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PSU faults



Also see Unit not working on the Faults and repairs / Initial checks page.

If the PSU is working, you should see a light on the PSU case. If there is no light, check the PSU is plugged into a mains socket,the socket is switched on. If the mains plug has a fuse in it, check the fuse. If necessary, prove the mains socket is working by plugging in something else to try.


If you suspect a PSU is faulty, the simplest way to test it is to swap it over with another one if you have more than one amBX unit. Another way, if you have a multimeter, is to measure the voltage at the PSU plug. This should be approximately 18.5v DC. The correct voltage at the plug is no guarantee that the PSU will perform correctly when connected to the wallwasher and is supplying current, but at least it proves that there’s voltage there. If you want to check the voltage under normal (load) conditions, see the Wallwasher main unit / Wallwasher circuit diagram page for suitable locations to test.


One common fault with any PSU is that the wires inside the cable tend to break due to movement (the same thing is common with headphone wires etc.). This is especially so if the cable gets a lot of movement. Whilst the break could be anywhere in the cable, the most common place is where the flexible cable becomes fixed - at the plug, or where it goes into the PSU.


A light on the PSU proves that it is plugged into the mains supply. In most cases, if the light is on, the PSU is working correctly. If the light is on, but the wallwasher is dead, move the cable gently up and down and from side to side near where it joins the plug. Do the same near where it joins the PSU. Also flex the cable up and down along its length. If the wallwasher lights come on or flicker during this testing, it would appear that there is a break in the wire in the cable. Moving the cable has temporarily connected the broken wire. This will normally mean that the PSU is working OK. The cable will need to be repaired or replaced.



Repair the cable

If the break is somewhere along the cable, then it’s normally a case of cutting the cable either side of the break and joining it together again. If the break is near where the cable joins the plug, the best way is to cut the cable two inches back from the plug and replace the plug. If the break is near where the cable joins the PSU, then the cable will need to be cut about two inches away from the break and reconnected inside the PSU. I’ve not opened up a PSU yet, so I don’t know how easy it is to do so. UNPLUG the PSU from the mains before opening the case. Remember, unplug the PSU from the mains before working on it. Capacitors inside the case could still hold a high voltage, so be careful!



Replacement cable

If you want to replace the whole cable (you will still need to get inside the power supply), Laptopsockets.co.uk advertise one on their site that appears to be OK. I haven’t got one, so I can’t try it. The code is DC66, but nothing is found when that is entered into the search box. One way to find it is to enter JSBP5 into the search box and that will take you to the DC jacks page. In one of the columns, you’ll see the PSU cables. Scroll down until you get near the bottom of the column and you’ll see Sony and others 6.5 x4.4mm with pin... and a list of some of the computers it’s compatible with, beginning with Sony PCG-FX. Click on this and it will bring you to the page with the cable on. The only thing is that the plug is right-angled instead of straight. I’m not sure how well this will fit into the socket, because the wallwasher sockets panel is recessed instead of flush which means that the plug may not go fully in unless it is plugged in sideways. If you aren’t using the audio in socket, or not using the fan socket, then there should be room for the plug to be fully inserted.



Replacement PSU

If you need a replacement PSU, you may find it hard to get one.

The replacement PSU must be at least the same wattage. Rated at 3 Amps, the amBX PSU is approximately 60 watts. It doesn’t matter how powerful the replacement PSU is, as long as it’s a minimum of 60w. 65w and 95w PSUs are fairly common. The voltage is important. The PSU is 18v. There doesn’t appear to be many PSUs that are 18v, and those that are available are usually less than 3A. If you can’t get an 18v PSU, one option would be to get a PSU that has an adjustable voltage that includes 18v in its range. Make sure that it can supply a minimum of 3A / 60w at 18v. These adjustable PSUs are often sold as replacement laptop supplies, but can be expensive. The internet is probably the cheapest source for a PSU, but make sure you get one that’s good quality.


One thing you will almost certainly find with a replacement PSU is that it doesn’t have the right plug fitted. You will have to replace the plug yourself. This can be done by buying the correct plug (see the top of this page), which you will need to solder on, or by using the plug from your old PSU. Cut the wire from your old PSU, leaving plenty of wire with the plug on the end. Cut the plug off the new PSU. Join the plug and wire to the wire on the new PSU with a permanent two-way connector. ENSURE YOU GET THE POLARITY RIGHT!. Test to ensure the polarity is correct before connecting to the wallwasher.


As mentioned, 18v is not a very common voltage. It’s possible that the unit may work on a higher voltage, but it’s not recommended. There is no internal voltage regulation to keep the voltage at 18v. Using a higher voltage, even if it doesn’t damage any other components, could reduce the life of the LEDs if they are being run at a higher voltage than they should be.