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From: harrism@dg-rtp.dg.com
Newsgroups: rec.ham-radio,sci.electronics
Subject: Radio Service Question (contd)
Message-ID: <2200@xyzzy.UUCP>
Date: 13 Jan 90 23:59:01 GMT
Sender: usenet@xyzzy.UUCP
Reply-To: harrism@dg-rtp.dg.com ()
Distribution: usa
Organization: Data General Corporation, Research Triangle Park, NC
Lines: 30

Howdy. I'm working on my ICOM-701 hf transceiver. I've pinned the potential
source of the "funny popping noise" to Q37 on the A board. It is
a pass transistor for the receive mode +9v. It is running *VERY* hot to the
touch - you can't keep your finger on it. 

The noise starts up when the transistor gets hot - about 20-30 seconds after 
power up. It is a tall plastic transistor. The complementary transistor for 
xmit is a power transistor with a 1sq inch heat sink attached.

The "noise" isn't present on the inputs to the transistor.

Soooo, Questions:

1) Has anybody had similar problems with their IC-701 (or any radio?) Is this
a known IC-701 failure mode? BTW, I have found other components in the rig 
that are being pushed hard.

2) Is it probable that this transistor is shorted and/or bad?, or,

3) Some other circut is being a pig and overloading this transistor. (All
circuts seem to be functioning properly excepting this "noise") I haven't
had a chance to measure the current this transistor is passing. 

4) Anybody have specs on this transistor? It is a 2SD468. How about an xref
for substitution?

Thanks, Mike.

Mike Harris - KM4UL                      harrism@dg-rtp.dg.com
Data General Corporation                 {world}!mcnc!rti!dg-rtp!harrism
Research Triangle Park, NC