Fleetwood 2002 - SW works, hum & no reception on AM.

[VintagePC]

I have a fleetwood model 2002 SW/AM/Phono radio which is almost functional. I get a loud hum (it does change when I adjust the dial) when on AM and can't find any stations... but shortwave works with no hum at all.

The schematic is here:
http://vintagepc.site50.net/site/fle.../RADIO_006.png

The way it's wired up, it looks like if SW is working, then it means the tubes are functional.. I have checked basic stuff like continuity but I'm not above checking it again if someone thinks there might be an open coil or so somewhere.

Have not tried an alignment yet; but I'm unsure whether that's the culprit or not; there aren't any caps in the broadcast section that were paper; all those I've changed are shared between the two.

Hopefully someone here can help me with this, it's got me stumped but is probably something the more intimate of the radio techs here can diagnose by smell or something

[DavGoodlin]

Thats a nice and easy to understand receiver.
I would look at the band selector switch, L4 and L2 in that order.
Just see if there is continuity through each

[VintagePC]

Originally Posted by DavGoodlin

Thats a nice and easy to understand receiver.
I would look at the band selector switch, L4 and L2 in that order.
Just see if there is continuity through each

Aye, will verify tonight and report findings. I noticed yesterday while working on it that the hum got louder as I moved my hand closer to one of the wires... Perhaps a poorly connected ground or something is picking up 60hz and throwing off the oscillator. Thought I cracked it earlier when I had continuity to ground on the antenna side of a trimmer cap but it was that way by design.

[old_coot88]

Assuming you've cleaned the bandswitch with 'Deoxit' or similar cleaner, look the the rotor wafers carefully while you rotate the switch. Be sure they are secure on the shaft and not slipping.

This condition occurs occasionally in wafer type TV tuners. One rotor can be slipping on the shaft or not turning at all.

[VintagePC]

As best I can tell, the bandswitch is making proper contact and the coils aren't open circuit.

Could a bad C8 (as in zero capacitance) cause this? it's the only non-shared cap limited to the broadcast section, and appears to be a mica domino-style cap.

I re-verified shortwave is indeed working as I seem to be picking up Radio Havana at around 17 Mhz, and a few other stations for which I didn't hear a call sign.

If it's unlikely to be C8 I'll have to set it aside until I get a signal generator I can tune to an AM frequency and trace through to see where the signal is dying.

[electroking]

Remember the basic trick: make sure the local oscillator is running by listening
for it on a portable radio. The LO should be 455 kHZ above the tuned frequency,
that is 995 kHz when set to 540, and 2055 kHz when set to 1600. Of course an
AM radio will let you check the bottom of the band only, but that should be enough.
Good luck!

[VintagePC]

Originally Posted by electroking

Remember the basic trick: make sure the local oscillator is running by listening
for it on a portable radio. The LO should be 455 kHZ above the tuned frequency,
that is 995 kHz when set to 540, and 2055 kHz when set to 1600. Of course an
AM radio will let you check the bottom of the band only, but that should be enough.
Good luck!

Was just thinking of that but was avoiding it because I don't have an AM radio on hand... though I can probably snatch one from somewhere... so even if shortwave works is no guarantee the LO is working... and let me guess, if it isn't running for BC, it's a weak tube, but if it is running and just off-frequency, it's likely a circuit problem?

[electroking]

The LO may be working OK on SW because all the capacitors and coils are correctly
connected, but may fail on the BC band because of a problem with the coils for that
band. A 6BE6 that does oscillate on the SW band is most likely fine for BC. Good
luck!

[VintagePC]

Well, that was interesting. Seems like I don't have a problem at all, I'm just in a very noisy area with zero AM reception.

I can locate and hear the LO go up and down the dial on the other AM radio, and it also has a _very_ loud hum at no station. Also found an area on the dial where I'd receive a loud thup-thup-thup noise on both radios, and heard it echoed when I set the console to that channel and tuned the other one to the LO.

*facepalm* Whelp, time to locate a dial lamp and pop the radio chassis back in the cabinet, I guess Looks to be a type 51 judging by the "E51" stamped on the base.

You live, you learn. Onwards to the TV part now!

[VintagePC]

Just like to post an update on this - I shotgunned all the resistors today since I ordered up a batch anyway. The nasty hum in the AM band is gone (despite the resistors checking ok - probably had one that drifted as it got hot), and I get some stations, though they're really noisy. Probably because I'm using a really short wire, but if it doesn't improve it may need an alignment. Either way, problem resolved!