Here are a simplified diagram and the complete one as screenshot from kicad: (maybe to minimize pop-sound from the caps charging?) The 2SB1241 switches the +15VDC comming from the external supply to the internal power rail when the switching inverter provides the -15VDC. I reversed the power circuitry so you know the usecase. I'm not sure which other parameters should be considered, like some parameter that depends on the voltage on the base between the resistor divider and the zener maybe. parts like BD240 with hfe below 100 are probably not usable.EEVBlog: RE: Common / generic / cheap / easy to find parts - TIP33 overkill current, too low hfe.EEVBlog: Common / generic / cheap / easy to find parts - TIP34x (power PNP, 10A, 40-100V) also a bit overkill.lists D45H Series, a bit overkill with 10A collector current.PNP B772 Transistor replacement - BD140 is a popular PNP, can handle even a bit more power, hfe is a bit different.Determining Suitable Replacement Transistor?- "high current, high gain/high beta".What i could gather from similar questions/other sources:
The original package is 3-SIP, but there are no big space constraints, a TO-126 or even a TO-220 would fit for example. I believe the high hfe, 1A collector current and 1W power dissipation should not be lower for a replacement, but i'm not sure on other parameters. The original is discontinued and shops like Digikey, Mouser or TME don't have it in stock anymore. The 2SB1241 is a bit hard to read now, but i'm very sure it's the current gain option R with hfe 180-390. I haven't found any other problems in the circuitry yet, i think only this transitor is faulty. The Marking of the transistor is B1241 but due to the 3-SIP package im pretty sure its a 2SB1241. I have a Peavey PV8 USB Mixing console which doesn't turn on anymore, the problem is a burned PNP switching the +15V rail.
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