[R-390] R-390A IF deck caps in T501 or T502

[Roger Ruszkowski]

Barry, In youth mil spec caps did not suffer infant mortality.Digital and all in circuit measurement of capacitance values is still a tough troubleshooting procedure.Do use what you have to your best advantage. Dave, Before surgery do A mechanical loosen and retighten  on all the ground lug hardware.Check for change. Now that you know what's where in there.Run a soldering iron through the solder joints.Check for change.Now you may wish you had a good capacitance meter. Oxide in the lug joints are current most often encountered.A cold solder joint that has finally gone up in resistance has second place.All things said the caps are not problematic.As Larry will attest to the critters do fail. Mole did not have a boat anchor and thus thought the boat on the pond was wonderment enough. Think of pondering an IF deck on the bench as a reach into craftsmanship.Those parts want to be looked at and touched.Some inspection and reflection time will bring the spirit around to wanting to effect a repair if needed and best adjustment.The vacuum pulls you in. You have a one off 50 year old five dimension puzzle in the room waiting to be solved and you are saving it because you are afraid to have so much fun in the bench top quest.You are not the first person who has worked on your receiver. Get free and enjoy the repair time.    Larry,Good job well done and the 2404 is accepted as submitted. Roger  -----Original Message-----
From: Barry <n4buq at knology.net>
To: Larry H <larry41gm at gmail.com>
Cc: R-390 Forum <r-390 at mailman.qth.net>
Sent: Wed, Jan 23, 2019 5:39 pm
Subject: Re: [R-390] R-390A IF deck caps in T501 or T502

That's a logical assumption and good fix (and I presume Roger R. would say they didn't rely on cap checkers either...).

Thanks,
Barry - N4BUQ

----- Original Message -----
> From: "Larry H" <larry41gm at gmail.com>
> To: "R-390 Forum" <r-390 at mailman.qth.net>
> Sent: Wednesday, January 23, 2019 4:22:45 PM
> Subject: Re: [R-390] R-390A IF deck caps in T501 or T502
> 
> Dave, it was more of a process of elimination.  After determining that the
> 2nd stage gain was erratic, I started with the tube, then the bypass caps.
> Then the voltages on the tube.  Then the output transformer, so I checked
> to see if the 2 slugs were still at their peak.  One was and the other not,
> and it would not peak.  I measured the coil resistance and examined it for
> damage and loose wires.  All ok there, so it had to be the caps.  Since I
> don't have a cap checker, I removed both.  This is one time I wish I had an
> accurate cap checker, then I would have checked the mica first.  Replacing
> both confirmed one of them was bad.  Reinstalling the ceramic with a new
> 200 pf mica confirmed it was the mica.
> 
> Regards, Larry
>