Power Supply Tips

1. Is it plugged in?
2. Are all the fuses OK?
3. Is the Power Supply generating ALL the proper voltages?

Unfortunately, upon reaching a positive conclusion to the above three explorations, most technicians stop right there and move on to attempt to fix the apparent problem. Power supplies are often overlooked as contributors to intermittent and annoying problems.

The first thing I do when I get a "new to me" pinball machine is totally rebuild the power supply. This may seem like overkill and an excessive expense to some, but in the long run this action will save you countless hours of grief and dollars at some time in the future.

In explanation, all power supplies contain capacitors and most all capacitors dry out over time. When that happens, the capacitors ability to filter the AC (alternating current) component from the DC (direct current) becomes diminished. This diminished "capacity" eventually ends up in component failure, notably the power supply regulators and zener diodes. Eventually the regulator failure will be accompanied by a physical explosion of the capacitor, a smelly and messy proposition at best. On a more subtle note, the increasing amount of AC on the DC lines (like the +5 and +12 volt power supply rails) will, most likely, cause serious damage to your MPU and Driver boards long before the "ticking time bomb" (and I'm NOT referring to your battery - that's another problem I won't cover here) goes off in your backbox. If you're lucky (?), all you'll lose is the regulator transistors and maybe the zener diodes on your Power Supply board. This can all be avoided with a little "Preventative Maintenance" to your Power Supply.

Pinball machines were never intended to have a life span of greater than about 7 or 8 years and were built accordingly. Most components are "bottom of the line", circuit boards are of fairly low quality, and the whole thing was made to be disposable. Inexpensive capacitors are going to have a life span of about 10 years or so, sometimes less, occasionally more. The only way to know for sure if a capacitor is bad is to check for AC "ripple" with an oscilloscope, not an option for most pinheads. But that still doesn't give any guarantee of future life-span. Personally, I gave up the practice of using a 'scope on power supplies some time ago as it is cheaper and faster to just replace Power Supply components with new ones. Besides, doing a wholesale changeout gives you the equivalent of a "new" Power Supply, and one less thing to worry about.

1. You should try to use the same value and voltage as the original. It is allowable to use a higher (35 volt vs. 25 volt) voltage rating capacitor than the original, if it still fits in the original space. Most "new manufacture" capacitors will be available in the same package size as the originals, but probably with higher voltage ratings. It is also allowable to use a higher capacity rating (470uf vs. 330uf) capacitor in power supply applications only, if it still fits in the original space. Don't go too much larger, it could cause other (non-fatal, fortunately) problems.

2. Use the same type capacitor as the original. There are two "styles" of capacitors, one with "axial"leads and one with "radial" leads. The "axial" type has the leads coming out of oth ends of the capacitor body, and the "radial" type has both leads coming out of the same end of the capacitor body, so that it will stand up on a PC board.

3. Electrolytic capacitors (the type used most commonly on Power Supply boards) are polarized, that is to say that there is a positive and a negative terminal. DO NOT install one BACKWARDS! I guarantee that it WILL EXPLODE! And it won't be pretty. Always refer to the silk screening on the Power Supply board or the component layout in the manual. If in doubt, compare to another (preferably working) supply board.

4. ALWAYS install "axial" lead capacitors with the value markings in the "up" position. It will make future troubleshooting and identification much easier.

1. Use the same type of transistors (or voltage regulators) to replace existing ones. Marco Specialties, Wico, and the Liz all stock original type replacements.

2. Make a careful note of the lead placement. A transistor installed backwards does not get a second chance - it will blow instantly on application of power.

3. If there was an insulator under the mount of a transistor, be sure to install one on the new one. Also look for insulating bushings on the mounting screws. This is a common mistake made when the regulators are replaced on the GTB Sys 1/80 Power Supply. The devices will fail instantly if the insulators are not installed.

1. DO rebuild the High Voltage section of the Power Supply. DON'T hunt around for the high voltage parts. DO buy HV rebuild kits from Marco or the Liz. It's not worth the cost of a display to NOT rebuild this part of the Power Supply.

2. Inspect all the connectors. Replace any that are corroded or burnt. Also replace the mating connector at the same time.

3. Install an inline fuse holder in the line from the transformer to the bridge rectifier. Williams didn't put one in until after FIRE!, and not having a fuse increases your risk of fire if you don't have one. An 8 amp slo-blo will do the trick. Auto parts stores and Radio Shack have the fuse holders or you can get a kit with instructions from the Liz.

1. Don't forget about the Rectifier Board in the lower right of the backbox. For some unknown reason, I've had to replace the rectifiers in almost every Bally game I've ever had or worked on. Also, don't forget to use heat sink compound when you remount the board. Failing to do so will doom your new rectifiers to a premature death.

2. Don't be cheap - replace that BIG capacitor on the board. Yes, I know its going to be expensive, but consider what it will cost to fix your fried MPU board.

3. Inspect all the connectors and replace the bad ones along with the mating ones.

1.Consider remote mounting the 5 volt regulator. Get a TO-3 style heat sink and mount the regulator above the power supply. Your power supply will run cooler and be easier to service.

2.Don't forget the insulators under the TO-220 regulators.

1. Put a sticker on the Power Supply with the date it was rebuilt.

2. Check all the voltages. Make sure that they are within tolerances.

3. On supplies with adjustable levels, set them with a Digital Voltmeter. Set as close to the specified value as possible with all other boards unplugged. Check voltages again with the other boards plugged in and re-adjust if necessary.

4. If you got this far and are still confused, ask for HELP! Your Power Supply is the heart of your machine. If its not right, the rest of your pin will NEVER be right.