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<DIV><FONT size=3>Hi Lee:</FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>Chris covered the basics, but because t</FONT><FONT size=3>he
supplies are shunt regulated, if you have too LITTLE load on the supply, the
excess is burned up as heat. As he mentioned, if the machine has been
reconfigured in any way, the supply may no longer be properly set up.
There are several possibilities, and they may be somewhat differently
implemented, depending on the version of your machine. The standard supply
includes a resistor which is shunted depending on the load, and generally
determined by a jumper in the machine wiring harness, and that's what may be
done in different ways depending on the original factory configuration of your
machine.</FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>For high current operation, the jumper (wherever it is in the
system) will produce a short across J6-20 and J6-18. This is easy to
measure using the power supply extender cable. If it is shorted, locate
the jumper and remove it. If the supply will still provide +/-12, then you
will find that it will run much cooler. On some of the machines that we've
refurbed, we've used a different resistor to properly balance the load.
The ultimate goal is to have the shunt regulators doing very little so that they
run cool and last a long time!</FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>Another thing you may need to check is your line
voltage. The supplies were generally strapped for 115 VAC at the factory,
and today, that's probably not correct.</FONT></DIV>
<DIV><FONT size=3></FONT> </DIV>
<DIV><FONT size=3>Don Norwood<BR>Digitrak Communications, Inc.<BR><A
href="http://www.digitrakcom.com">www.digitrakcom.com</A></FONT></DIV></DIV>
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style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: black"><B>From:</B>
<A title=Chill315@aol.com href="mailto:Chill315@aol.com">Chill315@aol.com</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=quadlist@quadvideotapegroup.com
href="mailto:quadlist@quadvideotapegroup.com">quadlist@quadvideotapegroup.com</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Tuesday, June 28, 2011 5:15
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [QuadList] Ampex VR1200
power supply question</DIV>
<DIV><BR></DIV><FONT id=role_document color=#000000 size=2 face=Arial>
<DIV>Lee</DIV>
<DIV> </DIV>
<DIV>There are a couple of things to check. </DIV>
<DIV> </DIV>
<DIV>First are the air filters clean below the power supplies? Very
important for cooling.</DIV>
<DIV> </DIV>
<DIV>Second, are all the fans turning? Pull the filters and use a small
mirror to check. These have a tendency to stop or get so sluggish.
Or you can pull all three supplies and see if they are turning. The
first method is easier other than for us old folks having to get down on the
floor.</DIV>
<DIV> </DIV>
<DIV>Third, are the shunt resistors strapped correctly. If you have
added or removed any accessories, this can cause a problem. So if you
have disconnected the Editor, Erase amplifier, or other items, follow the
procedure in the manual.</DIV>
<DIV> </DIV>
<DIV>Lastly, check the capacitors in the supply, signal system, and Intersync
to see if you have an issue there. There might be a load on the +12 volt
side that is drawing more current.</DIV>
<DIV> </DIV>
<DIV>Chris Hill</DIV>
<DIV>WA8IGN</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>
<DIV>In a message dated 6/28/2011 3:05:20 P.M. Eastern Daylight Time,
lasvegastvengineer@yahoo.com writes:</DIV>
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<DIV>I have been working on a VR1200 and noticed that the +12V power
supply transistors run noticeably hotter than the -12, 24 and 135
transistors. </DIV>
<DIV> </DIV>
<DIV>Is this normal for a 1200? </DIV>
<DIV> </DIV>
<DIV>Thanks </DIV>
<DIV>Lee
</DIV></TD></TR></TBODY></TABLE><BR><BR>_______________________________________________<BR>Please
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