A friend of mine has a Bose "wave radio" about 10 years old, and it's totally dead. Let me preface the rest of this by admitting that I have basically a high-school electronics shop education regarding electronics theory and practice. From 30 years ago.
I took the radio apart and found that the board is getting 120VAC past the on-board fuse, and the multi-tap transformer seems fine. The bridge rectifier is working.
There are two voltage regulators, a 7805 and a 7810. Neither one of them are showing any voltage at their input pins. I traced the circuit back to two transistors, 2SA1318 PNP whose respective collectors are tied to the input pins of the regulators (with a resistor).
When I measure voltage from ground to either the base or the emitter of the transistors, I get -29V on one and -15V on another. When I measure voltage from ground to the collector of the transistor(s) -- I get a reading of '0'.
So if the collector of the PNP transistor is "dead" or at zero potential compared to the board's ground -- does that mean that the transistor is bad?
I'm willing to risk the few dollars to spend on replacing these two transistors, but was wondering if I'm on the right track at least?
Thanks!
-Chris
I took the radio apart and found that the board is getting 120VAC past the on-board fuse, and the multi-tap transformer seems fine. The bridge rectifier is working.
There are two voltage regulators, a 7805 and a 7810. Neither one of them are showing any voltage at their input pins. I traced the circuit back to two transistors, 2SA1318 PNP whose respective collectors are tied to the input pins of the regulators (with a resistor).
When I measure voltage from ground to either the base or the emitter of the transistors, I get -29V on one and -15V on another. When I measure voltage from ground to the collector of the transistor(s) -- I get a reading of '0'.
So if the collector of the PNP transistor is "dead" or at zero potential compared to the board's ground -- does that mean that the transistor is bad?
I'm willing to risk the few dollars to spend on replacing these two transistors, but was wondering if I'm on the right track at least?
Thanks!
-Chris