mauser
New Member
Hello all, I am new at troubleshooting electronics, and am hoping for some help and direction from those more knowledgeable than myself.
I was given this vintage Sherwood with a sound output problem, this is what I know so far:
Visual inspection shows nothing significant of concern, some dust accumulation much of which I swept out with a soft brush, but nothing swollen, darkened, or leaking that I can see. The solder joints that are visible all appear intact and the boards appear to be in good condition.
I did not remove the bottom of the unit, and there seems to be a fair amount going on in the lower half, including all of the controls except the pot and the tuner knob.
The unit powers on and lights up with no appreciable hum or other noise (without speakers attached)
The "protection" light is on most of the time.
There is no sound from the speakers, except when at rare moments, the protection light goes off and the speakers produce sound for a few seconds, not sure if it is only one channel or both channels.
When headphones are plugged in, there is sound only on the left channel.
If headphones are plugged into the tape-out port on the lower left front panel, sound works fine on both channels.
I tested all eight transistors in the back (4 pairs of alternating 2SD427 and 2SD557 I believe), and two of them register at zero so assuming they are dead (a pair of the 427s). The dead transistors are the second pair from the left when looking at the unit from the front.
I could buy replacement transistors, but not sure if they failed due to a short somewhere else in the system, or if it was a thermal failure of some kind? There seems to be some sort of thermal conductive grease underneath the plastic gaskets that they mount on. They are mounted inside of what appears to be a large aluminum heat sink.
That is everything I know so far, what would you recommend I do next? Appreciate the input and help.
I was given this vintage Sherwood with a sound output problem, this is what I know so far:
Visual inspection shows nothing significant of concern, some dust accumulation much of which I swept out with a soft brush, but nothing swollen, darkened, or leaking that I can see. The solder joints that are visible all appear intact and the boards appear to be in good condition.
I did not remove the bottom of the unit, and there seems to be a fair amount going on in the lower half, including all of the controls except the pot and the tuner knob.
The unit powers on and lights up with no appreciable hum or other noise (without speakers attached)
The "protection" light is on most of the time.
There is no sound from the speakers, except when at rare moments, the protection light goes off and the speakers produce sound for a few seconds, not sure if it is only one channel or both channels.
When headphones are plugged in, there is sound only on the left channel.
If headphones are plugged into the tape-out port on the lower left front panel, sound works fine on both channels.
I tested all eight transistors in the back (4 pairs of alternating 2SD427 and 2SD557 I believe), and two of them register at zero so assuming they are dead (a pair of the 427s). The dead transistors are the second pair from the left when looking at the unit from the front.
I could buy replacement transistors, but not sure if they failed due to a short somewhere else in the system, or if it was a thermal failure of some kind? There seems to be some sort of thermal conductive grease underneath the plastic gaskets that they mount on. They are mounted inside of what appears to be a large aluminum heat sink.
That is everything I know so far, what would you recommend I do next? Appreciate the input and help.
