Hi,
I've just bought a 7070 off craigslist... without... testing... it... as seller says it's working fine, and met me at a gas station. The cosmetic of the 7070 is pretty good, so I did not suspect anything too off with it...
My mistake. Went back home and plugged it in. First thing I noticed was non of the lights came on. Then I found the power output(from the meter) on left channel is higher than that of the right one without any input connected to the 7070. I followed the service manual and found the DC voltage of the left channel was way off. Adjusted it back to ~0mV according to SM then moved on to bias current, but I could not get a reading with my craftsman 82141 multimeter. The meter kept reading 0.
After 30 minutes trial of no success, I decided to try connecting the 7070 with my test speaker. As I plugged in my test speaker to the 7070, I can hear a hum from the speaker as soon as I switch the speaker selection on. The hum goes louder when I crank the volume on. I tried unplugging the plug and plug it in after switching polarity, and the hum gets quieter, but still there, still varies with volume. I was able to get sound from AM and it did not sound distorted (well, not sure how accurate I'm hearing, since I'm using a spare speaker which cost nothing, But at this point, I wouldn't connect anything better to the 7070)
Questions,
1. With all the lights off, does it means it should be more of the problem with the board? I found a previous thread about re soldering the board and cleaning some fuse holder. I did clean all the fuse and holders on F-2625, as I didn't know which one is was, but that didn't help.
2. Will I be able to get sound from the receiver if there is no bias current at all? Or I should probably borrow another multimeter?
3. From what I've read, if the hum varies with volume, it should be from the preamp section, correct? I've also read some posts about grounding issue, and changing polarity of the power plug did helped a little with the hum, so I'm confused. (of course, I am hoping it was just a grounding issue as that may be easier to fix)
Well, I do hope these are going to be fixable by myself (not experienced with electronic works though). I certainly did pay way more than a parts unit, and I hope I won't have to spend a whole lot getting it to work properly.
This is my first Sansui receiver. I've been a fan with vintage, and I have used, and am still using vintage setup in my system. I do hope I can at least get to know the sound characteristic of Sansui!
I've just bought a 7070 off craigslist... without... testing... it... as seller says it's working fine, and met me at a gas station. The cosmetic of the 7070 is pretty good, so I did not suspect anything too off with it...
My mistake. Went back home and plugged it in. First thing I noticed was non of the lights came on. Then I found the power output(from the meter) on left channel is higher than that of the right one without any input connected to the 7070. I followed the service manual and found the DC voltage of the left channel was way off. Adjusted it back to ~0mV according to SM then moved on to bias current, but I could not get a reading with my craftsman 82141 multimeter. The meter kept reading 0.
After 30 minutes trial of no success, I decided to try connecting the 7070 with my test speaker. As I plugged in my test speaker to the 7070, I can hear a hum from the speaker as soon as I switch the speaker selection on. The hum goes louder when I crank the volume on. I tried unplugging the plug and plug it in after switching polarity, and the hum gets quieter, but still there, still varies with volume. I was able to get sound from AM and it did not sound distorted (well, not sure how accurate I'm hearing, since I'm using a spare speaker which cost nothing, But at this point, I wouldn't connect anything better to the 7070)
Questions,
1. With all the lights off, does it means it should be more of the problem with the board? I found a previous thread about re soldering the board and cleaning some fuse holder. I did clean all the fuse and holders on F-2625, as I didn't know which one is was, but that didn't help.
2. Will I be able to get sound from the receiver if there is no bias current at all? Or I should probably borrow another multimeter?
3. From what I've read, if the hum varies with volume, it should be from the preamp section, correct? I've also read some posts about grounding issue, and changing polarity of the power plug did helped a little with the hum, so I'm confused. (of course, I am hoping it was just a grounding issue as that may be easier to fix)
Well, I do hope these are going to be fixable by myself (not experienced with electronic works though). I certainly did pay way more than a parts unit, and I hope I won't have to spend a whole lot getting it to work properly.
This is my first Sansui receiver. I've been a fan with vintage, and I have used, and am still using vintage setup in my system. I do hope I can at least get to know the sound characteristic of Sansui!