The linear power supply board designed by Gottlieb had a number of different design revisions and those are outlined below.

MA-303 "Revision 1". This power supply board, although never officially denoted as the first revision, was shipped with Reactor and Q*Bert games. This board supplies power to the main PCB, the sound board, and in the case of Q*Bert, to the knocker solenoid. The power supply board also provides a ground for the self-test switch, and joystick switches.

This first version of the power supply board provides +30VDC to the sound board in order to drive the LM379 Audio Amplifier, and the same +30VDC to actuate the knocker solenoid. This power supply board will work with Reactor, Q*Bert, and Mad Planets CPUs and sound boards. This power supply board will NOT work with a Krull sound board, as it only expects +16VDC. If you use this power supply board with a Krull sound board, you will damage the sound board!

As a point of fact, this power supply board generally runs +34VDC into the audio amp. No wonder they often fail! While running the amp at +34VDC might not be the best course of action, other components in the power supply circuit (namely the 30V zener diode D26 and resistor R23) add to sound board dysfunctions. If the diode shorts, it ends up running +43VDC through the sound amplifier circuit damaging many things in its path.

However, there is an easy fix for this design flaw. The LM379 audio amplifier gets its +30VDC from a rather inefficient voltage regulator that gets a voltage reference from a zener diode, which then amplifies the current through a 2N3055 transistor. The problem is, the output voltage is higher than you might think. The original 1N5363B zener diode was rated for 30 volts. It is a good idea to remove it and replace it with a five-watt zener diode rated for 25 volts or 24 volts. Alternatively you could use a 27volt, 10-watt zener diode.

MA-430 "Revision 2". The second revision power supply board was used in Mad Planets (the third game to be released by Gottlieb). This power supply board only had some minor changes, which can be noted in the schematics. Fuse 21 was upgraded to 2 amps, the location of resistor 11 was changed, and Fuse 41 was rerouted to the input of D41. +30VDC was still supplied to the sound board, but since there was no knocker, that portion of the harness was not used.

MA-492 "Revision 3". The third revision of the Gottlieb power supply board was utilized in all Krull games. After a number of LM379 audio amplifier failures on the sound board, Gottlieb redesigned the audio amplifier section with a small daughter board that utilized a lower power amp which only required +16VDC. Again, since there was no knocker solenoid, this power supply board was modified to produce lower voltages and therefore runs cooler. The following changes were made to the Krull power supply board:

• C22 (one of the big blue capacitors) was removed
• D26 was changed to a 16V, 5%, 1W diode (1N4745A)
• F21 remained as a 2 amp slow blow fuse
• R21 was removed
• R23 was changed to a 1K ohm, 5%, 2W resistor

You could conceivably use this Krull power supply board to power a Reactor or Mad Planets CPU and sound board, but the +16VDC is not enough to power the Q*Bert knocker solenoid. You could, however, replace the knocker solenoid with a +12V version and everything should work just fine.

MA-479 "Final Revision". This final revision of the power supply board came standard in all M.A.C.H. 3, Us vs. Them, and Three Stooges games.

Power Distribution from the May/June 1983 issue of Gottlieb's "On Target" Technical Newsletter
How to convert your Gottlieb game to a switching power supply.

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