RE: Need Star Castle Help

Well.
        I know nothing about the PS in question, but typically on williams
power supplies, given that symptom here is what I would suspect....

        There are two major parts to the supply...a regulator (typically a
723) and a power transistor (darlington pair...or whatever). The regulator
sets the voltage to a particular level, and feeds that to the transistor.
The transistor then supplies the current neccesary to drive the circuit at
the given voltage. If the transistor cannot provide the neccessary current,
ohm's law says that the voltage will drop. So the regulator is probably
fine, but the transistor is baked.

        This is my experience on williams linear supplies, so your milage
may vary.

Mike

> -----Original Message-----
> From: Matt Rossiter [SMTP:matt@rossiters.com]
> Sent: Wednesday, October 07, 1998 2:35 AM
> To: Vectorlist
> Subject: RE: Need Star Castle Help
>
> OK - for those who may have read my previous post.
>
> I began suspecting my problem may actually be in the power supply. When
> I plug the Molex connector to the board - I'm only getting about .6v.
> When I unplug the Molex connector, I'm reading +6v from the pins. So my
> roommate suggested I connect a 5 ohm resistor to the pins which are
> supossed to be putting out +5v. If the voltage drops to 0v - then it's
> most likely to be the power supply. So I did - sure enough, the voltage
> dropped to 0v.
>
> So... when looking at the schematics for the power supply - my roomate
> suggested that the most likely candidate for a problem would be the
> large transistor (Q1). So I gave it the diode test. With positive lead
> on emiter and negative lead on base, I get a reading of 1.6v. With the
> leads switched I get .6v. I'm not exactly sure If this transistor is
> *the* problem. I guess I'll have to do some more probing around. If
> any Cinematronics experts out there have any further suggestions let me
> know....
>
>
> Thanks....
>
>
> Matt
>
> BTW - This is the first time I've tried posting on the vectorlist. If
> it's more "appropriate" to post tech help questions on rgvac - let me
> know.
>
>
> ****** <Previous Post> ******
>
> Perhaps someone can give me some direction with this Star Castle that
> I'm working on.
>
> The original problem was - The LED on the CPU board was staying lit.
> Which, I assume, is an indication that the game is stuck in reset mode.
> I was getting +5v across the board. Distorted sound was coming out of
> the speaker - and the CRT was glowing. No picture of course.
>
> So - I took a logic probe and tested all of the chips within the reset
> circuitry. Everything seemed good, except the reset pins were reading
> low instead of high. So - on the chip at A2 on the board - I tried a
> little experiment. I forced the reset pin to be high instead of low.
> This did indeed cause the LED to go out - but the game still didn't
> work. To make matters worse - somehow the circuitry shorted out. Now I
> only get .6v across the board. - Yup, I'm a greenie.
>
> So.... I need some expert advice on the following.
>
>
> 1) I have a logic probe, an Eprom Burner, a DMM. I probably should
> start becoming more familiar with a scope. Does anyone have
> recommendations as far as getting a nice scope to work with? - And more
> importatnly, does anyone have recommendations for any other tools that
> might be helpful? I would love to get the Cinematronics exorsizor - but
> I'd only be dreaming I suppose.
>
>
> 2) As far as the problem I mentioned above. Any suggestions as to
> where to go from here? I have the manual/schematics and can get any
> parts I need.
Received on Wed Oct 7 12:00:12 1998