Archive for the ‘diy fixit howto’ Category

Casio CFX-9850 serial link to PC.

January 9, 2017

A data-point to place in public domain. This has been explored by others, so there’s nothing novel in this post. The serial RS-232 port has almost disappeared from modern desktop computers. This is a problem if you are looking to connect your Casio 9850 series calculator to your computer. The official FA-122 and FA-123 cables are difficult to source (for a sensible budget), and most (all?) of this series do not have USB.

I have successfully used the Casio FA-124 software, under Windows 7 (64 bit) to communicate with the calculator (CFX-9850G). I used:

  1. An off-the-shelf USB to TTL cable. It must be a 3.3V TTL type, and I’d recommend buying a good quality cable from a reputable seller. The ebay seller usb2ttl is a good place to start.
  2. A bit of 2.54mm single row PCB header. Looks like this.
  3. The Casio SB-62 cable. You may be able to use a 2.5mm stereo extension cable, but the calculator’s shape can make it difficult to use non-Casio cables.
  4. A 2.5mm stereo jack socket (not necessary if you’re cutting up a non-Casio cable).

You only need to make three connections. At the calculator, the tip of the plug is Tx, the ring is Rx and the sleeve is Ground. Connect the Ground to that of the USB to TTL cable, connect calculator Tx to the TTL Rx, and the opposite pair. That’s complete, a set of test leads will work if you’re in a hurry.

Check your computer has not assigned the virtual serial device to something greater than COM9 (if it has, you can change that port number to a single digit). Then the FA-124 software will be able to access it.


I acknowledge that my calculator tinkering is not entirely serious:


Ford Focus Mk2 LED indicators

November 26, 2016

A bit of a technical summary of what you need to do to make them work correctly.

This all started after two things happened in quick succession:

1. Some smart-ass said my indicator was invisible during daylight.

2. An MOT assessor said the paint was peeling off the factory-fit filament lamps, and it may suggest an impending MOT failure next time around. The lamps have to be the correct colour, as well as flash at the correct speed.

The ECU (helpfully … or not) will flash the indicators too quickly if it suspects a lamp has failed. An LED lamp will not pull down the voltage on the indicator supply as much as a filament lamp. This is what the ECU detects, the voltage drop due to the low resistance of the filament lamp. There is no “flash relay” or “flash module” hidden in the vehicle.

To fool the ECU you need to provide some series impedance. The simplest way is to add a low value resistor between the indicator supply and ground. I started with an 8 ohm resistor per side. The resistor is rated at 50W, which is a little over-engineered for something you’ll use intermittently. The simplest way to implement this is in the wiring loom behind the headlamps.

[ If you have changed only the front or rear lamps, one 8 ohm resistor per side is sufficient. If you’ve changed front and rear lamps, you need a 4 ohm resistor per side. You can put two of 8 ohm resistors in parallel to achieve the same thing. ]

Remove the entire headlamp unit, and unplug that 10 way connector. It is a tight fit on to the socket, and there’s a latch to unhook (flat blade screwdriver usually works). The wires are clearly numbered in to the plug. Wire 3 (blue) is the indicator supply, and 6 (black) is ground. Connect the resistance across these wires. I used Scotchlok connectors, cheap and readily available from your local craplins.

Cocoon it in tape, and secure the resistors so they’re not flappin’ in the breeze, re-assemble and test:


The image shows one 8 ohm resistor. I added a second resistor in parallel because I did the LED upgrade rear first, then upgraded the front lamps later.

Backlight replacement of the LG Flatron 194WS monitor.

March 20, 2013

This all started when the backlight would only stay lit for about one second. At first I thought it might be due to a power supply issue. There is previous history on this subject, because there are a few monitors built around the same internal hardware. I followed the instructions there (thank you Corporate Computer) and replaced those six capacitors.

I still had a faulty backlight. For reference, the power board has the following part number EAX35159301/7, and is auto-ranging in its input supply (100-240VAC, 50/60Hz). It has a revision date of 2007-02-26.

So the next thing is the CCFL backlight tubes, so I stripped those out from the panel assembly. The ends showed significant blackening, so perhaps the power supply was responding to an over-current condition on the CCFL by shutting down. Sadly, ebay and google could not find me a cost-effective set of replacement tubes. Also, some six years after the unit was made, LED backlighting has made CCFL backlighting obsolete.

While I had the panel apart, I cut some notches out of the metal surround.

So I went back to ebay and bought one metre of white SMD LED flexible tape. It cost me £1.49, and that included postage to the UK.

The tape was designed so it could be cut every three LEDs, and there are cut marks on the tape. It worked out that I could cut two lengths, each with 24 LEDs. These would fit the top and bottom of the screen, where the CCFL tubes used to be. The tape was 8mm wide, exactly the same as the metal supports for the CCFL tubes. The LED strips require 12VDC, which I could get from the monitor’s own (internal) power supply. If you look where the smaller LCD controller board connects to the power supply, via an 11-way connector, the connections there are clearly labelled.

Having used the adhesive backing on the LED strips to secure them to the metal supports, and lots of compressed air to clean the various light diffuser sheets, reassembly was straight-forward. It was mostly straight-forward. After connecting the LED strips to the power supply, I did a final test before assembling the outer casing.


The result is that the monitor now works, although the backlight is noticeably dimmer than it used to be before it failed. Also, the backlight stays on when the monitor is in stand-by mode. The only way to turn off the backlight is to isolate the monitor at the mains inlet. Given the very small amount of money spent on it, I think these are acceptable compromises.
Something to consider doing is going back to that 11-way connector, and looking if there is a control signal which can be used to drive a simple MOSFET switch, so that the backlight is extinguished when there is no input signal, or when the monitor is in stand-by.

A little note about the batteries for the Philips SHC5100 wireless headphones.

November 22, 2012

The gist of it is don’t rush out and buy the specific part (HB550S).
Buy a pair of regular (Nickel Metal Hydride) AAA size rechargeable cells, try and aim for about the same capacity of 550mAh. Then carefully cut about 3 or 4 mm of the plastic wrap from the negative end of the cell.
Have a look at this image for a guide.
Remember that most of the metal can is the negative electrode, so be careful to prevent accidental short circuits with the extra metal exposed.
If you look in the battery compartment of the headphones, there is an extra metal finger which contacts the battery on the side. This is how the headphones detect if the battery is the rechargeable type.

The Ford Focus Mk2 has a little problem.

November 20, 2011

The problem is that the washer jets (on the bonnet) can allow water to drip down on top of the cylinder head.
This is a quite a common problem.
Eventually water can get inside the sparkplug lead, and allow the spark voltage to leak to earth, causing a misfire.
Having had this problem this week, I would like to share with you what my local garage have done. I think this is quite neat. They have a template to make a simple protective cover like this.
If you inspect your engine (and you should), you probably won’t see the water, as it accumulates underneath that black plastic cover on top of the cylinder head.
You can buy replacement washer jets, official parts from Ford dealers. These have rubber seals, where the original parts don’t.

The quest for the o-ring.

December 10, 2010

I needed a replacement o-ring for my bathroom basin. I tried two of the local plumber’s merchants today, both were very helpful but did not have one of the correct size. Even the world’s on-line tat bazaar, ebay, didn’t have any, unless you wanted a boxed set of all sizes.
I remembered there is a family-run hardware shop, Garner’s. The proprietor had one of the sets of various sizes, and picked out the closest-fitting size for me. Brilliant! The cost was a cheap-as-chips twenty pence sterling and I was on my way.

When tracing a power fault on a laptop…

July 18, 2009

… check the power supply first. 🙂

If, like me, you decide to disassemble the laptop first, it will probably turn out to be a waste of time An educational waste of time perhaps.

Repairing and re-using Allen keys.

June 22, 2009

Although I’m not keen on how easy it is to strip and round-off a small Allen key, I reluctantly accept they are very popular. What I have found is it’s not too difficult to repair a worn key by simply cutting off about 2mm from the worn end.
A worn allen key:

Worn allen key

Worn allen key

After cutting 2mm off the end (Dremel or similar tool):

Repaired allen key

Repaired allen key

Tips: Wear face and hand protection, as the whole allen key will heat up when you cut it with a power tool. After cutting the end will be razor sharp so use glass paper to take the ‘edge’ off.

Easy, takes about 10 minutes including the time to set-up and tidy-up afterwards.