Hi Jordan,
It looks like I may have enough space under the original caps to mount a
terminal strip on one of the mounts for the original cap, and I may be
able to fit a pair of 1uf 400V film caps. I do not have any on hand,
only 600v ones, and they are too fat to fit in there. I have never tried
to open one of the caps before to re stuff them, so I am a bit hesitant
to make this my first try..
thanks,
Geoff
On 11/9/2024 10:13 AM, Jordan Arndt wrote:
I've replaced C551 with 1.5uF film caps in the 3 390A IF decks in my
radios...
It's not an elaborate solution to the 'moment of silence' issue, but the
recovery time is much much faster than the original 2uF caps produced...
I took C551 apart and inserted the film caps inside the original
assembly, although that might not be possible in the R-390/R725 IF decks.
my .02 cents worth....73...Jordan VE6ZT
----- Original Message ----- From: "Larry Haney" <[email protected]>
To: "Geoff Brozny" <[email protected]>
Cc: <[email protected]>
Sent: Saturday, November 09, 2024 8:03 AM
Subject: Re: [R-390] R-725 AGC quits working after 1 hr.
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]>
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
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
______________________________________________________________
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
______________________________________________________________
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
