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):
Removing the original dual diodes:
Removing the pair of original dual diodes is easy.
- Remove the two screws securing the two bridge rectifiers underneath
- Flip the board over and notice the mounting screws, and the other wimpy bridges
(See four screws and two pairs of soldered leads labeled "1" and "2")
- Remove all four phillips head screws
- Then remove as much solder as you can from the leadswith the desolder tool of your choice
(I'm using a really nice desoldering tool with an electric pump - real slick!)
- Then bend up the wires w/ pliers and remove more solder if possible
(picture and picture)
- You can then remove the devices and their heat sinks and now the board looks like this
Prepare the new bridge:
Next step is to prepare a modern bridge to fit in place of the two dual diodes you just removed. I like to use nice 35-Amp bridges. You can find them at most pinball vendors that sell electronics. Be sure to get one w/ wires, NOT lugs.
- So we don't mess up, label the board w/ a Sharpie like I did here
- Now take your bridge, noting the position of the notched corner, and bend the wires kinda like this
- Then lay it on the board, again noting the notch, and make sure the leads line up w/ the proper holes
(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)
- 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.
- Once all the leads are lined up w/ their corresponding holes, mark the wires so you know where to bend them
- Now bend the wires so they look like this
- Finally test the fit, again being damn sure you have each lead in the proper hole
(picture and picture)
Mounting the new bridge:
Now all you have to do is mount the new bridge, and you're all done!
- First off, mount a heatsink before you install the bridge, and use a little heat sink grease too
(sorry about the blurry photo)
- Then insert the wires IN THE PROPER HOLES, and tack-solder the two "AC" leads
- Before you solder it in place, take a look and make sure the 4 leads do not touch any PCB traces
- Flip the board over and bend the protruding wires flat against the circuit board
(Notice there are some empty holes - that's ok as we replaced 4 leads and 4 screws w/ just 4 wires)
- Solder the "+" and "-" leads first
(in the holes labeled "1" and "2"), then the two "AC" leads
- Then flip it back over and put some more solder on the two "AC" leads
That's it, your done. Here's a couple more photos so you can also see how I mounted two more bridges in place of the old VARO bridges, that I also removed. There are traces on both sides of the board so be sure you solder the bridge leads on both sides!
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!!!).
And finally an overall picture showing the completely rebuild board:
Created 2/25/05 - Last Modified 1/20/07 - Steve Kulpa
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