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<DIV>In a message dated 2/1/2011 2:13:07 P.M. Pacific Standard Time,
lwiederh@worldpath.net writes:</DIV>
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<DIV><FONT size=2 face=Arial>Can anyone guide me to source of IC 442-626
MFC6030 or 78MGT4 for SB-104 Power Supply? Unavailable at Mouser, Digikey and
Newark.</FONT></DIV>
<DIV><FONT size=2 face=Arial>Thanks for any help.</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Lou
Wiederhold</FONT></FONT></FONT></DIV></BLOCKQUOTE>
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<DIV>I tried to find this IC about 5 years ago with no luck. Only
suppliers were surplus wholesale outlets, and you couldn't buy just one.
When the IC blew on my HP1144 PS here's what I did:</DIV>
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<DIV>Replace (within the SB-104) IC202/Q1and associated circutry with a
fixed three-terminal 5V regulator, freeing the IC for use in the PS. If you
use a LM7805K (aka LM340K-5) it has the same physical form as Q1, a TO-3
transistor. You can ground it to the chassis for a good
heatsink. These regulators are also obsolete, but back in the day of TTL
logic almost every PC board had one on it, so they're not hard to find. If you
can't find the TO-3 regulator you can use the more common LM7805T which is
TO-220, but you'll have to figure out how to mount it. This mod is actually
better than the original circuit. The three terminal regulator provides
more accurate and more stable voltage than did IC201/Q1. Before I made
this mod, I blew a few TTL ICs on the SB-104 before discovering the IC202/Q1
voltage was about 5.5V, not 5.0V as prescribed. I blew IC101 which is
also obsolete! This is because R252 and R253 are 10% resistors whose values are
prone to change with time.</DIV>
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<DIV>The reason the IC blew in my PS was the computer-grade
capacitors became leaky with age. This put an added strain on the IC
trying to regulate the voltage. You should check this out. BTW,
computer-grade caps are easy to find surplus. </DIV>
<DIV> </DIV>
<DIV>A year later, Q3 blew on the PS. This again killed the
IC. I bit the bullet and did a total re-design of the regulator
circuit using a LM723. </DIV>
<DIV> </DIV>
<DIV>The HP1144 PS has a serious design flaw: It has no over-voltage
protection. If you blow one of the RF finals in the
SB-104 you'll have a helluva time replacing it, they're obsolete too. And
theoretically if you blow one, you have to replace all four! You should
seriously consider adding this feature, it only takes a SCR and a few other
parts. </DIV>
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<DIV>Chris, KL7DM </DIV>
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