Re: {Collins} HF-380 Issues



This could be a switching issue on the filter board during transmit. Run a
trace on the RF (IF) signal and see if the path is open during transmit.
Check first to see if you have RF of the correct frequency approximately
going to the mechanical filter when mic audio (tone) is applied. Then see if
it comes out the goes out of port on the mechanical filter. You will learn a
lot about the filter status and the path switching when you do this. Then,
depending on if, and where, it is missing, you can go from there. That would
be my first point of entry.  You will also learn a lot about the balanced
mixer area in the process.

Let us know what you find.  Your assumption that the PA finals are good is
sound.

Regards,


Bill Carns, N7OTQ
Trustee K0CXX
President, Collins Collectors Association
Editor, Signal Magazine
Wimberley, TX
512 618 2762  (Cell)
512 847 7010  (Home)



-----Original Message-----
From: Collins [mailto:collins-bounces+wcarns=austin.rr.com@xxxxxxxxxxxxx] On
Behalf Of Michael Rioux
Sent: Sunday, July 13, 2014 9:50 PM
To: collins@xxxxxxxxxxxxx
Subject: {Collins} HF-380 Issues

Hello,

I recently acquired a HF-380 that had issues. A 'hack' had been through the
rig over the years and had done a pretty sloppy job of
repairs/modifications. When I received the 380 it did not work. After
plugging away at it over more than a few evenings and trying to clean up the
previous owner's mess (a club at a large West Coast defense contractor), I
got the rig to receive (bad tantalum on the 14v rail). It now sounds pretty
good, sensitive, and all of the major stuff works. But, I'm at the point now
where everything seems to be working except transmit. I have been going
through the circuitry page by page and have determined that the voltages
look good, and my limited oscilloscope skills have determined that there is
mic and cw sidetone input to the transmitter chain. I'm no troubleshooting
wiz and am looking for some guidance in where to go to next. I know that a
lot of the receiver and transmitter circuits are shared. My first guess was
to assume that the PA was blown. But, my wattmeter shows 100+ watts out when
the PTT or CW key is let up. I noticed that SB-18 addresses an issue with RF
bursts on key up. I also noticed that SB-12 is required to fix a related
issue and that both of these mods didn't appear to be made to the
receiver/exciter board (I'll get to them once I get the radio completely
working). So, I'm assuming at this point that the PA is good. Any HF-380
gurus out there that can point me in the right direction to get this beast
working? I'm really glad I haven't had to attack the synthesizer yet as it
works fine! That board really scares me!

Thanks a lot and 73,

 

Mike, W1USN

 

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