Rebuilding a Bally AS-2518-49 Power Supply

Clay's excellent Bally Repair Guide already tells you everything you need to know about rebuilding a Bally AS-2518-18 Rectifier board, including how to replace the whimpy original VARO bridge rectifiers with heavy duty modern bridge rectifiers. When Bally upgraded the rectifier board with the introduction of the AS-2518-49 module, they replaced BR1 with a pair of dual diodes, each mounted in a TO-3 can, much like a power transistor. BR1 rectifies the voltage used for the controlled lamps and was a constant source of problems on the original -18 module. It often would overheat and then become damaged and eventually fail. The VARO 712E dual diodes were probably the only heavy duty diodes available at that time (20 Amps I think) so I assume that's why they were used. Each one consists of two diodes and they are configured such that combining them it the proper way makes a standard bridge rectifier.

Find and dandy - fast forward to 2005 - these dual diodes are now impossible to find. The good news is that they are a lot better then the original piece of crap orginally used on the -18 board, but in the event they do fail, you're in a jam as there are just none to be had. I found myself in just that situation so what I did was take a modern heavy duty bridge rectifier, with wires, and with a little creative bending of the wires, I was able to retrofit this device on the board in place of the two duals in such a way that it worked perfectly.

So, if your -49 is showing symptoms of a bad set of dual diodes (readings nowhere near 6.5VDC at TP1 or other problems with the overall performance of the controlled lamps), all you have to do is get a nice 35 Amp bridge with wires, and do the same thing I did, as I illustrate below, but first, a before and after picture (besides replacing the duals, I also completely rebuilt this board with new bridges for BR2 and BR3, plus all the other components):

Before

After

Removing the original dual diodes:

1. Remove the two screws securing the two bridge rectifiers underneath (picture)
2. Flip the board over and notice the mounting screws, and the other wimpy bridges (picture)
   (See four screws and two pairs of soldered leads labeled "1" and "2")
3. Remove all four phillips head screws (picture)
4. Then remove as much solder as you can from the leadswith the desolder tool of your choice (picture)
   (I'm using a really nice desoldering tool with an electric pump - real slick!)
5. Then bend up the wires w/ pliers and remove more solder if possible (picture and picture)
6. You can then remove the devices and their heat sinks and now the board looks like this (picture)

Prepare the new bridge:

1. So we don't mess up, label the board w/ a Sharpie like I did here (picture)
2. Now take your bridge, noting the position of the notched corner, and bend the wires kinda like this (picture)
3. Then lay it on the board, again noting the notch, and make sure the leads line up w/ the proper holes (picture)
   (The "+" lead lines up w/ the "+" hole, the "-" lead lines up with the "-" hole, and the two "AC" leads line up with two of the screw holes)
4. The step above is VERY IMPORTANT, so double check that the notch positioned as shown, and double-check the labels on the bridge to be sure the "+", "-", and "AC" leads are in the proper position.
5. Once all the leads are lined up w/ their corresponding holes, mark the wires so you know where to bend them (picture)
6. Now bend the wires so they look like this (picture)
7. Finally test the fit, again being damn sure you have each lead in the proper hole (picture and picture)

Mounting the new bridge:

1. First off, mount a heatsink before you install the bridge, and use a little heat sink grease too (picture)
   (sorry about the blurry photo)
2. Then insert the wires IN THE PROPER HOLES, and tack-solder the two "AC" leads (picture)
3. Before you solder it in place, take a look and make sure the 4 leads do not touch any PCB traces (picture)
4. Flip the board over and bend the protruding wires flat against the circuit board (picture)
   (Notice there are some empty holes - that's ok as we replaced 4 leads and 4 screws w/ just 4 wires)
5. Solder the "+" and "-" leads first (in the holes labeled "1" and "2"), then the two "AC" leads (picture)
6. Then flip it back over and put some more solder on the two "AC" leads (picture)

All Done!

Also, notice how I mounted the power resistors so they are raised up above the board just a little bit. Look again at the 2nd picture above and you can see the scorching left by the original resistor, that was laying flat against the board. Raise them up a bit to allow for better air flow (these suckers get HOT!!!).