Repairs

Warning!

When checking things out on an accessory, Be careful!. The components on the PCB are close together. The slip of a test prod or a screwdriver could create a short circuit and potentially damage the sidelight or wallwasher. Unless you need the accessory plugged in to test, unplug it from the wallwasher. Remember that the PCBs are double-sided and have components / contacts on both sides. There’s always a chance that you could rest the bottom of the PCB on something that is conductive, like a screw, and this could cause a short circuit if the PCB is live. If using a multimeter, make sure that the leads are in the correct sockets or you could potentially cause a short circuit through the component or equipment that you are testing.

ESD

Many components can be damaged by static electricity (Electro Static Discharge), this includes the LEDs. Remember when you used to rub a balloon up and down your jumper then stuck it on the wall? - that’s static electricity. Likewise the crackle that you get when you take synthetic material out of the tumble drier is the crackle of static sparks (they light up in the dark!). That same static can zap electronic components.

Whilst the PCB has ESD protection, you still need to be careful and take precautions. If you are replacing a component, such as an LED, this will be unprotected until it is soldered into place. Many surfaces can hold static electricity, and this can be transferred to a component if you’re not careful.

Take normal anti-static precautions, such as earthing (grounding) yourself before touching the PCB, components etc. One way to do this is via a special ESD wrist band that is connected to an earth point Another way you can do this is to touch a metal part of the computer that is plugged in (not a laptop, it’s not connected to earth) or connect a USB lead to the computer and touch the metal shell of the USB plug / socket before touching the PCB. If you want to ensure you’re earthed all the time and don’t have the wrist band, one way would be to have the shell of a connected USB cable permanently touching your skin. A crude, but effective way is to tuck it under your watch strap, although it does limit hand movement a bit. Or you could it into your sock, but this might not work so well.

Use your common sense. I must admit that I’ve rarely taken all the correct ESD precautions. Careful preparation and handling can eliminate a lot of the risk. Earth yourself and tools before touching the PCB or component and avoid handling them too much. Remember, many soldering irons can be a cause of static, especially if they’re not earthed. One way to get around this is to clip a crocodile clip onto the soldering iron metal body furthest away from the tip (at the coldest point) and connect an earthed cable to the clip. It’s something I’ve done in the past, but I don’t know how effective it is.

Be practical in your choice of where to work on the accessory. An empty table with plenty of light is ideal. Opening an accessory on a nylon carpet with its static properties is not the best choice of work surface (although it’s something I’ve frequently done!). Likewise wearing a cotton shirt or T shirt etc. is better than a synthetic one as cotton is less likely to attract static.  

Working on the equipment

Always have a pen and paper to hand to make any notes you want.

Most of what you want to do will probably be associated with the sidelight or the wallwasher. Unless it is necessary for the checks, unplug the sidelight. This will help reduce the likelihood of any damage. Only plug the sidelight in when you need to do checks or alterations with the LEDs on. Likewise with the wallwasher. Remove the PSU plug from the wallwasher whenever possible, especially before unplugging the LED PCB connector cable. Remember, even though the PCB or wallwasher may be disconnected, it’s possible that the capacitors could still retain a charge for a while, especially on the VCC line and could still cause damage if shorted against another component. It’s also possible that it might give you a wrong reading if you’re taking measurements. As an example, on a test on the sidelight PCB, when the sidelight was unplugged, VCC dropped very quickly, but remained at around 1v, slowly dropping to 0v.

If you have to work with the LEDs on, unless you need them at full brightness, turn the brightness down via the individual light setting in the DirectControl panel or something similar. The LEDs are deceptively bright and can cause temporary sight problems or discomfort, even if looking at them for just a short while. If I have to look at the LEDs, I use sunglasses. The colours are still distinguishable.

Resistance readings are taken with the equipment disconnects or switched off at the mains. Voltage readings are taken with the equipment connected and switched on as necessary.

Testing the wallwasher sockets

There are times when you may need to measure the voltage at the wallwasher sockets.

One of the simplest ways is by using thin wire, insulated except for about 3 - 5mm at each end. One end is connected to the multimeter probe, the other is pushed into the socket hole. This must be done gently. Do not force the wire into the hole or you could damage the hole. I use the Flexible Jumper Wires which are designed for breadboarding and they are ideal.

The sidelight connection on the wallwasher has pins surrounded by the shell, which makes it difficult to get at the individual pins without shorting across them or the shell. This is easily overcome by connecting a VGA female socket over the pins. This will then give you access to the connections in the shell. An alternative method, is to use an all wires connected 15way F-F extension cable plugged into the wallwasher socket. This will then give you a socket with holes in at the other end of the cable which you can connect the test wires to.

Remember

The fan, rumbler and sidelight sockets need connections shorted together for the accessory or the accessory won’t be detected and you won’t get proper readings. It is important that you short the correct contacts together. Shorting the wrong ones could damage the wallwasher. Details of the socket pin-outs are shown on the relevant accessory page.

Surface Mounted Devices

SMDs are used a lot in electronics these days, partly because they are generally cheaper than standard devices, but more importantly, they’re smaller. The amBX system is no exception. If you’ve never opened the wallwasher or sidelight, then you may not have seen a SMD - they’re small! The scale photograph of some of the components used on the sidelight PCB gives you an idea of what they’re like compared to a 5p piece. The ruler scale is in mm. The font is Arial.

To quote the official specification size:

0805 Resistors and capacitors used on the PCB: 2.0mm long x 1.24mm wide x 0.45mm thick

Transistors and diodes 3.05mm long x 2.5 mm wide x 1.12mm thick

By comparison, the LEDs are quite large at 3.5mm x 2.7mm x 1.9mm

To put this in perspective, the figure 6 in 6 point Arial text is approx. 2.0mm tall x 1.6mm wide

Soldering

Soldering SMD components is more complicated that ordinary components. For one thing, there is no easy way to fix a component to the PCB before soldering - there are no holes to poke wires through. Another thing is the size. SMD components are very small and need to be positioned accurately. Soldering has to be very precise to ensure the component doesn’t move before the solder sets, and you have to make sure the soldering iron bit doesn’t move the component as you are soldering. One other problem is heat. Ordinary components are fairly large by comparison and can absorb more heat than a tiny SMD component can before damage occurs. LEDs, the component you are probably most likely to be changing, are easily damaged if the heat is applied for more than a second or two.

If you’ve never done any SMD work before, practice before actually working on the amBX equipment. Most electronic products have SMDs in them these days and you must have something that’s mot working that you keep meaning to throw away!. Practice desoldering and soldering the components. Remember, that too much heat will probably damage a component, especially LEDs, so you need to solder as quick as possible. Have a look on YouTube for videos on SMD desoldering and soldering.

Tools

Having the right equipment is essential when carrying out SMD work. Whilst you could possibly scrape through using tools that you use for ordinary electronics work, it is much easier when you have the right equipment. The problem is that some of the tools that you should really use are expensive. This doesn’t really matter if you are likely to use them a lot, but if you only want to replace a LED, then buying the tools just for one repair would make that repair very costly, although some tools, like tweezers and a magnifying glass may come in useful when doing other work. Some information on the types of tools that will be a help is given below.

Residual Current Device (RCD)

AN RCD quickly switches off the electricity if there is a fault and can protect against electrocution. If you are working on mains equipment where the mains is switched on and there is the risk of contact with any mains connection, use an RCD for your own protection. Some household supplies may already have RCD protection in the consumer unit, but it may not cover all circuits. Be safe - if you haven’t got one, buy a portable RCD, they are cheap. They plug into the mains socket and the equipment plugs into the RCD.

Always use an RCD if you have to open up the subwoofer box.

Screwdrivers

Depending on what you want to do, at the very least you will need a screwdriver. Most of the screws in the amBX system can be removed using a Philips no.2 size screwdriver. A no.2 size pozi screwdriver may work, but the Philips one will usually give a better grip. A smaller size may be required for tiny screws.

For places where access is restricted, such when removing the amplifier PCB, a “stubby” (short) screwdriver is ideal.

Soldering iron

Whilst it’s possible you could get away with using an ordinary soldering iron, a “SMD soldering tweezers” soldering iron is much better. This has two solder bits and they are held in the same way as tweezers to apply the heat to melt the solder on both edges of the component. They are also useful when desoldering a component. Get some good quality thin core solder. It’s no good trying to solder a tiny component with a big blob of solder!

Desolder tool and desoldering braid

Although it may be difficult to use a desoldering tool on SMD components, the PCBs and other equipment still have some through-hole connections for the larger components, such as electrolytic capacitors or pots. Or, as in the case of the rumbler, soldered connections to the motor. Desoldering braid can be used on SMD components (beware of heat damage)  or on the PCB to clean up the remaining solder. Get desoldering braid of different widths. You normally only need narrow braid for SMD work.

Solder

One of the difficulties these days is that newer electronics use lead-free solder. This can be a lot harder to work with and cause problems if you’re not used to it. Do a Google search for lead-free solder to find out more information. Lead free and the old style 60/40 tin/lead solder don’t mix together very well and may cause joint problems. You should always use the same type of solder when resoldering a component, or make sure that you remove all the old solder from the component and PCB first. Personally, I prefer the 60/40 solder which was much easier to use. This was fine for occasional work as long as you made sure you had good ventilation where you were working and didn’t breathe in the fumes. 60/40 solder is still available, although you may find that local electronics stores such as Maplin mo longer stock it. Rapid electronics still sell it.

Tweezers

Decent tweezers are essential. Remember, the tweezers will be gripping something that is tiny. You don’t want to use cheap tweezers that don’t meet properly. Likewise, you want to have something with a decent grip on them. Imagine trying to look for something as small as a dried chili seed that has popped out of the tweezers’ grip and fallen on the floor!. A pair of ESD coated tweezers are best. These will give protection against ESD damage when handling the components.

Magnifying glass

You will need a magnifying glass, ideally two types, depending on what you want to do.  For close up work, when examining the PCB or components, then you need a powerful one. You could use a handheld one, but a hands-free one is best. I personally like the “Double Magnifying Glass for Spectacles” which clips on to a spectacle frame. This has two lenses of different magnification and you can move one or both over your eye to look through them. Even if you don’t wear glasses, or if you do, but don’t want to clip the magnifying glass on to it, just get a cheap pair of reading glasses from the £ shop to clip the magnifying glass on to. Another option is a loupe (jeweller’s eyeglass) which comes in different magnification strengths.

For working on the PCB, you definitely need a hands-free magnifying glass as your hands will be full with the soldering iron etc. There are various types around. I have two that I use that clip onto a table or bench. The first is a Tchibo make which has a 130mm round frameless lens at the end of a flexible stem which can be bent into any position. The lens has a smaller area of higher magnification. The other magnifying glass is is a largish illuminated one from Maplin, like the sort you see on the TV in path labs etc. This has the advantage that the work surface is illuminated and there are no annoying shadows. There are various types of desk magnifying glass around that you can chose from. Make sure that there is sufficient space below the lens head when it is in position, so that you can work underneath it with a soldering iron etc.

Test the magnifying glass to see if it is suitable before buying it. Take a sample sheet of paper with you with some text printed in normal (not bold) Arial font in font sizes 1, 2, 3, 4, 5, and 6 point. Some of the text on the small components is about the size of 1 point. If you want to be able to read this, you’ll need to make sure the magnifying glass is powerful enough.

Continuity tester

You will need a continuity tester for various checks. There are different ones around, but probably the best way is to buy a cheap digital multimeter. These can be bought for a few pounds and can also be used for testing the voltage at different places. Use the resistance setting. A resistance reading of 000.0 ohms means that the continuity is good. Some multimeters have a continuity setting which will give a continuous tone if the continuity is good. These are better, because you don’t have to keep looking at the meter reading during testing.

Multimeter

A multimeter is essential if you want to check voltages or resistance. It will also work as a continuity tester. Buy a digital meter as this will give you more choice. Generally, you get what you pay for. A cheap one will cover your basic needs and should be reasonably accurate. A more expensive one will have more features. If possible, get one that also has a diode tester. This can be very useful when testing the LEDs.

Multimeter cables / probes

Many probes have a long bare tip. The problem with this is that where the components are close together, the probe can short across nearby connections. This is easily solved by putting a piece of sleeving over the probe so that only the tip is left bare (see photo at the end of this page). If you don’t have any sleeving, you could use insulating tape, but experience has shown that that the tape tends to unravel after a while and it also becomes very sticky.

Whilst the probes that come with a meter may do the job, because of the smallness of the components, some additional probes may be useful. One type are the 4mm SMD probes from Rapid. These have a fine tip which means they can be positioned more accurately and there is less chance of them touching an adjacent pin and causing a short circuit. Another type are the tweezer probes. These are shaped like tweezers, but with individually isolated tips - each tip going to a meter connection. To use, you just line them up either side of the component, at the soldered side, and squeeze the tweezers until the tips make contact with the component’s contacts. This can be done with one hand and is much simpler that trying to line up two separate probes on the contacts. They are ideal for testing LEDs using the diode test. The only problem I found was that there was too much bare contact at the end of the tweezers which, when components are mounted closely together, means there is more risk of shorting the tweezer tip against another component. This should be easily solved by covering most of it up with heat-shrink sleeving.

Oscilloscope

Although not essential, if you have an oscilloscope, this can be used for displaying the voltage and also the waveform of the signal. I have a PoScope which plugs into the USB port of the PC and uses the monitor for the display. Whilst it is cheap, and basic, it’s suitable for what I want to use it for. One advantage is that it can display two separate inputs on the screen, allowing me to monitor two separate things at the same time. This is useful if, say, I want to measure the red signal input and the red signal output and compare them.

Sunglasses

These are a must if working with the LEDs on. The LEDs are deceivingly bright and can cause temporary blindness or a funny sensation in your eyes after looking at them - a bit like if you try to look at the sun.

Although not specific to SMD work, I find the following useful when working on anything:

“Pearl catcher” pick-up tool. This is useful for picking up small screws or, even better, holding small screws while you’re trying to screw them in awkward places, such as when fitting a drive into a drive bay with the PC upright.

Precision screwdrivers - use a 1mm flat blade screwdriver for adjusting the pots when calibrating the lights etc.

Connectors

The simplest connector is the “chocolate block” type with screw terminals. You will need one of these if you are removing the amplifier PCB and want to keep the subwoofer speaker connected.

Small container

Have one or more small containers to put the screws etc. in - seems obvious, but many times I’ve been hunting for screws that have disappeared within minutes of my removing them!

Notebook and pencil

Not strictly a tool, but this is a must. I always find that I need to make a note when I’m working on something, even if it’s just a reminder of what screws go where.

Connector links / Flexible jumper wires  

These are useful during testing etc.

Clamp

Some form of clamp is advisable to hold the PCB when soldering. It can also be useful during testing, but it is very important that any metal parts or clips on the clamp are isolated to prevent short circuits on the PCB. The clamp can either be a bench fitting type, or a PCB holder of the sort you see with various clips attached. Whatever you use, make sure that it will hold the PCB rigid. DO NOT OVERTIGHTEN the clamp on the PCB, especially if you’re using a bench clamp with jaws - you will damage the PCB. Personally, I prefer not to use a clamp while testing, but it is ideal for soldering when you need three hands!

See the Components / Where to buy page for further details about the tools