This collection of basic assembly instructions apply to the assembly of the repair switcher (circuit board shown below). At one time, I sold the completed switchers but it was too time consuming to assemble them. Since there is still some interest in the switchers (particularly from those who purchased the repair tutorial), I'll make the boards available for those who want to build it. The boards are 9.3"x5". They are printed in double-sided FR4 material in 2oz copper. The boards have a full silkscreen legend.
Here is the parts list in Excel format. Switchers with these components have been used for years and are known to be reliable. If you choose to use other/cheaper components, reliability may suffer.
The next 5 images show what the switcher will look like when finished if the recommended components are used.
I will not cover a lot of common sense safety items. This set of instructions assumes that you are at least capable of using basic hand and power tools and a soldering iron without doing serious bodily harm to yourself.
To assemble this switcher, you will need the following tools:
#1 philips screwdriver
Drill and the following drill bits 1/4", 7/32", 7/16", 1/2", 1/8", 5/16", 9/64"
Center punch and hammer (or an automatic center punch)
1 3/4" hole saw
Good quality soldering iron and solder (a cheap soldering iron will make the job much tougher - Weller WP35 or WES-50 recommended)
3/32" allen wrench for board/resistor mounting screws
Since it's likely that you've already purchased the components (most people order the board and the parts at approximately the same time - you should have been given a parts list when you ordered the board), the first stage of the assembly is to install the components into the bare circuit board. We will start with the smallest components. Below you can see the board where I've already installed all of the 1/4 watt resistors and the small diodes. To make this easier, I've chosen a resistor value that would work for all applications. It's a 2.7k Ohm resistor (red-violet-red-gold). The resistors have no polarity and can be installed without concern for their orientation in the board.
The diodes have to be installed the correct way to insure proper operation. The striped side of the diode goes to the square solder pad. In the following image, the two diodes would be orientated with the striped end facing to the top of the image.
It's important that you make good quality solder connections. Sometimes the flux in the solder will prevent you from determining the quality of the solder joint. To assure that you have good connections, removing the flux with acetone and a toothbrush will allow you to see precisely what you have. Remember that acetone is extremely flammable. Clean the board where you have good ventilation and allow the solvent to evaporate completely before soldering on the board. The following images are before and after cleaning.
The following image will help you to get the parts in the correct positions. It's a Flash file so you can right-click and zoom in on the image for slightly more detail.
Although it's difficult to see in the previous image, the 5 ohm resistors have their exposed windings facing the 2 ohm resistor. These resistors have an adjustable tap that can be used to change the resistor's value. For best reliability, I suggest removing the tap and using the resistor at 5 ohms. 5 ohms is perfectly fine for virtually all troubleshooting. If you want to bench test an amp at some specific ohm load, I'd suggest that you use external high power dummy loads. Use the internal resistors for low to mid power troubleshooting. The next 2 images show the resistor with and without the tap. Of course, if you wanted to use the tap, the paper would have to be removed.
The next two images give you a better look at the way the resistors are wired to the circuit board. The wire is a 12AWG uninsulated solid wire. The wire has no insulation to melt (if the resistors overheat) and they also provide support (although it's not really needed). If the solid copper wire you have is not shiny, use some sort of abrasive (sandpaper or scotch-brite type pad) to remove the surface oxidation.
Wiring the Volume Pot:
To connect the potentiometer to the board, you can use virtually any type of wire. I prefer to use a piece of ribbon cable from an old PC IDE cable. It makes the wiring simple and neat looking. Below, you can see the Radio Shack potentiometer.
The next image shows the pot after the terminals have been tinned. You can see that the ribbon cable has also been stripped and tinned. When tinning the terminals, take care not to apply so much solder that it drips into the potentiometer.
This photo shows the wires soldered to the terminals of the potentiometer.
This is the pot installed in the enclosure. The wires are tucked out of the way of the 100 ohm resistors (which could become hot and melt the wire's insulation).
The RCA connectors on the parts list are from a different manufacturer than the ones for which the RCA parts layout (on the circuit board) was designed. The mounting posts on these jacks are very slightly larger than the others. I suggested these because it didn't require that you order from a second supplier (which saves shipping costs). To get the jacks to fit properly, you may need to trim/chamfer the posts slightly (as seen on the right-most jack in the following photo). If you don't mind paying shipping for the other jacks, the part number is 161-4220. The distributor is Mouser. The Mouser jacks are still going to be tight but that's to provide stability.
As a side note... in general, you will never plug/unplug the RCAs unless you're replacing them. If you are going to plug/unplug the cables on a regular basis, I'd strongly recommend that you apply an adhesive such as Goop to provide more stability. The adhesive would fill a triangular area from the top of BACK of the jack to the board.
Templates:
To insure that you get the case drilled properly, I've provided the following templates. They will open in new browser windows. If you have trouble reading part of it, use the right-click to zoom in. Use the button in the applet to print the file. Double-check the measurements in the image against the printed version to be sure that it printed properly.
The following image shows the bottom half of the enclosure with the RCA drill template in place. Read the notes on the template before drilling.
This one shows the fan template after I drilled the pilot holes. Do yourself a favor and don't drill the top holes. They are not going to be used (the fan will be mounted with only two screws).
Fan Mounting:
The following images show the fan bolted into the enclosure. I used two #6x1" screws. These are available from most any hardware store.
This shows the electrical connection for the fan. I've provided two bare areas to which you'll solder the wire. Tin both the wire and the board before soldering the wires to the pads. Be careful not to apply so much solder that the pads become shorted together.
In this close-up, you can see that the fan is held off of the enclosure by two fiber washers on each screw. Moving the fan away from the opening reduces the noise produced by the fan. You can also see that I attached two rubber bumpers to the top of the fan. When you use washers that are (in stacked combination) slightly thinner than the rubber bumper, the bumpers will maintain pressure against the upper half of the enclosure. The bumpers reduce the vibration of the fan and therefore reduce noise.
Operations Manual:
If you haven't read the operations manual, click the link below.
The following image shows a sample cable that you could use to connect an amplifier to the switcher. As you can see, the cable has a connector that allows a quick disconnect so you can change from one adapter to another (for different brands of amps). In the photo, I've used only a single power and ground wire. For best results, you would use at least two power and ground wires in the cable assembly. This would allow you to run amplifiers at somewhat higher power. Of course, for high power testing, you'd use external power and ground connections and an external dummy load.
External Fan Control:
The switcher is able to control an external fan for your high power dummy load. The external fan is driven on whenever the internal fan is switched on when the internal dummy load is selected for the test piece. If it's annoying that the external fan comes on when it's not needed, you can wire in a second switch to make/break the connection to the external fan. The trace was intentionally narrowed to allow it to be cut easily. You would solder the wires for the switch into the pads/vias at the ends of the trace that you cut.
