I have a sansui 8080 that I know sounds great. But at lower volumes the sound is rather distorted. I looked up why this might be and found that the bias may be off.

So I went and checked it out. I got 3 ma and 4 ma and could only adjust till about 6 ma....This is wayy off from the 30 it's supposed to be. Does any one know why this might be and what the fix is?

Any help is greatley appreciated,
Rudy

Also: I tried turninng up the bias to 6ma wild playing music. The sound definatley improved which IMO is a good sign.

If you were using a auto ranging DMM ..Manually put it DC amps..And recheck your bias.

I was using an auto range one but I can't manually set it to anything other than ac or dc amps.

So I made sure it was set to dc and also recalibrated teh zero point on the meter. The new reading gives me around 17 ma peak. And I can hear the difference very clearly when I set it to low ma and then crank it back up to 17.

Now just to get it from 17 to 30 :yes:

Are the output transistors getting very warm?

No they are keeping rather COOL actually. I have been letting it play music(at a moderate level) for about 10 minutes and they havn't even warmed up.

I was reading somewhere else and some one mentioned a diode that would be near the bias and DC offset controls but it was a very jumbled forum so I couldn't get any real solid facts out from it. Sound familiar...maybe?

Rudy

With the fuses 7 & 8 installed what DC voltage do you measure at the same fuses? Whats the DC offset(balance)..Look like ?

53.4 vdc from chassis to the fuse

That sounds about right...:scratch2: Have you got the same voltage on F09 and F10 except opposite polarity?

Yep exactly the same but opposite.

THe switches are rather dirty sounding too I'm gonna try giving them a spray. See what that does for Sound Quality.

Excuse my ignorance and possibly erroneous conclusion, but are you not suppose to be checking for DC millivolts for bias and having the meter set for millivolts not amps? Every bias I have done have been a test for millivolts. Are 8080 tests different for some reason?

Yes you have to put your Ameter in place of the fuse that the output transistor draws its power through. Not sure why they chose to do it this way, but Thats the way it's done on this beast .


Cheers,
Rudy

Pull the driver board and check all the fuse resistors. These receivers have a habit of the 22 ohm, and the 390 ohm resistors going bad. There are also a couple of 10 ohms resistors as well as 4.7 Ohm, all the fuse resistors are blue and will be raised off the board.

Excuse my ignorance and possibly erroneous conclusion, but are you not suppose to be checking for DC millivolts for bias and having the meter set for millivolts not amps? Every bias I have done have been a test for millivolts. Are 8080 tests different for some reason?Sansui does it a little differently.. You measure the milliamps at F07 and 08.I asked him to measure the supply voltage with the fuses installed suppose to be about +53 vdc.And -53 at F09 and F10. When you adjust bias,you are adjusting quiesent current.Most bias adjustment procedures have you adjust the voltage ie millivolts across a know resistance . voltage / resistance = current..

And when you find those out of range resistors and replace them, turn the bias pots back down before you power it up again, or you will cook some chit!

Haha thanks for that tip Paul,

And thanks to Avionic And CDfixer, your help is greatley appreciated.
I'll report back when I see whats happened to that driver board

Till then Cheers,
Rudy

Rudy

Haha I like how the baord just comes out like a Super nintendo game. Maybe I'll just pop Star Fox in instead of the driver board :P


Also just curious. When you guys are testing resistors do you pull them from the board first?? Or do you test it some other way. I've never been to sure what the best way to do it is. (I know leaving them in gives you the wrong readings)

Should not make a difference on the ones were talking about. If you get other than what they are supposed to be, they are trash! But yes, sometimes it's hard to get the propper reading in circuit.

Okay so the results are in:

390ohms now 408 and 402 ohms

22 ohms now 18.7 and 21 ohms

8.2k now 8.3.

10 ohms now show no reading. (blown)

and as for the 4.7 all mine come in very close to 4.7.

SO which do you think should be replaced?? Obviously the 10 ohm, 22 , and maybe the 390? If they're cheap enough at the store I'll do all of them, but if not, Only the crucial ones.

Tell me what you think

Cheers,
Rudy

They should be dirt cheap! Do yourself the favor and replace all of them. 1/4 watt flame-proof or even carbon film will do the trick.

Sounds good then. I'll hopefully post back later tonight with how things went.

Thanks again guys!

Rudy

Wiiiicked! I replaced the 22 ohm and 10 ohm resistors. They were the only ones the store had, luckily those two were probably most in need of a change anyways.

Now I can definatley get 30 ma of current, but it never seems to settle down and stay. It just keeps going up slowly but surely. Even after 6 minutes or so. So I set it down to 28 just to give it a bit more room to go up. Other than that sounds great! :D

I've had this amp around for 3-4 years and have tried troubleshooting and fixing it before and FINALLY! I have it sounding good, like an amp should. Now the only thing I need to figure out is why the front lights don't turn on :scratch2:

Thanks for the help! :thmbsp:
very much appreciated

Rudy

Allow at least 15 minutes prior to checking current, do you have voltage at the light bezel circuit board? {about 8v?}

hmmmm better go shut it off then and recheck that.

As for the lights at the front. I dono what the light bezel circuit is. But I know that there is one exact spot when you are turning the selector switch where the lights suddenly work.

The am, fm, dolby, aux lights allways light up as they should.

I'll look at the manual try to find that bezel board and see if it has 8 volts.

Cheers,
Rudy

The bezel referred to would be the plastic housing with the circuit board behind it as in this picture. But if you can get the lights to come on at a certain spot in the selector switch then that is obvious. Clean the snot out of that switch with De-oxit and rotate the switch until your hand is numb.

This is an old picture from an 8080DB showing the input lamps, the dial lamps are under the plastic housing. It would not be a bad idea to resolder the connections on that circuit board as they are known to crack over the long haul.

I am not very knowlegable about electronics but the one thing I can always fix on thes Sui's is front lamp lights. Almost always - reflowing solder fixes them :yes:

Ummm, that one spot the lamps works is when the selector is on the radio function?
That is normal operation, Sansui didn't light the dial face when the selector is on aux or tape.
Casey

I am not very knowlegable about electronics but the one thing I can always fix on thes Sui's is front lamp lights. Almost always - reflowing solder fixes them :yes:

Quite right Shacky...always seems like the left side {nearest the tuning meters} fixes them in my experience.

Well I tried cleaning it....that was No help. Helped the sound quality slightly though :P


The spot where it lights up is in between aux and tape I think. It's NOT next to the FM or AM. This makes me think the switch may be broken or jammed. Not too sure.


I'll try getting those front lights checked out and soldered up soon. The left power meter, closest to the tuning dials has been out for a while. Maybe that's why :D

I'll report back soon
Cheers,
Rudy

So I still have this giant sansui beast sitting in my living room. I have connected a couple different speakers to it and it and always find myself really messing with the treble and midrange controls and it still sounds "noisy".

So I was wondering if the 8080 should sound better than a AU-101. I picked up an au-101 for 5$ and I think the sound quality blows away the 8080. Do you think that seems right? Or does the 8080 definatley need some more troubleshooting/service??

Hopefully some one who has heard both can chime in.
Cheers,
Rudy

The red dot diodes are known for failing and causing bias control problems. They can be replaced by a pair of 1N4148 diodes in series. Also, TR07 and TR08 are mounted on the heatsink for one of the drivers on each side and compensate for temperature. If bad, these can cause bias to drift. These 2SC984s are hard to find, but there are substitutes. I used PN2222As and they work, but were a pain to install with good contact to the heatsink.

The tone controls are a little bit of a pain to get into, but can be done. Clean that sucker again. No way should the 101 sound better.

Ohhhhhh noooooo........

The bias on one channel was 21ma at power up. And steadily began increasing. By the time it made it to 33ma I decided it wasn't going to stop(about 10 minutes)

The bias on the other channel was 210ma!!!!!!!! :saywhat: This was with the bias pot turned all the way down. Turning it up made little to no difference.

It seems like my previous repair opened a whole new can of worms. Thankfully the amp still works. Most people wouldn't think twice about this amp, but I know it should sound better.

I will pull the driver board. Check all the repairs I did before, and then check the parts that Trwham mentioned.(would those parts affect sound, or just stabilize bias?)

Cheers,
Rudy


So I checked some stuff and didn't wanna post again. The red diodes seemed to be working. Checking them with my voltmeter showed they dropped .7 volts one way and did nothing the other way. So those seem OK. As for tro7 and tro8 I have almost no idea as to how to test those or if I even can with just a voltmeter.

Everything else seems OK. Checked all the electrolytic s with an esr meter and the only oddity was that the higher voltage 100uf capacitors had a lower esr than the lower voltage 100uf caps. Ideas???

Silly me. The biasing instructions were opposite. And the adjustments I made were affecting the other fuses ma.

So everything can be set to 30 ma. But it does drift upwards slowly but surely.

I also checked tr07 and tr08. From b-c and b-e it tests as diode. But it also tests as a diode from e-b which seems wrong to me.....Toast??


And does any one elses 8080 warm up. Seems like a funny thing to ask I know, but my 8080 does not let off any heat at all. Even after a few hours of running its still cold. I'm not exactly pushing it hard(maybe 10 watts on the meter) but I would expect it to be warm. Any thoughts on that? Not that a cool running amp is bad. Just seems odd.

You checkin that transistor out of circuit? If not, do that. If you are indeed checking it out of circuit, it is trash. As far as the bias creeping up, it will till it warms up and then it should settle back down. I adjust units about every 15 minutes till It stays. Could take an hour or better.

Have any of the vintage electrolytic caps been replaced? They may be getting toward the end of their lives. I think the driver board has a few. I have not worked on any of my Sansui receivers for a few years. As I read the first few threads, the first thing that came to mind was that if the amp was distorted at low volume, most always bias. But you have to find out why...

HMMM, I am finding this thread very interesting my 9090 sounds a bit harsh. The highs are actually quite irritating I have been describing it as too bright. I too am constantly fiddling with controls........
Picked up a Pioneer sx 3800 flouroscan at GW and just finished with a clean up and adjustments to Dc offset and bias. No doubt about it the Pioneer sounds way better and it probably shouldn't. I think I am going to really let the Sansui warm up and recheck the bias again. Not sure where to go from there though.:scratch2:

you describe what I am hearing almost exactly. It's strangly harsh. And I need to turn the mids waaaay down. And it's OK. And sometimes the treble has to be turned down to. What gives right?

And if you have set the bias once. You have probably heard all the benefits of it already. This amp sounded much worse before. Completely unbearable at low volumes. Setting bias properly was a 10x improvement in sound quality. But after a while I realized it's still not 100%.

I even just spent the past 3 hours figuring out how to get to the volume, treb, bass, ect... controls. Sprayed them for a whole movie and worked them all. My efforts helped slightly. All the controls work brilliantly now but sound hasn't really improved.:thumbsdn:

So must be some dried up capacitors(none replaced, by me at least). On the driver board there are 6 electrolytic capacitors. 100uf 80v 100uf 6.3v and .47 50v for each half. The 80v is a filter capacitor. No sound going through that one. The other two seem like they are in the chain of audio. So those are the ones I'm focusing on. I should also have those 2 on hand so I will be reporting with some interesting results sooner than later.

Also my bias does stabilize after about an hour, like Paul said.. So don't have to worry about that anymore thankfully. Just the lights left to figure out :scratch2:

Rudy

These are some threads I have on AK chasing this problem. I really haven't had time yet to try the Pioneer with Cds I am using as a reference in seeing if I have made improvements but hands down the sound was overall better.

Speakers:
http://www.audiokarma.org/forums/showthread.php?t=272443

9090 adjustments:
http://www.audiokarma.org/forums/showthread.php?t=273059

The source CDs and players:
http://www.audiokarma.org/forums/showthread.php?t=274083

I am curious to know if we have the same issue!

Regardless the Pioneer sounds better than the Sansui and that is disappointing at this point.........

Ok so I read your posts and it seems people were concentrating more on your Speakers and Source than suggesting an issue with the amp. And I suspect the amp. I have tried a few speakers with this amp and get the same results on all of them.

So I went ahead and tried changing the .47uf capacitor on the driver board. Results were not day and night. And switching back and forth between speakers did show a "slight" improvement. I also used a metal polyester instead of electrolytic. So it could just be the higher quality capacitor....

One thing "you" can try though is cleaning the pre out/in jumpers/inputs with deoxit. When I originally acquired this amp I thought they were welded in. And when I pulled them out just today they were pretty stuck. Cleaning made them go in and out smoother. A good sign that some corrosion has been eliminated. Sound seemed improved. But this could be a placebo effect. So I want you to try it out(if you havn't already) but only do 1 jumper, don't even pull the other one out. That way you can actually compare.

And for the more experienced recappers. Do you think this kind of noise/harshness could be caused by a bad power supply capacitors. I've heard of upgrading power supplies to get superior sound quality, but can you really hear a dramatic difference?

I'll be doing some more schematic reading to find some more audio chain capacitors. I'm pretty determined to fix this. I've put it off for long enough.

Hope that helps!
Rudy


Edit: Switching back and forth between speakers showed that replacing the .47 uf did actually help. It's a little louder from that channel and a bit more defined sounding. I will try with other speakers to verify this.

Edit: Different speakers do verify this. It is actually loud enough that my girlfriend notices the difference. Replacing the other .47 will further verify this.
Unfortunately that probably means that my amp needs recapping. And if yours is very similar. And nothing else seems to help. It probably needs new capacitors also.

Re-cap the entire unit is my rec.

Yea that seems like the right thing to do.

This thread will pop back up eventually, and hopefully with good news and results.

+ Working lights!

Rudy

Yes, well um placebo effects and paradigms all human conditions. I myself am listening to the same CDs that sound bright and they are still bright with this receiver. I am going to try and get these symptoms down correct before I try much else. I know for me it seems I am back where I started but I have been listening to this Pioneer for several hours and am not sure if it sounds as good now as it did when I first turned it on. Is this me or is this receiver sounding different warmed up maybe it is my speakers when they are warmed up? I can say the sharp bright highs are still there for sure. Maybe my ears are even getting fatiged...:scratch2:

Just a note on my 2 pennies. Don't re-cap a receiver until you have it working properly. Recapping a receiver that has problems is fraught with things that can go wrong. You will not be able to tell if the problems you have are from the recapping or not. Fix the bias problem before trying to recap.

Bias issue was totally made up in my head :screwy:

After an hour it did settle down and stay still. I set the bias some time ago and when I checked it again just yesterday. One side was reading 210 ma!
That combined with me forgetting that the bias instructions I had were written wrong, lead me to believe that my previous repairs had created a whole new list of problems.

Thankfully not though :banana:


And Bigkahuna. I like you feel back where I started. When I set bias originally I thought WOW what a nice sounding amp. Then after some time I convinced myself it should be better. And after switching that .47 capacitor I've once again convinced myself that it does sound good/better.

It's funny how the mind works. But I'm sure that in enough time I will think it sounds poor/broke again. And recap the entire thing in the quest for the ultimate sound.

Alot of people say if it's not broke don't fix it. So I'll wait till it's "broke" again :thmbsp:

Cheers

I can tell you first hand how subjective humans can be when trying too diognose something. I used to work in the automotive field doing fairly complex work. In my earlier days it was automatic transmission repair and overhaul and then drivability fuel injection and emission controls. A missed diognosis is the start of an expensive and bad customer experience. Human subjectivness caused an awful lot poor diognosis in that feild. If a technician drives the car and has some idea of what might be the cause he will try to prove hopefully through testing that what he thinks is the cause actually is. This is where skill and expereriance comes in. A good technician will have the skills to prove with little doubt that the XXX is actually the cause. The poor technician basically not knowing how things work doesn't then know how to actually test something. These were the guys that would bring the car in that needed a spark plug wire and blame the problem on the computer. Being the most complex device the rationality here is that this is the best guess. In other words the best odds fo being where the problem is. But, whether we are talking about a good technician or a bad technician either one COULD set themselves up for a misdiognosis.

As humans we tend to think something and then that colors our percetion of reality. The auto technician can think something with the XXX is wrong and then try to prove it by what ever means he can. Could be a tab that mounts it is broken could be that there is green junk all over it could be that the voltage that it should be off is just a smidge. All of these things could be the problem and all of them might not. As humans we are going down that track and aren't going to look other areas because we have percieved we are in the right area. Our perception colors our reality.

BTW I myself feel like I am the parts replacer. These electronic devices are fairly complex and I myself am beyond my comfort zone. But I find it all interesting so that is where I want to be. Wow that all turned into a little thesis!!!

I would just like to say that my Sansui 8080 sounds freaking great.

I didn't do anything else to it. I've just come to love it. And I use it in place of my Fisher 400 95% of the time. It was most likely just cr*p speakers hooked up. That at the time I thought were OK. Or maybe some other voodoo magic occurred :scratch2:



Go Sansui :banana:

Cheers,
Rudy