"Dave" bravely wrote to "All" (22 Jun 05 05:18:25)
--- on the heady topic of "Probably simple AM radio repair"

Da Subject: Probably simple AM radio repair
Da Xref: aeinews sci.electronics.repair:51188

Da Hi,

Da I acquired a Tandy Chronomatic 246 clock radio that is in great
Da condition. The only problem I have is AM reception below 900 kHz is
Da almost non- existant. I can turn up the volume to max and touch the
Da internal antenna to hear stations at low volume. The FM band works
Da great.
Da I did replace a leaking 4.7u electrolytic cap that was nearest to the
Da adjustable yellow choke and tuning cap, but it made no difference. I
Da also adjusted the chokes a little to see if I could get better
Da reception near 900 kHz, but no luck.

Da I'm suspecting there might be a broken wire in the internal AM
Da antenna? The wires in position on the antenna a

Da Red-Black-Blue White

Da If I touch the white wire, much better reception. But it is soldered
Da to the PCB securly.

Da Is there a way to test the antenna, like ohm it out? Any other ideas?

Da Thanks,


Dave,

The loopstick antenna can often be optimized by moving the pickup coil
along the length of the ferrite rod. However, I don't think this is
the real problem. There might be a break in the tuning capacitor or
its trimmer. Perhaps the rf xformer/mixer cans has an open coil.
Perhaps the local oscillator/mixer (transistor, IC) is stalling below
900KHz. This might be the supply bypassing electro for that circuit
being open, try tag soldering a good one across it. It should be
obvious where the problem lies by signal tracing with a scope or
demodulator probe. Was this an existing problem or a sudden event?

A*s*i*m*o*v

.... That was a fascinating period of time for electronics