i have an 80s Toshiba Bombeat SX-28 boombox, it uses a TDA1515BQ amp. there's a rather annoying hum on the left channel but not on the right one, and it doesn't seem to change at all in volume with the volume knob or disappear if i mute the left channel with the balance knob 1/2
there's no visible damage anywhere, no leaky or blown caps, no broken traces or cold solder joints. does anyone have any experience with audio amps of this vintage to give me a hand on where to start troubleshooting the hum? 2/2
so i think i found the issue.. there's a bodge wire i thought could be factory but on second inspection isn't, it's bypassing output of the bridge rectifier into the emitter of a transistor, i'm not sure why, but once i removed it the hum was gone... along with the FM circuitry
looks like the transistor it was tapping into might be dead and the bodge was there to keep power going through the board? it's a BC337, i don't have any equivalents.. i found some BC548s in my parts box but they're rated for lower current than the 337
so now i need to figure out why that bodge wire is there and how to fix the original issue without introducing hum