Reply-To: "Dave M"
From: "Dave M"
Subject: Re: Help with a circuit
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
Date: Fri, 18 Oct 2002 23:57:50 GMT
NNTP-Posting-Date: Fri, 18 Oct 2002 23:57:50 GMT
Organization: AT&T Worldnet
My first response to your post is... did the circuit ever work correctly, or
is this an experimental circuit that you're trying to build? By virtue of
C10 and C11 becoming hot, I am immediately suspicious of the design. After
their replacement, did they continue to run hot?
Assuming that the circuit is of good design and was working previously, wd
need to make some voltage measurements to determine the defective part(s).
What's the voltage at the colector of TR3? If it's about 24 volts, then we
can assume that R15 is dropping a lot of voltage due to higher than normal
current through it. Have you disconnected the load on the +68V output to
see if it comes up to the right voltage? If it comes up to +68V, then I
have to say that the most likely cause of failure is in the load, not the
While you're measuring voltages, measure and record the voltages at TR3
base, TR1 base, TR1 emitter and the junction of C10 and R15, both with the
load attached and without.
Report back with the results of those measurements and we'll go from there.
Dave M email@example.com
Remove the xx for my correct email address
"Craig Atkins" wrote in message
> Please help me!!
> This circuit: http://www.sire.co.uk/circuit.jpg
> is not working as it should.
> The input voltage at pin 9 is 90/100 VAC.
> The output voltages are all correct, apart from pin 4, which is giving
> out about 24VDC as opposed to 68VDC.
> The resistors R14 (10W) and R15(10W) both get very hot (understandable
> i guess, as they are 10W ceramics).
> The capacitors C10 and C11 used to also get very hot, but I have since
> changed these parts.
> I have also replaced TR1 and TR2.
> I am now stuck, due to my rather limited knowledge of electronics. I
> think that maybe TR3 isn't working right, but I'm probably way off
> Could anyone suggest which parts may be faulty and causing this
> voltage error?
> Thanks in advance!