Hi everyone,
I got an old Wega V-3840-2 audio amplifier from my dad a few years ago. Worked like a charm, up until a few weeks ago. I noticed that it got quite warm, but suspecting it was the sun, I just shut it off for a while and it resumed working. Then, suddenly, the right audio channel developed a nasty hum (I think about 100 Hz, which corresponds to twice the mains frequency here). I immediately shut it off, and only after a while turned it on, and it worked again. However, the very next week it started to hum again, and this humming would suddenly end with a 'pop', before starting again. The input audio completely cuts out while the hum is there.
After opening it up, I noticed the rightmost main amp transistor (an A671 PNP) heated up significantly. So, I checked around there for possible dry solder joints, re-soldered some just to be sure, but to no avail. I replaced the A671 and it's NPN complement (the C1061) with modern equivalents (according to the local hardware store), the BD243 and BD244. However, before doing that, I checked which side I should replace just to be sure, but I already disconnected the load (the speaker). This, I think, blew a small diode (with a nice puff of magic smoke) that was stuck against the C1061 transistor (perhaps a thermal protection diode?). The result is that it's still humming, but now it will do so continuously (no ending with a 'pop').
What would be a good next step for troubleshooting? Could I try temporarily remove or rather short the diode? Since it's embedded in epoxy, I can't really see what kind of diode should be used as a replacement. Additional info: the main amp board is made by Sony, and seems to have the type number S 47, or something starting with 1 584.
I got an old Wega V-3840-2 audio amplifier from my dad a few years ago. Worked like a charm, up until a few weeks ago. I noticed that it got quite warm, but suspecting it was the sun, I just shut it off for a while and it resumed working. Then, suddenly, the right audio channel developed a nasty hum (I think about 100 Hz, which corresponds to twice the mains frequency here). I immediately shut it off, and only after a while turned it on, and it worked again. However, the very next week it started to hum again, and this humming would suddenly end with a 'pop', before starting again. The input audio completely cuts out while the hum is there.
After opening it up, I noticed the rightmost main amp transistor (an A671 PNP) heated up significantly. So, I checked around there for possible dry solder joints, re-soldered some just to be sure, but to no avail. I replaced the A671 and it's NPN complement (the C1061) with modern equivalents (according to the local hardware store), the BD243 and BD244. However, before doing that, I checked which side I should replace just to be sure, but I already disconnected the load (the speaker). This, I think, blew a small diode (with a nice puff of magic smoke) that was stuck against the C1061 transistor (perhaps a thermal protection diode?). The result is that it's still humming, but now it will do so continuously (no ending with a 'pop').
What would be a good next step for troubleshooting? Could I try temporarily remove or rather short the diode? Since it's embedded in epoxy, I can't really see what kind of diode should be used as a replacement. Additional info: the main amp board is made by Sony, and seems to have the type number S 47, or something starting with 1 584.
