12-06-2022, 05:53 PM
(This post was last modified: 12-06-2022, 05:53 PM by Mike Watterson.)
Great!
Well, the FM only uses the chip for IF. Likely the VHF LO coil got moved/bashed a bit, maybe RF coils too. You can't connect direct, but the LO does leak out the aerial in, so you can use a 76 MHz to 120 MHz set to sniff LO. Likely 10.7 IF though 6.5MHz has been used. Possibly LO is 10.7 below RF so might be 76.8 to 97.3 for 87.5 to 108. If so tube the DUT to 100 MHz and a 2nd working set should get a signal at 89.3. A set with tuning meter, or put DVM on discrimator helps. Tune around on test radio to find LO from your faulty set.
Compressing LO coil lowers frequency.
Obviously a spectrum analyser makes it easy. The transistor nearer aerial will be buffer/preamp and 2nd transistor is LO, feeding an IFT feeding IC.
Well, the FM only uses the chip for IF. Likely the VHF LO coil got moved/bashed a bit, maybe RF coils too. You can't connect direct, but the LO does leak out the aerial in, so you can use a 76 MHz to 120 MHz set to sniff LO. Likely 10.7 IF though 6.5MHz has been used. Possibly LO is 10.7 below RF so might be 76.8 to 97.3 for 87.5 to 108. If so tube the DUT to 100 MHz and a 2nd working set should get a signal at 89.3. A set with tuning meter, or put DVM on discrimator helps. Tune around on test radio to find LO from your faulty set.
Compressing LO coil lowers frequency.
Obviously a spectrum analyser makes it easy. The transistor nearer aerial will be buffer/preamp and 2nd transistor is LO, feeding an IFT feeding IC.
