Asteroids repair log 2 - power supply

Back again, I forgot to mention the mods to the Audio/Regulator
board that will help against further board and power supply problems,

As you probably already know, the Audio/Regulator board
(and 'II' version on later games) uses seperate +SENSE (5V sense)
and -SENSE (GND sense) lines that are expected to go to the
game pcb, and feedback the voltage at the game PCB so the regulator
can adjust the power supply up a bit to allow for the voltage drop
of the connectors and cabling.
Of course 20+ years and low quality connectors to start with meant the
voltage drop gets higher quickly, and causes all kind of voltage
regulator, burn out and voltage offset, video wobble and other weird problems.
Also, failure of the Regulator circuitry or pass transistor has
the ability to put over 10VDC at high current into the 5V rail
of the game board, which can kill many parts!

To fix this problem,
 (AUDIO/REGULATOR board, not AUDIO/REGULATOR II, fix is the same but pinouts
  and parts locations may be different?)

 1) First check the board is adjusted to 5.00 VDC output
    while still in the machine.
    This is because a later step will fit a 5V6 zener to the output, and
    it should be below that before fitting it!
    If you find the R8 1K pot that adjusts this is a bit jumpy or touchy,
    replace it with a good quality cermet trimpot, it will save some
    power supply trouble later.

 2) On the back side of J7, the 9 pin connector, you will see pins
    1 and 4 are connected together.
    Short with a piece of wire soldered to the back, Pin 2 to Pins 1&4.

 3) On the back side of J7, the 9 pin connector, you will see pins
    5 and 6 are connected together.
    Short with a piece of wire soldered to the back, Pin 3 to Pins 5&6.

    Resolder all the connector pins on the PCB just for good measure, they
    can go dry or mechanically bad.

 4) Remove CR1, the diode closest to J7, after first noting its orientation.
    (you could leave it in and put the zener over the top of it if preferred)

 5) Solder a 5V6 5W (or higher wattage) Zener diode at CR1, with the
    stripe facing the same way as CR1.
    I use an 1N5339B 5V6 5W zener.

 6) If you have a bench power supply, put 10-12VDC into the +10.3VDC UNREG
    input (with GND), current limited if available to 200mA, and check and
    adjust the 5V output to 5.00 VDC with the 1K pot.
    If you don't just plug it in to the machine with the game board
    unplugged, and adjust the output very carefully to 5.00VDC.
    NOTE! If you accidentally adjust over about 5.6VDC the zener will start
          clamping, get hot, and the fuse for that line may blow.

Don't hesitate to replace the edge connector that goes to your game board
if it's a bit loose, it can save a lot of drama.
Mark the new connector so you know which way is the 'top/parts' side.
'Prime' with solder all the pins of the new connector, so they are ready
 to accept the new wire ends
One at a time, cut the wires off the old connector, strip, prime with
 solder the stripped end, then hold the wire and the iron to the new
 connector pin, and it will attach easily.

Best regards,

Marc

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Received on Tue Jul 1 09:00:17 2003