Re: Star Castle PS levels & display

Douglas Gauck wrote:

>Hi all,
>
>Hoping to get some help with the above. I've already replaced the caps in my
>Condor power supply and I get nice flat voltages coming out -- only instead
>of -25 and +25 they're -30 and +30. The +5 is right on as there's a pot to
>adjust it. How to bring in the other two? The SW1 jumper is set at 115, but
>the AC in my house is up at around 123v.
>
>
 

Only way to get the ±25 back to where it should be would be to get the
line voltage right. Shouldn't really matter, but if you REALLY had to
you could either buck it out with an 8 or 9 volt transformer or get
yourself a Variac® at a hamfest or eBay. Here's one that can handle a
dozen machines at once!
<http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2986449309&category=30082>
For only one machine a smaller, cheaper one will do. But this isn't
going to fix your problem.

>I am hoping this will help with my other problem, which is the entire image
>being offset towards the upper right corner of the display. Even points from
>the lower left quadrant of the screen end up drawn northeast of the
>center point. As the machine warms up, the image gradually drifts into the
>center until it's dead on. By this time Q105 and Q205 are piping hot, with
>Q104 and Q204 not far behind. Perhaps this is why I can only do this so many
>times before the main deflection transistors Q110 and Q111 give up and start
>popping breakers.
>
>

You really need to unplug the YOKE (NOT the output transistors) so you
don't blow up anything while troubleshooting.

>Any ideas? I've already replaced all the diodes and tested the transistors.
>Swapping DACs and the LF13331 had no effect. Could the 7815/7915s be at
>fault? They run warm, which I chalked up to the +/-25 supplies being high,
>but their outputs looked good.
>
>

You need to check the +15, -15, and +5 regulators on the monitor and
make sure they're doing what they should. I would think one of those
has to be drifting.

The general idea is that something affecting BOTH channels will be a
part that's common to both channels, like power supply parts. Digital
usually either works correct or doesn't, your "gradually drifts into the
center until it's dead on" just screams analog, not digital. What
you're talking about sounds a lot like a DC offset. As far as your hot
transistors are concerned, The design puts about .5 watt into those.
Unless they are large parts or heat sunk they are going to run toasty.
A half a watt doesn't sound like much, but a small transistor really
doesn't get rid of the heat all that well and will get quite warm. I
suppose the increased voltage could be breaking those transistors down.

Another way to troubleshoot this is, if it has run long enough to get
the picture normal, to use a little freeze mist on a part at a time
until the picture drifts back out.

>I also have intensity, blanking and spot killer issues! Thanks,
>
>

I wouldn't worry much about that until you get the rest fixed, these
points might straighten out with the rest of it.

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Received on Mon Feb 16 02:31:51 2004