My Sansui 400 just stopped working
- Thread starter matmat
- Start date
Ok, there you go.
In my latest post I said powering through DBT will mess up the readings, because the bulb in series will eat up some voltage.
Does the bulb light up bright when you listen to a source with distortion?
I would not try to plug to regular outlet / normally, if it does light up bright. It means there's a major problem.
In my latest post I said powering through DBT will mess up the readings, because the bulb in series will eat up some voltage.
Does the bulb light up bright when you listen to a source with distortion?
I would not try to plug to regular outlet / normally, if it does light up bright. It means there's a major problem.
Hipocrates
Super Member
usually does...
Main reservoir filter caps makes the bulb bright at power on for few seconds, then dims down. It's normal behaviour.
Browsing some of your posts in this topic, you have put the amp back in regular voltage feed after replacing the outputs.
So, if the bulb is about as bright as back then (you can see filament in bulb easily, while powered) I'd say you're good to go. My take.
Always when working on the amp, like replacing components or whatever, it's good practise to test the amp through DBT before regular feed.
It's a cheap warranty
Browsing some of your posts in this topic, you have put the amp back in regular voltage feed after replacing the outputs.
So, if the bulb is about as bright as back then (you can see filament in bulb easily, while powered) I'd say you're good to go. My take.
Always when working on the amp, like replacing components or whatever, it's good practise to test the amp through DBT before regular feed.
It's a cheap warranty
matmat
Member
Yes, it looks exactly the same as it did after I replaced the outputs. I had also tested with the DBT then before I plugged to regular outlet then.
Now I just replaced the blown fuse, and the distortion is all gone, on both channels! Everything sounds crystal-clear! It's a happy day.
Although for some reason, I am still getting the same exact bias readings without the DBT. Should I worry about it, if everything sounds good?
I am tempted to put the cover back on, plug my turntable and my speakers, and call it a day... But if it's important to get this bias adjustment straight, I can wait.
Thank you everyone for your precious help thus far!
Now I just replaced the blown fuse, and the distortion is all gone, on both channels! Everything sounds crystal-clear! It's a happy day.
Although for some reason, I am still getting the same exact bias readings without the DBT. Should I worry about it, if everything sounds good?
I am tempted to put the cover back on, plug my turntable and my speakers, and call it a day... But if it's important to get this bias adjustment straight, I can wait.
Thank you everyone for your precious help thus far!
Great! It's progress - no distortion.
If you still can't adjust the bias to factory settings a problem remains with the unit.
You would get full potential out of it with correct bias setting, now it probably runs little cool and sound is a bit off.
Are the capacitors (caps) in the unit originals? It's nearly 50 yrs old, so if you have original caps fitted, they may have drifted a lot.
I have a Sansui 5000 from the same era, where I had a problem with bias adjustment on a channel. I had the exactly same issue.
Bias didn't dial into factory setting with new caps and after some time I realized those carbon resistors were also drifted.
One of the carbon resistors I think it was supposed to be 3.3 ohms had drifted nearly to 60 ohms. Carbon resistors are prone to drift a lot over time.
After replacing bunch of resistors I was able to adjust the bias correctly.
So if you take a look at channel driver board (ones with trimpots) and they are fitted with carbon resistors (picture) one of them might be a culprit for the issue or the original caps.
If you still can't adjust the bias to factory settings a problem remains with the unit.
You would get full potential out of it with correct bias setting, now it probably runs little cool and sound is a bit off.
Are the capacitors (caps) in the unit originals? It's nearly 50 yrs old, so if you have original caps fitted, they may have drifted a lot.
I have a Sansui 5000 from the same era, where I had a problem with bias adjustment on a channel. I had the exactly same issue.
Bias didn't dial into factory setting with new caps and after some time I realized those carbon resistors were also drifted.
One of the carbon resistors I think it was supposed to be 3.3 ohms had drifted nearly to 60 ohms. Carbon resistors are prone to drift a lot over time.
After replacing bunch of resistors I was able to adjust the bias correctly.
So if you take a look at channel driver board (ones with trimpots) and they are fitted with carbon resistors (picture) one of them might be a culprit for the issue or the original caps.
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slimecity
Super Member
Inmy expereince with getting bias readings, it can be tricky getting these in mA, when the manuals require this.
With amps like the 555a and 999 I just gave up and took the readings in mV accross the emitter resistors for the outputs. Perhpas others could chime in and see if that approach is recommended in this case, to double-check your readings here.
It seems unusual otherwise that the bias would be "off" if both channels are working and sounding OK....
With amps like the 555a and 999 I just gave up and took the readings in mV accross the emitter resistors for the outputs. Perhpas others could chime in and see if that approach is recommended in this case, to double-check your readings here.
It seems unusual otherwise that the bias would be "off" if both channels are working and sounding OK....
matmat
Member
I haven't replaced any capacitors or resistors, but then again I'm not sure what the previous owner did before me.
One thing I have noticed, is that while the sound quality is just as good as I can remember, its also a lot quieter than what it used to be. I have to turn the dial almost twice as far to get the same volume I used to.
One thing I have noticed, is that while the sound quality is just as good as I can remember, its also a lot quieter than what it used to be. I have to turn the dial almost twice as far to get the same volume I used to.
On one of my amps, not sansui though, time before I knew anything about fixing amps I had an issue which forced me to use volume knob at 13 or 14 o'clock position to get to any reasonable volume level, depending on the song of course.
At the time I didn't care as long as the amp kept working, but one day it started with horrible crackling sound and sound level even lower in the background.
I realized this is the point when I need to fix or trash the amp.
I can't tell you how floored I was after having replaced the caps and turned the unit back on. I replaced all the caps.
I got full volume power back and now I must keep the volume knob at max 10 o'clock position. It's a small 15w amp I use with my computer for near field listening.
It's a sign that some of the caps on your Sansui 4000 are nearing the end of their life.
You should at least replace the big filter reservoir caps. I would also replace all the rest of the power supply caps and driver stage caps.
If you do it, you won't regret it.
At the time I didn't care as long as the amp kept working, but one day it started with horrible crackling sound and sound level even lower in the background.
I realized this is the point when I need to fix or trash the amp.
I can't tell you how floored I was after having replaced the caps and turned the unit back on. I replaced all the caps.
I got full volume power back and now I must keep the volume knob at max 10 o'clock position. It's a small 15w amp I use with my computer for near field listening.
It's a sign that some of the caps on your Sansui 4000 are nearing the end of their life.
You should at least replace the big filter reservoir caps. I would also replace all the rest of the power supply caps and driver stage caps.
If you do it, you won't regret it.
As it's clear the amp is nearly 50 years old, so if you have time to tinker and work with the amp I would change all caps on all boards, if possible.
But now having recapped 5000 (all of the originals were grey ELNA caps), the caps were at worst condition on the driver stages (on 4000 board(s) marked F-1150).
I must say service manuals for Sansui amps seem to come with many minor errors, so if you are on the job for the first time, be sure the polarity of the cap will always be fitted the same way as the one you removed from the board. I think it'll be sloppy work if you pull them all out at once and then check from the schematic, since there might be errors. So take photos of the original caps fitted on board, so you have reference to check from. On 5000 there are two separate boards for each channel which were identical, so it was easy to remove all from the one board, then check everything from the other driver board. Maybe this is the case also on 4000.
The drifted (carbon) resistors are likely to be found from the driver stages, because higher voltage applied there. When you remove caps you also have more room to check the resistors. Pull one leg of the resistor out, if you don't see the values you should see, but some of them can be checked fitted in board.
These are probably most in need of new fresh caps:
F-1150 driver stage
F-1187 ripple filter stage (power supply)
F-1176 protector stage
Plus the large filters (4x 2200uF)
Target all of the "electrolytic capacitor" marked on the service manual.
Other types are not so important in terms of technical condition of the amp.
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matmat
Member
Hi all,
It's been a few months... I was traveling and couldn't deal with the receiver, but here's an update:
Shortly after my last post, the distortion came back on the left channel. I ran out of time and patience, and ended up bringing the receiver to a reputable repair guy in my area. I'm not sure what he did exactly, but he apparently fixed it: both channels were sounding fine when he returned the receiver.
Then, after a few minutes of playing, the same issue came back: distortion on left channel, and left fuse blown. I brought it back to him, he fixed it again, played it for hours at his place, everything ok. Then brought it back to my place, and again: distortion appears after a few minutes and fuse blows. He came to inspect my installation, checked the speakers and wires, but didn't find anything wrong.
Now I'm supposed to bring it back to him again, but I wonder, what could be causing the receiver to systematically blow a channel at my place, but not somewhere else? Is there something I should check or change?
Any help is appreciated!
It's been a few months... I was traveling and couldn't deal with the receiver, but here's an update:
Shortly after my last post, the distortion came back on the left channel. I ran out of time and patience, and ended up bringing the receiver to a reputable repair guy in my area. I'm not sure what he did exactly, but he apparently fixed it: both channels were sounding fine when he returned the receiver.
Then, after a few minutes of playing, the same issue came back: distortion on left channel, and left fuse blown. I brought it back to him, he fixed it again, played it for hours at his place, everything ok. Then brought it back to my place, and again: distortion appears after a few minutes and fuse blows. He came to inspect my installation, checked the speakers and wires, but didn't find anything wrong.
Now I'm supposed to bring it back to him again, but I wonder, what could be causing the receiver to systematically blow a channel at my place, but not somewhere else? Is there something I should check or change?
Any help is appreciated!
matmat
Member
Another update:
The issue keeps happening, and not just at my place like we first suspected, but in his shop the same way. He's replaced the heat sink transistors again, and surprisingly, the channel that kept blowing is now stable, but the problem somehow transferred to the other channel, that keeps blowing the fuse and getting distorsion after a few minutes or a couple hours of play.
The repair guy has no idea what is happening at this point, he's given up and is giving me back the receiver.
So back to square one. What should I do? Does this sound like a problem with capacitors like Nick was suggesting? Is it worth trying to replace all the "electrolytic capacitors"?
Again, any help much appreciated. I don't want to give up on this receiver!
The issue keeps happening, and not just at my place like we first suspected, but in his shop the same way. He's replaced the heat sink transistors again, and surprisingly, the channel that kept blowing is now stable, but the problem somehow transferred to the other channel, that keeps blowing the fuse and getting distorsion after a few minutes or a couple hours of play.
The repair guy has no idea what is happening at this point, he's given up and is giving me back the receiver.
So back to square one. What should I do? Does this sound like a problem with capacitors like Nick was suggesting? Is it worth trying to replace all the "electrolytic capacitors"?
Again, any help much appreciated. I don't want to give up on this receiver!
