[R-390] new member, R390A, no signal when first powered on, works after 10min but RF cutting in and out

[Larry H]

Hi Pat,  These are the tough ones.

As I was reading through all the good suggestions, I was thinking that knowing the amount of background noise (if any) you can hear when it is not working correctly can be a very good indicator of which section the problem is in.  Since it happens on all bands, you can rule out the 1st mixer and its oscillator (17 mc). If you can measure the level of internal noise when its dead, then you can when its working normally, pull out the rf amp, 2nd mixer, 3rd mixer, or disconnect some mini coax to achieve the same noise level. When you match it, the bad stage is right before that.  

Is this a 1 fuse or 3 fuse machine?  If 3, check to make sure 125 ma is the right value (just in case a cap is shorting).  You might want to use a 100 ma until you fix this problem.  Did  you change the cap in the IF that can wipe out your filters?

Good luck.  Regards, Larry


On Thursday, June 26, 2014 4:16 PM, Tisha Hayes <tisha.hayes at gmail.com> wrote:
 


It is possible that you have several problems going on at the same time.
Popping noises can also be something like a bypass cap that is
intermittently shorting out and kicking the B+ in the pants.

Usually I do not suspect something mechanical like a bad connector unless I
am manipulating the radio mechanically (tapping, twisting, pushing, etc..)
on parts of the radio that can make that intermittent electro-mechanical
problem appear or disappear. If you go chasing after the unlikely then you
are going to get frustrated and start ignoring or bypassing major portions
of what should be a methodical approach to troubleshooting.

I have had radios that I could hear the soft rush of static through the
speaker, then I would hear a "POP" and the static disappears and over the
next second or so the audio comes back to to the static sounds.. Then
3-5-10-20 seconds later another POP and the same disappearing and fade
returns.
---------------

-- 
Ms. Tisha Hayes. AA4HA

*""In this denial of the right to participate in government, not merely the
degradation of woman and the perpetuation of a great injustice happens, but
the maiming and repudiation of one-half of the moral and intellectual power
of the government of the world." -- Fredrick Douglass"*
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