MyLastWord
Active Member
I bought this dead (no sound for both channels) SX-680 receiver for cheap to revive it.
The first order of business is to blow away all the dirt, then clean all the knobs, switches and the connections at the back with electronic contact cleaner.
Follow the service manual, I then replaced the transistors as follow.
- 2SA725s/2SA726s with KSA992
- 2SC1919s with KSC1845,
- 2SC1438 with KSC1845,
- 2SC1384 with KSC2690
- 2SD712 with KSC2073.
Next I replaced all electrolytic caps except the 2 big 8000uF/42V ( I don't have any handy).
One thing I learn during this exercise that replace the 220uF/63v with 390uF/63v (also don't have any 220uF/63v handy) will cause loud hums, so I put back the original 200uF/63V.
Searching for issues with SX-680 from this site, I replaced resistors R401 (33ohm) and R410 (100ohm) and replacing the Diodes D401/D402 10E2 with 1N4004 for good measure.
Once all of this is done. I start it up everything came up (except few light bulbs). Test few AM/FM channels all goods. Test Aux also good. All goods except 2 issues: 1) Only Left channels is working and 2) minor hums (audible when not play anything)
So I would think the right power pack STK-0039 would be dead. To test this, I swapped around the STK-0039.
Nothing changed, still minor hums, left channels still worked and no right channels. What!?!?
Measuring the voltage of the 2 STK-0039 , and they all seem within expected specs.
I also did try to replace the pair of 2SA798 with DIY combining 2 KSA992s and replacing the 2SK117 with 2SK30A nothing changed still so I ended up put them back.
At least, I and half way there (1channel to fix). I am running out of ideas, what to check and replace next and looking for help from collected wisdom/experiences here.
The first order of business is to blow away all the dirt, then clean all the knobs, switches and the connections at the back with electronic contact cleaner.
Follow the service manual, I then replaced the transistors as follow.
- 2SA725s/2SA726s with KSA992
- 2SC1919s with KSC1845,
- 2SC1438 with KSC1845,
- 2SC1384 with KSC2690
- 2SD712 with KSC2073.
Next I replaced all electrolytic caps except the 2 big 8000uF/42V ( I don't have any handy).
One thing I learn during this exercise that replace the 220uF/63v with 390uF/63v (also don't have any 220uF/63v handy) will cause loud hums, so I put back the original 200uF/63V.
Searching for issues with SX-680 from this site, I replaced resistors R401 (33ohm) and R410 (100ohm) and replacing the Diodes D401/D402 10E2 with 1N4004 for good measure.
Once all of this is done. I start it up everything came up (except few light bulbs). Test few AM/FM channels all goods. Test Aux also good. All goods except 2 issues: 1) Only Left channels is working and 2) minor hums (audible when not play anything)
So I would think the right power pack STK-0039 would be dead. To test this, I swapped around the STK-0039.
Nothing changed, still minor hums, left channels still worked and no right channels. What!?!?
Measuring the voltage of the 2 STK-0039 , and they all seem within expected specs.
I also did try to replace the pair of 2SA798 with DIY combining 2 KSA992s and replacing the 2SK117 with 2SK30A nothing changed still so I ended up put them back.
At least, I and half way there (1channel to fix). I am running out of ideas, what to check and replace next and looking for help from collected wisdom/experiences here.