Re: Maybe stupid Asteroids question!

Joel Rosenzweig wrote:

>Hi Martin,
>
>It's been a while since I've done this, but you can hook your DC power
>supply directly to the output of the voltage regulators that are on the
>Asteroids board. The AC was used to provide both + and - 15V DC on the
>board. If your DC supply sources these to the right spot (i.e. post
>regulator) you'll be OK. You'll still need to hook up +5DC as normal. I
>forget if it uses +12 as well, but if it does, you'll need to hook that up,
>too.
>
>Some people may freak out by the notion of hooking up the +/- 15 VDC post
>regulator, but I did this with my Asteroids board for hours and hours at a
>time with zero problems at all. If you're worried about the regulators,
>then remove them from the PCB while you do this. I found it to be
>unnecessary, but your mileage may vary.
>
>Joel-
>
>

Well, since I'm invited to freak out I guess I will.

If a regulator has filter capacitors on its input it can be damaged by
applying the output without an input. The exception is if a protection
diode has been added from the input to the output. This diode is an
extremely good idea in any circuit using a 3-terminal regulator but
engineers sometimes leave it out (they can't apparently read the
application notes and warning for the part.)

To supply all those voltages may take one hell of a lot of power
supplies and is risky. And some ICs may be damaged if the positive
supplies are turned on before the negative supplies. The old 4116 RAM
used on Williams boards is infamous for that, but some opamps can have
the inputs blown out if the inputs are directly grounded (another no-no
for designers, a grounded input should go through a resistor equal to
the impedance of the other input---but that is mostly for better thermal
tracking of the inputs so it get left out on some designs). Long story
short, if you must use separate supplies bring up the negative ones
first or ALL at the same time.

End of freak out.

>----- Original Message -----
>From: Martin White <martin@guddler.co.uk>
>To: <vectorlist@synthcom.com>
>Sent: Sunday, December 15, 2002 2:21 PM
>Subject: VECTOR: Maybe stupid Asteroids question!
>
>
>
>
>>Hi guys,
>>
>>First post in a very long time!...
>>
>>Anyway, i have an Asteroids board and two Ast. Deluxe boards here that
>>i've just got as non working. My cabinet (an Asteroids mini) is
>>currently on it's hol's in a foreign country having it's woodwork
>>lovingly restored, so i need to make up some kind of rig for getting
>>these going.
>>
>>Picture is no problem as i can use my scope, but i am unsure of what i
>>need to do about the 36v AC...
>>
>>Is this really needed? If so, how do people provide this? I'd rather not
>>start getting hold of spare power bricks and AR boards just for this
>>purpose as my test bench is full enough already!
>>
>>Is it 18v Center Tap with each side going to one pin on the edge
>>
>>
>connector?
>
>
>>My rig (http://www.guddler.co.uk/taitorig.php) has the usual +5, -5, +12
>>DC, but it also has -12, 26, 20, 15, 14v (DC) and 10.6v AC (21.2v CT?)
>>would any of these help rig it up?
>>
>>If no to all the above, i am told that i can get a toroidal PS from
>>www.maplin.co.uk - anyone recommend a stock number and how it should be
>>connected up?
>>
>>Thanks for any info,
>>
>>Martin.
>>--
>>Guddler's Arcade
>>http://www.guddler.com
>>--------------------------------------------------------------------------
>>
>>
>-
>

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Received on Sun Dec 15 19:39:46 2002