Sansui AU-555A Dead right channel

harobike

Member
2019-11-18 9:05 am
Hello,
I have my old sansui 555a, in which some time ago I replaced all electrolytic capacitors and most transistors. Everything was great, but sometimes the right channel stopped working. I noticed that the problem may be in the switches, so I bought Deoxit D100 and Fadergrease and cleaned all switches and potentiometers. I turned on the amplifier and heard a noise. I got nervous and decided to improve the soldering of two cables at the low filter switch, which I broke when cleaning. Unfortunately, after soldering, wanting to quickly check if it works, I did not connect the F-1272 board. As it turned out later, I didn't put on a metal cover on top. When I put it on, the noise was gone. But after soldering, there was no right channel either. Could I burn something without connecting the F-1272? I checked the voltages on the power transistors, on C819 and C820, I checked the fuses and everything is ok. The switch I soldered was checked many times and it seems to be ok. What could happen? :( What could I check to find out where the reason is?
 

nuryev

Member
2007-08-11 10:02 am
Hello,
I have my old sansui 555a, in which some time ago I replaced all electrolytic capacitors and most transistors. Everything was great, but sometimes the right channel stopped working. I noticed that the problem may be in the switches, so I bought Deoxit D100 and Fadergrease and cleaned all switches and potentiometers. I turned on the amplifier and heard a noise. I got nervous and decided to improve the soldering of two cables at the low filter switch, which I broke when cleaning. Unfortunately, after soldering, wanting to quickly check if it works, I did not connect the F-1272 board. As it turned out later, I didn't put on a metal cover on top. When I put it on, the noise was gone. But after soldering, there was no right channel either. Could I burn something without connecting the F-1272? I checked the voltages on the power transistors, on C819 and C820, I checked the fuses and everything is ok. The switch I soldered was checked many times and it seems to be ok. What could happen? :( What could I check to find out where the reason is?

Hi harobike,

:-( !! Not a good feeling! I've been there..

After cleaning inside my trusty old Marantz PM66 KI amplifier - I also heard a strange sound after powering on - followed by a peculiar smelling smoke!! Yes i had blown a channel. I am not as experienced or technically able to assist you with a channel rebuild.

But this is the interesting part - the very fact that I cannot assist you speaks volumes of my technical expertise or LACK thereof! Yet, I not only successfully rebuilt the blown channel, I also recapped the amplifier and it is still working well after handing it down to my son-in law!!! ;-)

Anyway - I would suggest downloading the schematic for the your amp. and getting familiar with the different location of parts and the part numbers and location on the pcb. DO NOT OPEN your amp until you have some confidence that you are able to do so safely! Some of the large capacitors are able to hold charge for a long time after the power has been switched off and the amp unplugged!!!!

After accessing the service manual and schematic diagrams - search on diyaudio for others who have experienced similar problems and go from there.

The fault could be anything from a blown transistor to dry solder joint or bad connection. There are some very highly skilled individuals here who are abe to assist. Do a search for Moolie
 

harobike

Member
2019-11-18 9:05 am
Thank you everyone for the reaction. Unfortunately, I didn't have an RCA jumper, I used the original ones all the time, so I couldn't switch channels. But I could pull out the jumpers and see what was going on. And unfortunately very strange things were happening. I decided to look at the wires at the switches and solders again. I improved soldering and made sure everything was OK. I also made new jumpers on RCA cables. And it turned out that everything works! Both channels are now playing. I have only a small balance issue. Maybe not balance but more sound, I don't know. It seems to me that the left channel plays more clearly. The right one seems to give less space, less middle and high tones. Maybe it's just an impression. But can it be measured somehow?
 
Both channels are now playing. I have only a small balance issue. Maybe not balance but more sound, I don't know. It seems to me that the left channel plays more clearly. The right one seems to give less space, less middle and high tones. Maybe it's just an impression. But can it be measured somehow?
Say hi to you new friend, Rightmark Audio Analyzer.

Careful with the volume, the headphone output can put out enough level to fry onboard line-ins in particular.