No manual tuning, only presets 40-180 - Printable Version
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+--- Thread: No manual tuning, only presets 40-180 (/showthread.php?tid=15516)
No manual tuning, only presets 40-180 - tvmicrowave2002 - 10-12-2016
Hi everyone. I'm hoping someone can shed some light on an issue that I am having.
I just completed the restore of the 40-180. Thanks to the help of a user, I was able to get the tracking working perfectly. However, I noticed an issue where when peak tuning on a stronger station, when I shifted slightly off dial (maybe +/- 2 kHz) I would hear a second peak. I thought maybe the IF needed to be peaked a little tighter. I connected the generator using a .1 filter cap to the antenna input at terminal 1 and peaked the IF referencing the DC of the 1232 pin 6. Once I got a little more out of it, I connected the antenna back to terminal 1 so I could check RF tuning. That's when the dial fell silent. Presets work fine, but when switched to dial, it performs like the antenna isn't connected. You have to crank the volume to hear the noise floor and WGN (local) is the only station I can pickup faintly. However, call up WGN and other presets and it will blast you out of the room.
I experienced this about a week before when I first tried an alignment. The procedure was similar except in that case, I directly connected the generator to the antenna input, heard a slight 'pop' in the audio, and the dial noise fell off just like now. At that time, I did not have any presets configured so I do not know the preset performance at that time. It was late in the night and I thought I blew something and thought I would pick it up the next day. However, the next morning, everything was fine and I continued the alignment.
I've checked the switch action for dial and the other 7 presets and it measures OK. Both sides of the switch appear to be fine on all except preset 2. The bottom side (not exposed) pin is bent on preset 2 and I'm not sure I can repair it. Here's what's interesting. When on shortwave and sending 18 MHz from the generator, I can hear my tone, but it is much softer than normal. However, when I put my finger at the top of the 6J8G OSC/MIXER tube, it blasts back to normal. Doing this same finger test on AM does nothing. Cap 19 and 19a and 21B were tuned properly before on my first alignment and I have not moved them in fear of really falling off track. I don't want to move them until I get this issue solved.
Any ideas? Possibly a bad 6J8G tube? Even possibly a shorted 2 gang compensator? Everything logical points to a switch contact on the dial button but I am fairly certain it is good. It measures good and I cleaned it using contact cleaner for good measure.
I hope you guys can figure this out. My fiancé is putting pressure on me to cleanup my living room mess..
-Kyle
RE: No manual tuning, only presets 40-180 - Radioroslyn - 10-12-2016
So does tune manually on SW???
RE: No manual tuning, only presets 40-180 - tvmicrowave2002 - 10-12-2016
I wouldn't say for sure that it tunes, it's just when I insert 18 MHz from the generator, I can hear it, although it is softer than expected. When I put my finger on the tip of the 6J8G tube, it is strong, as if the unit is functioning properly. I did not track the SW dial to verify performance, only at 18 MHz.
When I perform this same test on AM at 1400 kHz and 580 kHz, I get nothing. No faint audio, and the finger at the tip of the 6J8G does not make any difference.
IF at 455 works as expected. Presets are all strong as if the tuner is functioning properly.
RE: No manual tuning, only presets 40-180 - Radioroslyn - 10-12-2016
If you can get it to operate on SW then your tuning cap isn't the issue. I'm thinking that 18mc is at the high end of the SW band. How about in the middle or low end? There is more of a possibility for the plates to be shorting. Typically if the 6J8 mixer is going to be a problem it will be at higher frequencies, like on SW verses the BCB.
RE: No manual tuning, only presets 40-180 - tvmicrowave2002 - 10-18-2016
I figured this out last night. When I was restoring the chassis, I cleaned the tuning condenser in white vinegar and then baking soda and water. I used 0000 steel wool to clean off the rust after the vinegar bath. I could see a few metal burrs from the steel wool in the RF gang that was causing a short. They were very small. I was able to blow them out with a spray can. Back to normal now. This one took some time and I got aquanted with deoxit in the process while attempting to fix the issue bu cleaning the preset switch assy.
Thanks again for your input, Terry.
RE: No manual tuning, only presets 40-180 - Radioroslyn - 10-18-2016
Your welcome!
Steel wool is not a great idea, if you need an abrasive scotch bright is a good one.