Syn_Error
New Member
This is my first post here on AK. However, I've been lurking and reading through many posts and messaged a couple other members and feel right at home with everyone. I'm planning on rebuilding an SX-737 I picked up a few months ago. I got the unit and used it with a turntable, a bluetooth receiver/transmitter, and FM radio. About a month ago, it started to act up such that after about thirty minutes or so, it would develop a crackle in both channels and then produce a loud pop and then silence. I would be able to turn it off for about five to ten minutes and turn it back on with no problems. But another fifteen or so minutes, it would crackle and then pop again.
I decided to go ahead and replace Q1-10 on the Power Amp Assembly (AWH-033) after reading 2SC1451 and 2SA726 are problematic. This has been done and everything checked out with the DBT. However, while looking at the diagram of this board, I noticed two resistors that are on the diagram but not in my board. Specifically R17 and R18. Both are marked as 15K on the diagram. There is an indication on the silk screen as to where they go. On the bottom/foil side, there is solder there, but no indication that these resistors were ever installed. AK member Motnick, theorized that as mine is a '75 model and his a '74, there may have been a revision and those were taken out of mine. I'm not sure if this is any way critical to this board. I asked Mark about it and he suggested I post this on the forum and ask everyone. It doesn't seem to be an issue, unless this is what the origin of my crackle/pop turns out to be.
After replacing the transistors mentioned above, I'm still getting out of spec voltage readings on this board. (AWH-033)
Pin 6: 32.7
Pin 10: -13
Pin 33: 26.3
Pin 28: -26.3
Pin 29: -26.3
Pin 25: -26.3
Pin 22: 26.3
I was able to get 3 and 17 to 0 and 1(2) and 18(19) to 20mV as per manual and corrected instructions from the forum.
I suspect my voltage issue will be originating from the Power Supply Circuit Assembly.
(AWR-057)
Pin 14: 32.6
Pin 15: 28.4
Pin 16: 28.4
Pin 17: 21.3
Pin 19: 13.6
Pin 20: 13.6
Pin 21: 13.6
Pin 12: -13
Pin 13: -13
Pin 7: -27.5
Pin 10: -26.3
Pin 9: 26.3
I'm thinking I'll have to recap AWR-057 and subsequently other boards. I've kept up with Motnick's rebuild and I'm taking that as some inspiration to get this thing working better than it is now. I just need some direction. Mark pointed me towards the power supply circuit first after I started to replace transistors followed by some voltage readings and I tend to agree. Get power sorted and hopefully things will fall into place. Guess all I need now are thoughts on those resistors and opinions on what to do next.
And if you're still with me after this long post, thank you!
I decided to go ahead and replace Q1-10 on the Power Amp Assembly (AWH-033) after reading 2SC1451 and 2SA726 are problematic. This has been done and everything checked out with the DBT. However, while looking at the diagram of this board, I noticed two resistors that are on the diagram but not in my board. Specifically R17 and R18. Both are marked as 15K on the diagram. There is an indication on the silk screen as to where they go. On the bottom/foil side, there is solder there, but no indication that these resistors were ever installed. AK member Motnick, theorized that as mine is a '75 model and his a '74, there may have been a revision and those were taken out of mine. I'm not sure if this is any way critical to this board. I asked Mark about it and he suggested I post this on the forum and ask everyone. It doesn't seem to be an issue, unless this is what the origin of my crackle/pop turns out to be.
After replacing the transistors mentioned above, I'm still getting out of spec voltage readings on this board. (AWH-033)
Pin 6: 32.7
Pin 10: -13
Pin 33: 26.3
Pin 28: -26.3
Pin 29: -26.3
Pin 25: -26.3
Pin 22: 26.3
I was able to get 3 and 17 to 0 and 1(2) and 18(19) to 20mV as per manual and corrected instructions from the forum.
I suspect my voltage issue will be originating from the Power Supply Circuit Assembly.
(AWR-057)
Pin 14: 32.6
Pin 15: 28.4
Pin 16: 28.4
Pin 17: 21.3
Pin 19: 13.6
Pin 20: 13.6
Pin 21: 13.6
Pin 12: -13
Pin 13: -13
Pin 7: -27.5
Pin 10: -26.3
Pin 9: 26.3
I'm thinking I'll have to recap AWR-057 and subsequently other boards. I've kept up with Motnick's rebuild and I'm taking that as some inspiration to get this thing working better than it is now. I just need some direction. Mark pointed me towards the power supply circuit first after I started to replace transistors followed by some voltage readings and I tend to agree. Get power sorted and hopefully things will fall into place. Guess all I need now are thoughts on those resistors and opinions on what to do next.
And if you're still with me after this long post, thank you!