Sansui Receiver 881 Power Supply Board problem.

[QuiDaniel]

Hello from Peru. I own a Receiver 881, but it does not make a sound.
Few years ago the receiver start to put on security mode (the security relay in the F-2437 power supply circuit board click and the sound goes off) when this happened it was connected to my audio device (Focusrite Scarlett 2i4) in the aux jack and I was playing my guitar using the receiver as an amp and the speakers were the Sansui's SP 2500 X... I turn it off and on again and it sound for like 30 min then the sound goes off again and again and so... the time when the receiver sound was getting shorter as the days goes by... and no technician could find the problem, now it does not sound at all... I hired one last guy to take a look at it, make me buy a new security relay (that was an odyssey to buy) put it and then replace it again with the old one... OMG that one really piss me off, and some other stuff to but the problem persist... So now I'm starting to lose my mind trying to find the solution... any one here can help me?? please I need my receiver it means a lot to me... and here in Peru I couldn't find a specialist in Sansui, only a couple of guys that know electronics, but no vintage audio equipment particularly... So please! I really need help... I know one of you guys have the answer.

If you can help me, when you visit Peru, I will make you a ceviche that will blow your mind

Thank you for your time.

 

[slimecity]

Ola amigo. Whereabouts are you in Peru? I visited there a couple of years ago, the cerviche is great!

If the protect circuit is activating the LAST thing that I would look at is the relay.

The circuit is either activating most probably because (a) there is too much DC offset voltage going to the speakers, and the circuit is telling the relay to click off to protect the speakers, or (b) there is a fault with the protect circuit. The former is probably more likely.

So what you need to do for starters is: find and download a service manual for this model - here it is (you will need to create an account but the service is all free):

https://www.hifiengine.com/manual_library/sansui/881.shtml

Next step, follow the procedures in the manual for testing the DC offset. You will need to have/buy a small screwdriver and digital multimeter to do this.

If the relay has clicked "ON" then this should be easy - but based on what you are saying, the relay isnt clicking ON. So you need to get inside the unit, find the points where the amplifier outputs go to the relay and measure the DC offset there for each channel (this is hard to explain but if you post some pictures of the unit underneath the relay we can show you how to do this).

 

[QuiDaniel]

Hallo vriend! I live in Lima... I assume that your plane landed here and then you travel to Cusco or the north beaches, they are gorgeous... Anyway thankyou for your help, I really need it.
I downloaded the service manual and in the page 4 there is the 3-1 Driver Circuit Board Adjustment... Is that where I'm suppose to look for the DC offset?

Once again thankyou so much for your help.

 

[QuiDaniel]

Ola amigo. Whereabouts are you in Peru? I visited there a couple of years ago, the cerviche is great!

If the protect circuit is activating the LAST thing that I would look at is the relay.

The circuit is either activating most probably because (a) there is too much DC offset voltage going to the speakers, and the circuit is telling the relay to click off to protect the speakers, or (b) there is a fault with the protect circuit. The former is probably more likely.

So what you need to do for starters is: find and download a service manual for this model - here it is (you will need to create an account but the service is all free):

https://www.hifiengine.com/manual_library/sansui/881.shtml

Next step, follow the procedures in the manual for testing the DC offset. You will need to have/buy a small screwdriver and digital multimeter to do this.

If the relay has clicked "ON" then this should be easy - but based on what you are saying, the relay isnt clicking ON. So you need to get inside the unit, find the points where the amplifier outputs go to the relay and measure the DC offset there for each channel (this is hard to explain but if you post some pictures of the unit underneath the relay we can show you how to do this).

slimecity my friend, I follow the service manual procedure and nothing... put the multimeter everywhere the manual said and as you told, nothing... because the relay wasn't clicking ON... but I was checking everything, and by chance I took a fuse out and the Receiver turn on... it was the right channel fuse (board F-2437 fuse F10)... so I guess there is something wrong with that channel... I have no idea on what to do next... any tip? anyone?

Another thing, the Receiver has a lot of hum coming out from the left channel.

 

[ConradH]

The 881 was made about 1975, so it's 42 years old, give or take a year. The first thing I'd do is pull the power board and change the capacitors. Pull the power transistors off the heat sink, clean them, test them with a DVM on "diode check", and then reinstall them with new thermal grease and insulators. Normally I'd trouble shoot first, but it doesn't sound like you have anybody well equipped to do that, so at least get the power board in good shape. use a bit of Faderlube on the trimpots, then adjust bias (and offset if it has it). Check the power supply voltages. Make sure screws connecting boards to the chassis are snug- some are used for grounding. See what the status is then.

 

[slimecity]

What I would also do (after following ConradH's advice) is build a dim bulb tester and only power the unit up using that. There are instructions on this site for making one. Use a 60-100W incandescent lightbulb.

This will protect your output devices, especially when you set the bias as the trimpots could be bad, you will know once you get to this step.

 

[QuiDaniel]

The 881 was made about 1975, so it's 42 years old, give or take a year. The first thing I'd do is pull the power board and change the capacitors. Pull the power transistors off the heat sink, clean them, test them with a DVM on "diode check", and then reinstall them with new thermal grease and insulators. Normally I'd trouble shoot first, but it doesn't sound like you have anybody well equipped to do that, so at least get the power board in good shape. use a bit of Faderlube on the trimpots, then adjust bias (and offset if it has it). Check the power supply voltages. Make sure screws connecting boards to the chassis are snug- some are used for grounding. See what the status is then.

Thank you so much, you dudes in audiokarma are the sheeeeeeeeet!
I will have to undust my electronics books and start relearning everything... I'm very scare of this... overwhelm if you wish... I know a little of electronics (I am a industrial engineer) but this is by far the hardest thing I ever try on this field... not mention the fact that 2 very nice strangers are helping me in my 2nd language, one in another continent to do it... life is funny sometimes

ConradH I really appreciate your time, you're very kind. Do you recommend me to pull the power transistors off from both channels? What it is exactly trouble shoot and what would I need for this? I have some tools available and I have the balls to do this... I don't know how but I will overcome this

So... I'll go and learn something about capacitors & transistors and... I'll be back

 

[QuiDaniel]

Hi guys, I was reading about this recap and found a lot of info some pro , some against the recap... I know that I have my hands tied because my receiver is broken, but I want to be sure about everything before I start, so I have some questions that I need to ask, I'd appreciate some help:

1. Is the receiver going to be alright? quality lost? the working temperature is going to change? It will be good as new?
2. Do you recommend any brands or type of electronics?
3. Do I need to take some extra precautions that I'm not aware? I have done some soldering and resistor replacements before, but never in a 42 years old thing...
4. All the components are very clean, what's the first thing that I'm suppose to check, take off or just measure?

Thank you for your time once again, I attached some pics form the boards so you can see what I'm going through... the one with the fuses is the one that I mention before (board F-2437 fuse F10, first of the right), just FYI.

 

[ConradH]

The receiver can be alright, no quality lost, almost as good as new, but it will still be 42 years old. Whether that happens depends on what happens next. I suggested working on the power amp board because it's easy and might resolve some problems. Normally I'd say change nothing until you've troubleshot the problems- don't know if you have a scope or the knowledge to do this. There are all sorts of things you might not be aware of, but if you go slow and check back here. lots of people can give advice and help.

 

[QuiDaniel]

Thank you Conrad, you are the true server of evil... I read your web, that was exactly what I was needing... pretty cool explanation and by far the most sincere words I heard about the topic...

After reading your web I realize that I'll not do this... I don't see a scope since college and I don't have access to one at this time... I'll end up changing everything just by not knowing what is broken and what's not... oh well... at least I now know what's wrong with it... no one can fool me with the fixing of the problem, all thanks to you guys... If anyone from Peru who knows someone that can repair my receiver read this, please send me a PM.

I just have to wait until I find someone who can have the job done

Once again, thank you guys, you help me a lot... I'm not worthy it!!!

Regards,

Daniel