Hi all, I've got an older Sony 2 channel receiver that I'd like to keep going, as it sounds great, and we don't need more than two channels anyway. Picked this unit up for cheap second hand a while back, and it worked well for a while before it started acting up.
I've narrowed it down to one of the amp(pre-amp?)transistors, but seeing as I'm fairly noobish still when it comes to troubleshooting electronics, I wanted to run it by anyone familiar with amp circuits, and see if anyone had any input as to what exactly might have caused the failure.
Symptoms:
Unit goes into protect mode if left on overnight. Cycling power clears protect mode. Left channel is a clipped static sound. I.E. only the high volume parts of the sound come through as a sort of static.
Troubleshooting and elimination:
Eliminated the main amp transistors via testing and swapping them. Worked when reassembled, so thought perhaps it was a bad solder joint. Failed again within a day or so, same channel.
Took a closer look at the board, and found a couple dark areas and what seemed to be visibly failing solder joints. Re-soldered joints, same problem.
I then started pulling and testing the transistors in this darkened patch, and finding no faults I swapped channels when re-installing them. Bingo! The problem switched channels. It would seem it is one of the 2SC2958 transistors.
The 2sc2958 and 2sa1221 pairs get very hot to the touch.(Hard to touch them for more than a couple seconds, and when I put an alligator clip on one it got warm). Hot enough to brown the board, and also cause at least partial failure of the solder joints. The 2sc2958 on the left channel seems to be the failing component. The left channel also has a darker 'burnt' area from the heat than the right.
Questions:
1)Is it likely that they've been getting this hot for the life of the unit, and it's just now failing from the effects of the heat? Or is another component failing causing the transistors to overheat? (These are getting hot to the touch without any input or output happening. No speakers hooked up. No inputs. Just sitting there turned on.
2)Which other components are the likely candidates for causing this problem, if any?
3)The small arrows with numbers on the schematic are indicating voltages, correct? How far off is acceptable variation? (I've seen 1 volt maybe a bit more variations from what's printed on the page).
Any help you can be would be great. I hope this is acceptable to post here. If there's a better forum for this, please let me know. Seems like a good project to learn some things on. It's fairly simple being 2 channel, it's easy to pop open and work on without much dis-assembly, and it puts out some pretty good sound. I figured I'd try to learn a bit more, and save some money at the same time. I've got the time to troubleshoot it.
Thanks!
(click to enlarge - pics embedded via imgur - let me know if they're not visible)
I've narrowed it down to one of the amp(pre-amp?)transistors, but seeing as I'm fairly noobish still when it comes to troubleshooting electronics, I wanted to run it by anyone familiar with amp circuits, and see if anyone had any input as to what exactly might have caused the failure.
Symptoms:
Unit goes into protect mode if left on overnight. Cycling power clears protect mode. Left channel is a clipped static sound. I.E. only the high volume parts of the sound come through as a sort of static.
Troubleshooting and elimination:
Eliminated the main amp transistors via testing and swapping them. Worked when reassembled, so thought perhaps it was a bad solder joint. Failed again within a day or so, same channel.
Took a closer look at the board, and found a couple dark areas and what seemed to be visibly failing solder joints. Re-soldered joints, same problem.
I then started pulling and testing the transistors in this darkened patch, and finding no faults I swapped channels when re-installing them. Bingo! The problem switched channels. It would seem it is one of the 2SC2958 transistors.
The 2sc2958 and 2sa1221 pairs get very hot to the touch.(Hard to touch them for more than a couple seconds, and when I put an alligator clip on one it got warm). Hot enough to brown the board, and also cause at least partial failure of the solder joints. The 2sc2958 on the left channel seems to be the failing component. The left channel also has a darker 'burnt' area from the heat than the right.
Questions:
1)Is it likely that they've been getting this hot for the life of the unit, and it's just now failing from the effects of the heat? Or is another component failing causing the transistors to overheat? (These are getting hot to the touch without any input or output happening. No speakers hooked up. No inputs. Just sitting there turned on.
2)Which other components are the likely candidates for causing this problem, if any?
3)The small arrows with numbers on the schematic are indicating voltages, correct? How far off is acceptable variation? (I've seen 1 volt maybe a bit more variations from what's printed on the page).
Any help you can be would be great. I hope this is acceptable to post here. If there's a better forum for this, please let me know. Seems like a good project to learn some things on. It's fairly simple being 2 channel, it's easy to pop open and work on without much dis-assembly, and it puts out some pretty good sound. I figured I'd try to learn a bit more, and save some money at the same time. I've got the time to troubleshoot it.
Thanks!
(click to enlarge - pics embedded via imgur - let me know if they're not visible)



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