Thanks for you post. My issues are with several receivers, the most recent being with my most recent acquisition which I hoped would not have so many issues. I do have some tools, VTVM, Signal Generator (but can't control output - only has Hi and Lo), ironing station and yes, Y2K R3. Thanks.
On an earlier post today, I have outlined what appears to have already been replaced and not on the latest receiver. I forgot to mention that all of the caps on the audio section had also been replaced by a previous owner. I will take to heart the suggestion to use deoxit on all of the pins and trimmers and switches in crystal deck. I will remove and test C551 in about a month when I am next back where this receiver resides. I have already done the mechanical alignment and all appears fine other than the 2 - 4 MHz sliding mechanism holding the 3 ferrite rods in the RF module stick and do not come down on their own. I thought that was why 2 - 4 MHz is totally deaf but it didn't help to move the rods to the correct level. So that will be an issue for another post when I get to it. With respect to the impedance adapter, I have purchased a little metal box, 2 BNC connectors and the correct resistors but haven't built it yet. Thanks again for your sage advice. Regards, -----Original Message----- From: [email protected] <[email protected]> On Behalf Of [email protected] Sent: Tuesday, March 12, 2024 12:30 PM To: [email protected] Subject: [R-390] RE (R390/A) AGC, etc., Haven't posted for a long time, here goes. In a general reply to Gary Biasini, you have several posts and I'm trying to find the start of your issues with a R390/A? Are these posts for the same receiver? Please list the restoration efforts at this point to help this long distance R390/A service dept. First thoughts are, these beasts are Ferrai autos, not VW's. Better tools and parts are needed. Under the list of tools: Good working VOM, Signal Generator, Tube Extenders, Tube Tester, soldering iron/station.....comes to mind. Oh yes...Y2K R3! 1st: Remove all decks from the chassis, replace paper caps. These old caps will haunt you until they are replaced. I can send you a list if needed! While the decks are removed, check connectors, resistors, switches, etc. On the RF deck are many RF transformers. They plug into the deck with pins, use Deoxit on the pins. Want more punishment? The trimmers caps have been twisted for decades and metal has transferred to the other half of the capacitor. A real small clip on the bottom holds the two sections together. Slide to one side, remove top half, clean with a Q-Tip and a very small drop of Deoxit. It works, trust me. Same with the 2nd IF section, (going by memory????). Audio deck, replace the cap that rots, check resistors, etc. Clean switches in crystal deck. Power supply usually is in better shape, but look at everything. The IF deck, replace paper caps (all of them), C551 & C553. The only replacement cap I've found for C551 is made by NTE and is a mylar cap. I forgot the impedance adapter recommended to be used for alignment, get one. It makes a difference! Going through the Y2K R3, please note the mechanical alignment sections is FIRST. If the mechanical alignment is wrong, the electronic alignment will be wrong. At this point, having crossed all T's & dotted all I's, the R390/A should be somewhat working. Now the hard part, those nasty little bugs. What isn't quite right? Checking resistance and voltages at each tube might turn up some clues. Using a sig/gen to inject a signal, following said signal with tube extenders and an o'scope is one method. This is fun once you have a R390/A that is 100%! You mentioned a possible AGC issue. Long ago I chased an AGC issue and replaced all those ceramic capacitors, about 2 dozen. Ouch! By memory, I'm older than dirt, they all are 5000pF +- 15% 1000VDC all along the AGC line. AGC issues and replacing mechanical filter are a pain in the backside, been there. Regards, Craig ______________________________________________________________ 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
