"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 are:
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