Sony STR-6045 FM trouble
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| Posted on August 25, 2015 at 08:28:04 | ||
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Posts: 411
Joined: March 29, 2009 |
I inherited my grandfather's Sony STR-6045 receiver ~1971, and my late brother apparently started to repair it, but gave up. I replaced the shorted output transistors in one channel and got it working . . . I thought . . . until I tried the FM tuner section. Signal strength is very good and consistent, but the sound crackles and cuts in and out. The overall audio signal level seems to be low. I think I've narrowed it down to the transistor 2SC710 (Q206) that drives the ratio detector, but I've had to order that transistor. I'm hoping it's not the small discriminator transformer that this transistor drives. The emitter voltage of this transistor fluctuates with the crackling, and placing a scope probe on the collector silences the crackling along with the rest of the signal. The transistor tests OK via a diode test, but I suppose it's possible that it fails under applied voltage. For anyone who's worked on a Sony receiver of this vintage, do the transistors seem to be the main things to fail? Many of the solder joints on the radio receiver PCB have barely any solder on them, but I couldn't fix this problem by resoldering questionable joints. Also, if any resistors need to be replaced, are Vishay/Dale metal films acceptable in the IF section to bias the transistors? The manual describes the resistors in it as "carbon type," but doesn't say if they're carbon comp or carbon film. They look sort of like carbon film, but I'm not as familiar with Japanese components as I am with American or European.
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