematic, with a 50V capacitor installed) the larger and darker capacitor to the left near the nut and bolt attaching the chip to the heat sink. There is a darker area on the circuit board below, like a puddle.

C627 is the pump-up capacitor for the LA7838 vertical deflection chip, and it is the main suspect. It is part of a charge pump. The chip first connects the capacitor to the power supply to charge it, and then it connects the capacitor in series with the power supply, to provide twice the power supply voltage. This higher voltage is used to quickly move the beam back to the top. A problem with the capacitor will mean less power is available for moving the beam back to the top. This will slow down the move, and the beam won't be able to reach the top before it's time to start displaying the next frame. C625 The small capacitor with the brown ring is a power supply filtering capacitor. It could contribute to the problem if the power supply dips when the vertical deflection chip uses a lot of current.

When I looked under the board, I saw a surprise. The trace between the pump-up capacitor and the chip was missing, and one of the capacitor leads was used to make the connection. This plus the different look of C627 made me wonder if this was a previous repair. Could the pump-up capacitor be good, and could the puddle-like mark on the board be from a failed previous pump-up capacitor?
The Yubright capacitor brand and the nature of the failure made me curious, so I tested the ESR of the pump-up capacitor. Although the capacitor still had most of its capacity, the ESR was ridiculously high, and so the capacitor was obviously bad. There was no need to test the small capacitor, because it was leaking badly. After I removed it, there were drops of electrolyte on it.

After cleaning the board and replacing C625 and C627, the TV worked properly. I chose to not replace more capacitors. Yes, it's probable that some other ones are degraded, but there are very many and it's not worth the effort. The real problem here is that a lot of electrolytic capacitors are located very close to heat sinks. Hitachi even used 85°C capacitors there!

Plex Media Server DTS transcoding fix

Plex Media Server unnecessarily transcodes video when transcoding audio for LG clients which can't play DTS. This increases CPU utilization, and it can cause buffering pauses in video if the CPU isn't fast enough. The issue has been in the Plex forums in this thread and others.

This solves the problem. When "Plex Media Server.exe" runs another executable, the attempt is intercepted, and the command line is changed, as described by enachemc on the Plex forum. The command line change tells the transcoder that the device can accept H.264 video at up high profile, 1080p, and level 4.1.

The interception is done using Detours from Microsoft Research. I chose Detours 2.1 because I had problems with Detours 3.0. The code is compiled from PlexTranscodeDetour.c, creating PlexTranscodeDetour.dll. That DLL needs to be inserted into the "Plex Media Server.exe" process. I recommend insertion via withdll-silent.exe. It supports the same switches as the ordinary Detours withdll.exe, but doesn't open a console window. For example, if Plex Media Server is installed in "C:\Program Files\Plex\Plex Media Server" and these files are in "C:\Program Files\Plex\PlexTranscodeDetour", then you can change the Plex Media Server shortcut target to:
"C:\Program Files\Plex\PlexTranscodeDetour\withdll-silent.exe" "/d:C:\Program Files\Plex\PlexTranscodeDetour\PlexTranscodeDetour.dll" "C:\Program Files\Plex\Plex Media Server\Plex Media Server.exe"

I am also including an unmodified withdll.exe, which produces diagnostic output to the console. You only need to try that if you have problems. Alternatively, you could maybe edit "Plex Media Server.exe" to include the DLL via setdll.exe. I don't know if that works.

I recommend using Microsoft compilers such as Visual C++ from Visual Studio Express 2010. Detours does not come with binaries, and if you want to compile it, you must use a Microsoft compiler. You can't even statically link with detours.lib from the GNU toolchain because the linker cannot resolve some of the symbols in detours.lib. If you want to use the GNU toolchain, you can use the instructions I posted earlier to create a detours.dll that you can use. I felt forced to use Visual Studio Express because I didn't think I was allowed to distribute the detours.dll that I created using those instructions.

You can download PlexTranscodeDetour from Dropbox. You are free to do whatever you want with my code here. Detours components are distributed according to the license from Microsoft Research. This code and program comes with absolutely no warranty. Use at your own risk.

Monday, March 12, 2012

Honda keys suck

The battery contacts are covered with grease which results in a bad connection. What at first seems like bad buttons on the module or a low battery is more likely that problem. The positive connection is made by the two contacts at the top of the right half touching the gold pad at the top of the left half. The negative connection uses four contacts in the centre of the left half which touch the battery. All of these are covered by the grease. You can easily see the four grease spots on the battery, and if you look at the full resolution photo, you'll also be able to see grease on the other contacts.

Unfortunately, to fix the problem you need to unscrew the small screw which holds the key halves together. The threads are coated with blue thread locking fluid. If that's Loctite, it's supposed to be possible to disassemble using normal tools. Unfortunately it's not very easy. You need a good screwdriver that fits well, a lot of downward force to prevent slipping, and strong turning force. Heating the screw with a soldering iron might help, and if done carefully, it doesn't seem to damage the plastic. I first got the screw to turn a bit, but it wouldn't go any further. What finally helped was spinning the screw back and forth a bit continuously while unscrewing.

This is a ridiculous design. Changing a battery shouldn't be that difficult. This deserves a recall.

If you want more information on the procedure, here's another guide. The only other tricky thing I encountered was separating the two key halves at the key ring end. They refused to simply pop apart, but wiggling from side to side (ie. rotation around the axis through the key ring hole) allowed the halves to separate. The battery is a CR1616. Some parts of the photo are blacked out because I don't know if any of those numbers are codes for remote unlock or the immobilizer.