Pull all the tubes one at a time and then put them in a tube straightener if you have one or hit the pins with a bit of DeOxit. Then loosen and tighten again, as was, ALL of the ground tie points and all of the shield and IF can mounts.. There is a dissimilar metals corrosion issue related to differential metal surface potentials that Collins, or no one, understood at that time and just sitting together builds a corrosion product that winds up semi, or completely, insulating the connection..
Then go to the bottom of the rig and carefully remove one at a time all of the injection oscillator crystals and deoxit the pins and reinsert them in the correct socket. BE careful not to shock the crystals.
Now, take a plastic tooth pick and put a VERY small amount of deoxit on the band, function switches contacts BUT NOT THE WAFER. Then exercise the band, function etc switches and let the whole thing sit for about 2 hours to let the deoxit dry. This is a good time to reform the PS electrolytics if you have time and the mil-spec and the equipment.
Now, plug her back in and add a speaker and with the antenna open, turn on the radio and then, when warmed up, turn on the calibrator (You should have pulled, wiggled and replaced this also) and make sure you can see the calibrator on all bands. By see, I mean you get a S-Meter indication. If a band shows S-Meter action in the AM detect mode, this confirms the front end of the receiver thru to the AGC detector point in the IF. Log any missing bands. Now switch to CW mode and look again at the calibrator with the audio turned up and this should, of course ,give you a tone in the audio out if the IF thru the detector/audio amp is working. Log any discrepancies.
After that, let's talk. I think you will like the radio better after this basic wakeup call.
Bill Carns, N7OTQ K0CXX, Trustee MRCCC Editor Signal Magazine CCA Board Member CCA # 94-00009 Wimberley, Texas 512 847 7010--- Original Message ----- From: "CHARLES RAKES" <charlesrakes@xxxxxxxxxxxx>
To: <collins@xxxxxxxxxxxxx>
Sent: Tuesday, March 17, 2009 7:45 AM
Subject: {Collins} 75A-4 What to do?
A few days ago I asked here about my 75A-4 needing L7 and its trimmer capacitor. When I first turned the receiver on I did not receive any signals....wiggled V14 and V15 and was able to receive on both 80 and20meters....of course nothing on 40. Then I took the bottom of and it looked clean, however I could no longer get it to receive. The receiver is in verynice condition other than the problems I've just mentioned. It has threefilters and the spinner knob. The cabinet and front pannel are also in verygood condition.....I do not want to part out such a nice radio and am not sure I will be able to bring it back...sold my good generator and tubechecker several years ago and I'm not as steady as I once was. ha Should Itry selling as is? What would you do? Thanks, Charles _______________________________________________ CCA DAYTON 2009 INFORMATION: HOTEL - BANQUET - BOOTH http://tinyurl.com/dlyywg SHARE THE FUN: JOIN THE COLLINS COLLECTORS ASSOCIATION TODAY ! http://www.collinsradio.org/membership/ -paypal accepted- NETS: Tues & Thur: 3.805 MHz-2000 Central + Fri: 3.895 MHz-2000 Pacific SUNDAYS: 14.263 MHz-2000 UTC + AM Net: 29.050 MHz-1200 Central 1st Wednesday AM Net 3.880 MHz-2000 local (ET, CT, MT, PT)