Hi Larry,
I have seen that document before, but I just want to fix the R-725 as it
was originally designed for the moment. I may chose to improve things in
the future. I do have a R-390-a I need to eventually try to figure out
what someone did to it. I think someone tried to improve the AGC, and
add a product detector, and what they did in reality was create a very
poor preforming radio. I just do not really have the time or the
experience at the moment to try to figure it out.
Thanks,
Geoff
On 11/9/2024 10:03 AM, Larry Haney wrote:
Hi Geoff, Welcome to the R390 group and reflector list forum.
The R725 has essentially the same IF deck as the R390, which means those
and the R390A have the same AGC speed circuit - bad. Yes, you are right
in that those 2 caps are the problem, and it might be just 1 of them,
but you should replace both of them. The caps you replace them with
must have '0' current leakage (usually electrolytics don't qualify).
Your symptoms are that one of them is leaky. There's been lots of
discussion about this area over the years. There is also a major design
flaw in this circuit, which you will want to know about - see 'Ending
the moment of silence' on our website documents: R-390/R-390A AGC -
Ending The Moment Of Silence <https://www.r-390a.net/Wise-AGC-Mod-
Long.pdf> and R390A AGC Moment of Silence <https://www.r-390a.net/
R390A%20AGC%20Mom%20of%20Silence.pdf>.
Regards, Larry
On Sat, Nov 9, 2024 at 6:36 AM Geoff Brozny via R-390
<[email protected] <mailto:[email protected]>> wrote:
HI,
First time posting to this list, have been subscribed for a couple
months. I have not needed help with anything until now, and I am mostly
new to this. I have a R-725 that works fine except for the AGC. After
around 1 hr with the AGC in either Medium or Fast, it quits working.
Audio distorted like I set it to MGC. I seem to be able to get it to
work for what seems to be a random time by setting the AGC to slow,
then
after 10 seconds back to medium or fast.
The only issue I seem to have found is the two 1uf oil filled caps,
C546
and C547 which are parallel to create a 2uf cap. Tested while cold I
was
getting right at 2uf, hot I was getting something close to 6, so
that is
my suspected issue. Should I just replace these caps with a pair of 1uf
film caps? I do hope I can fit whatever the replacements are under the
chassis so it at least looks original from the top.
Thanks,
Geoff, KD8GRN
______________________________________________________________
R-390 mailing list
Home: http://mailman.qth.net/mailman/listinfo/r-390 <http://
mailman.qth.net/mailman/listinfo/r-390>
Help: http://mailman.qth.net/mmfaq.htm <http://mailman.qth.net/
mmfaq.htm>
Post: mailto:[email protected] <mailto:[email protected]>
This list hosted by: http://www.qsl.net <http://www.qsl.net>
Please help support this email list: http://www.qsl.net/donate.html
<http://www.qsl.net/donate.html>
______________________________________________________________
R-390 mailing list
Home: http://mailman.qth.net/mailman/listinfo/r-390
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
