Title: R-390A Alignment Post by: W7SOE on March 15, 2008, 02:05:51 PM Working my way through the RF alignment and ran into a bad trimmer cap in an RF can. These caps seem to be integral to the assembly. Is there a way to replace them? Are they available?
Also, some of the antenna transformer slugs are peaking VERY low, is this indicative of a bad mica cap? Thanks Rich Title: Re: R-390A Alignment Post by: w3jn on March 15, 2008, 03:34:28 PM If there isn't a nice sharp peak (with the exception of the antenna coils) you have a bad S/M cap or a bad trimmer.
I've never had to replace a trimmer in these and it's been years since I've had a can apart so I can't give you any advice there. I have a 390A on the bench right now that'll peak at the bottom of the 16-32 MHz band fine but won't track up top. I suspect it might be one of the S/M coupling caps so I'm gonna hafta pull the RF deck after I verify it isn't the bandswitch gone outta sync. Title: Re: R-390A Alignment Post by: WA1GFZ on March 15, 2008, 03:38:45 PM John, make sure the slug is ok and not missing a hunk of metal.
Title: Re: R-390A Alignment Post by: WV Hoopie on March 15, 2008, 04:28:19 PM Rich,
The trimmers should give two peaks, either peak will work. A peak with the slug low in the holder is a sign one or more of the silver mica caps are bad. The silver has migrated through. Mouser or Newark has them and I've replace several in my R-390/A's. The trimmers can be disassembled by sliding the retainer to one side. The top section that turns will have some silver material which has been transfered onto the bottom surface. A q-tip with some De-Oxit will remove the plating that has rubbed/scrapped onto it. The epay place has em for auction every so often. 73's wd8kdg Craig Title: Re: R-390A Alignment Post by: W7SOE on March 17, 2008, 03:17:52 PM The trimmers can be disassembled by sliding the retainer to one side. The top section that turns will have some silver material which has been transfered onto the bottom surface. A q-tip with some De-Oxit will remove the plating that has rubbed/scrapped onto it. Indeed, I was able to bring three dead rf cans back to life by disassembling and cleaning the trimmers. On one of them I broke the coil wire so it lost a couple turns when I fixed it. It aligned fine though. Thanks for the good advice, the alignment is done! Rich |