give sansui A-80 a new life

hi ,just like to share some experience of restore sansui A-80,the set have on power but only got
 booming noise out from speaker.
before picture


all the part has been change as below picture


all part must measure by multimeter before instal,
i make a mistake forgot to check power cap 6800uf,it burn fuse in first time than find out one
of the new power cap short .
some transistor also discontinue ,have to find
replacement .
below is some picture after restore .


now a-80 is back in service

  thanks for viewing

chrischin wrote:hi ,just like to share some experience of restore sansui A-80,the set have on power but only got
 booming noise out from speaker.
before picture


all the part has been change as below picture


all part must measure by multimeter before instal,
i make a mistake forgot to check power cap 6800uf,it burn fuse in first time than find out one
of the new power cap short .
some transistor also discontinue ,have to find
replacement .
below is some picture after restore .


now a-80 is back in service  

  thanks for viewing

 Look like a table of medicines, nice job.

Hi Chris, great. How does it sound?

Hello Chris, I'm Federico from Argentina. I've recentrly bought one A-80. It works good, the sound is really beautiful in all the input sources but I havent't tested the phono input yet.

I opened the upper cover and I found some resistors are missed (perhaps burnt away).

I downloaded the electronic diagram and found those resistors are R62, R56 and R78. What do those pieces do? What part of the equipment do they control? I attached some photos.

What could have caused the problem there???

I'd appreciate if you could tell me the Ohms values because they disappeared.

Thank you very much and I hope you are OK.

Best wishes.

Hi Federico,

Resistors R56, R62 and R78 are from your right channel power amp circuit. If these resistors are missing you should not get any sound from your right channel speaker.

If you check back your schematic diagram the resistors value actually can be found on the left channel amp, R55, R61 and R77.
-> R56 and R62 are 82 ohms, R78 is 220 ohms.
To double confirm, you can check the resistors on your left channel amp to confirm the values are 82 and 220 ohms.

If these resistors were burnt, there are high possibility that transistors around your right channel amp already damaged (short circuit). Please check and replaced those damaged parts too.

R56 and R62 are from the differential input section, while R78 is common emitter voltage gain stage of your right channel power amp.

Hi Chris, thank you very much for you answer!
It's weird because both channels sound good even when I select Tuner, Tape 1 or 2, Aux.
If you ballance 100% right or 100% left, every speaker emit sound properly.
I'm thinking about replacing the resistors but i'm afraid to damage another section or component when I power it on again.
I'll look it over deeply to see if it was touched o modified with intentions...

Hi Federico,

Your right channel amp will not be able to function if these resistors are missing.
Maybe they were soldered on the bottom side of your PCB... 

Regards,
cslim

hahahaha yeah, you were right Cslim!! Thank you, they were soldered on the bottom, perhaps it was the easiest way.
I'm embarrassed not to have it opened before, but now it is a learning to me!
It goes the photo:

Best regards and till next topic! Thanks!

The color code of these resistors show 82 ohms and 220 ohms, match the value of schematic diagram.
These resistors are 1/6W type, although some manufacturer claim that they can withstand until 1/4W power rating. The original resistors at these locations are 1/4W type.

I guess the reason these resistors not solder on top side of PCB are due to their size and shape are different from surrounding parts, so will give impression that these area been repaired before. If you check back the transistors around these area, you can noticed re-soldering mark, indicate that they might been replaced before.

By the way, since your amp is working normally, not to worry too much, just sit back and enjoy!

Regards,
cslim

special thanks to this nice person CSLim,
bazofie great to hear from you have sansui A80 amplifier

Hi I lso have a black Snsui A80. one channel Plays fine. the other channel has low volume and distorted sound. please help

And also what to do about the 8v 0.3 amp bulbs behind the vu meters

Hi Ricky, it is hard to predict what actually happened to the distorted channel without actual checking it.
From the age of the amp, it can be as simple as in/out terminal solder crack, dry out electrolytic capacitors or power amplifier circuit malfunction.
Noticed your location from India, guess you might need to find someone to help you locally. Good luck!
p/s: sorry ChrisChin, hijack your post again...