[sparkin' chassis]

radio had limited reception only w/external ant. Changed paper and electrolytic caps. Now only works w/pushbutton presets, no manual tuning.Then even stops getting anything w/pushbuttons after 2-3min.warmup.

[Radioroslyn]

Sounds like it's time to clean the pb assy.
Terry

[Electrothaumaturgist]

Yes, cleaning the push button contacts is a great idea. However, when I got the 42-400 first running, I could only manually tune it in- no push button action. So, I played with it awhile, and found the oscillator coil had a bad (loose) wire going into the center of that coil. (The wire was frayed going over the top of that coil, and only one strand of the outside wire was making contact with the center wire). I was able to drip one small drop of solder on it and "catch" that single fine wire in the center from the lead. Can't hurt to check that coil. (Be extremely careful when checking that, though-very delicate). Also, check that all your tubes are lit- jiggle the xxl and xxfm tubes and and wait a few seconds to see if that helps. (Sometimes the contacts at the tube bases are dirty). Good luck.

[sparkin' chassis]

I cleaned the tube sockets and disassembled the push button assembly and cleaned the contacts. now the presets work but still no manual tuning.

[Electrothaumaturgist]

That is the way it kind of was going for me for a brief amount of time. Sometimes it would only tune in stations with the pushbuttons, next time it would only work by manually tuning it. What it boiled down to was DEFINATELY that oscillator coil (for me anyway). The stranded wires went over the top of the coil form (quite tightly) and was attached to that single hair wire in the center of the form. When I touched it with my insulated prod, it bridged the gap and functioned normally. Fixed it as stated earlier. Hopefully your fix will be as easy as mine was. Luck be with you!

[sparkin' chassis]

Checked oscillator coil tests good. when connected to an external antenna there is an area around 600 on the am dial that receives static with the volume turned all the way up.