Leave the ground pin floating if you put in an IEC power socket.
The best improvement you can make on these old Sansui amps is replace all small signal transistors. They add a substantial amount of background hiss.
The best improvement you can make on these old Sansui amps is replace all small signal transistors. They add a substantial amount of background hiss.
I will replace the caps, i ordered them a couple of days ago.. So you're saying no ground connection of power ground and amp ground?
Actually, unfortunately, i got another problem, i don't know if it's a new one or something already there (i didn't used it for years), but only one channel is playing. I am quite sure it's a new issue, 'cause even when i started repair it, months ago, i plugged a cheap speaker on the output to check, and i can't remember a dead out.
The left one is the good one, right is dead.
Out from the right one i got a really low signal, pretty distorted also. I don't know if that is crosstalk, it could be. Any hints-ideas from where to start?
I will check the 733's i soldered in the right channel meanwhile..
Edit
Almost forgot... The same with headphones..
Actually, unfortunately, i got another problem, i don't know if it's a new one or something already there (i didn't used it for years), but only one channel is playing. I am quite sure it's a new issue, 'cause even when i started repair it, months ago, i plugged a cheap speaker on the output to check, and i can't remember a dead out.
The left one is the good one, right is dead.
Out from the right one i got a really low signal, pretty distorted also. I don't know if that is crosstalk, it could be. Any hints-ideas from where to start?
I will check the 733's i soldered in the right channel meanwhile..
Edit
Almost forgot... The same with headphones..
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Super easy to localize with a scope. Don't have one? Separate the pre and power amps (right at the input of the 2SA798 transistor should be good) and tap the pre signal and see if it plays on another amp. Also inject a signal directly into your power amp to see if it can pass it. Beware - volume will be maxed out.
I scoped the pre, the outs are fine. It has to be the power amp.
Also, i got 170 mV offset in that channel against 30 mV on the good one. I think after recapping and adjustin with the trimmer it will be fine, but still no out on right channel.
I check the transistors now..
Also, i got 170 mV offset in that channel against 30 mV on the good one. I think after recapping and adjustin with the trimmer it will be fine, but still no out on right channel.
I check the transistors now..
Follow the signal with your scope. See on the schematic where it goes. Do you get signal after your 2SA733 transistors?
i don't know how to do that.. can i actually put the black lead of the scope on ground and the red wherever i want without damaging anything?
Yes.
I like to clip the ground part of the channel B probe to the chassis of the amplifier, and then remove the ground clip from the channel A probe. That way, you aren't tied down so much, and it's easier to reach things with the channel A probe.
Because ground is connected together on channel A and channel B on your scope.
I like to clip the ground part of the channel B probe to the chassis of the amplifier, and then remove the ground clip from the channel A probe. That way, you aren't tied down so much, and it's easier to reach things with the channel A probe.
Because ground is connected together on channel A and channel B on your scope.
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i see.. unfortunately i just got one probe, got the scope from a friend who didn't use it anymore, the lcd is actually freaky as well (the trace doesn't go straight, so it's impossible to evaluate anything but presence of signal..).
yeah, i know i'm quite a rookie.. 😀
yeah, i know i'm quite a rookie.. 😀
Yeah, well.. I actually fear to damage the Sansui, i don't know what kind of load the scope is.. Really no idea, so i prefer to be conservative..
I found a bad transistor, it's Tr08, a SD438. It has an open lead between base and collector.. Don't know if my method is right, probably it is not. I just check resistance and voltage drop with the transistor on the board, and if i see some strange result like open lead, or very low resistance, i desolder it and check it out the board..
Even if it is not the right procedure, or the most professional one, it's the only i know!
I found a bad transistor, it's Tr08, a SD438. It has an open lead between base and collector.. Don't know if my method is right, probably it is not. I just check resistance and voltage drop with the transistor on the board, and if i see some strange result like open lead, or very low resistance, i desolder it and check it out the board..
Even if it is not the right procedure, or the most professional one, it's the only i know!
Sounds probable. Replace with KSC1845. While you're at it, replace all small NPNs with this part. 😉
KSC2316 is supposedly more suitable to replace THIS particular transistor, but I'm sure the 1845 will cut it just fine.
KSC2316 is supposedly more suitable to replace THIS particular transistor, but I'm sure the 1845 will cut it just fine.
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Thanks, Welcome.
I got some 1845 in the lab, i can try replacing it and look if it works.. I can always order 2316 next time i have to order something..
I got some 1845 in the lab, i can try replacing it and look if it works.. I can always order 2316 next time i have to order something..
I changed it with a 1845, now there is actual audio output, quite distorted though...
It's a huge improvement, but i continue to search for bad transistors.
Or can it be that the 1845 is not appropriate?
Edit
Tr10, the PNP in the same stage of the bad sd438 has the same problem, no drop between B-C. It's a 2sb560. As pnp i got just some 2n5401 and i do not believe i could use it. But what would be more suited in your opinion?
Thanks to all of you..
It's a huge improvement, but i continue to search for bad transistors.
Or can it be that the 1845 is not appropriate?
Edit
Tr10, the PNP in the same stage of the bad sd438 has the same problem, no drop between B-C. It's a 2sb560. As pnp i got just some 2n5401 and i do not believe i could use it. But what would be more suited in your opinion?
Thanks to all of you..
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Crap, I failed to notice the big difference in max collector current. It's 0.7A on the 2SD438 and 0.05A on the KSC1845. Well, since it works, you might as well replace its companion (2SB560) with KSA992, if you have one.
But beware - I'm not sure how reliable these will be here, until someone more knowledgeable chimes in.
Anyway, the proper replacement should be the KSC2316 I mentioned earlier, as well as its companion KSA916 for your 2SB560. But again, you may well be fine with what you've got right now. All the other specs match. I'm not sure how important max collector current is in this particular application...
But beware - I'm not sure how reliable these will be here, until someone more knowledgeable chimes in.
Anyway, the proper replacement should be the KSC2316 I mentioned earlier, as well as its companion KSA916 for your 2SB560. But again, you may well be fine with what you've got right now. All the other specs match. I'm not sure how important max collector current is in this particular application...
in my country i find easily the duo 2sd667-2sb647 or 2sa965-2sc2235 to replace the 2sd438-2sb560 i need to substitute..
i think i order both, nice to have some spare parts anyway..
i think i order both, nice to have some spare parts anyway..
Hey guys,
I replaced the 438 and the 560, the first with a 2sd667 and the latter with the same model.
Now the amp works!
Still waiting for the caps, though.
Got a last question: the amp becomes hot aft just some minutes.. Quote hot i would say.
I haven't tried yet to run it more than 20 minutes or so. Is it normal? I dunno how it was before, it's the first time i hear it. I hope it's not beacuse of some replacement i used... Really dunno.
I replaced the 438 and the 560, the first with a 2sd667 and the latter with the same model.
Now the amp works!
Still waiting for the caps, though.
Got a last question: the amp becomes hot aft just some minutes.. Quote hot i would say.
I haven't tried yet to run it more than 20 minutes or so. Is it normal? I dunno how it was before, it's the first time i hear it. I hope it's not beacuse of some replacement i used... Really dunno.