Hey fine people of the Adiokarma community,
I’m rather new at this, but picked up a non-working SX-1010 and decided (based on all the stellar reviews of this unit) that I’d try to figure out if I could get it working to be my home daily driver (I’ve recently caught the vintage audio bug). I don’t have a background in electronics repair, so go easy on me. I’m having some fun diy’n it as I like to tinker with stuff, but have run into some obstacles along the way. The unit, under initial inspection, had a lot of dust in it and showed some signs of moist storage in the past (there is some oxidation on the front bezel pieces). Everything cleaned up pretty good though and I’ll deal with cosmetics after I get the inners working up to snuff. The main fuses in the back (one standard and one slow blow) were both blown and one of the main power caps was leaking fluid. I started by replacing the fuses and the main caps, then powered it up on a DBT and the unit was shorting somewhere (bright bulb). Based on reading a bunch of posts on this excellent site, I decided to pull the output tranies, insulate the bases and see what that did. Powered it back up on the DBT and it lit up and faded as it should. I tested the output tranies and two were toast. I then ordered new output transistors and all the parts from the most current BOM based on the latest information I could find (MTF’s BOM). I thought if I’m replacing the outputs, I should also replace the recommended parts on the amp boards as they would be more accessible with the heatsinks removed. I did this (not without issues…. I messed up on some of the transistor lead placements on the amp board and smoked a resistor but got that fixed up. Got everything buttoned up, adjusted the pots and everything worked like a champ. I then felt pretty good about things…. enough so that I decided I should tackle the notorious power supply board with the parts listed in the BOM. This time, no issues with transistor lead placement but I did have a bad weld to one of cap leads that was causing a low voltage reading at one of the pins, but I found that and got it fixed. Buttoned that up and adjusted the pots on the amp boards again and it was running smooth again.
Now comes the issue that I’m looking for help with…. I next decided to take on the protection board…. so I replaced the parts listed in the BOM, powered it up on the DBT and it seemed to work the first couple of times (I didn’t leave it on for much time… on and off a couple of times) so I started buttoning things up and was powering it up again (still on DBT) to adjust the pots and the bulb stayed bright…..crap! I tried it one more time and the dim bulb now dimmed again so I thought maybe a loose wire or something, but I couldn’t adjust the idle current at all (it stayed at one value no matter how much I turned the pot – same approximate value on both left and right amp board). I figure that something got fried, so I’ve been trying to figure out where the problem is and in doing so, took readings from the pins on the power supply board:
1 = 55v ac
2 = 55v ac
3 = -35.7v dc
4 = -31.4v dc
5 = -29.1v dc
6 = 5.9v dc
7 = 0v dc
8 = 12.8v dc
9 = -12.9v dc
10 = -56.9v dc
11 = -23.6v dc
12 = 0v dc
13 = 36.7v dc
14 = -8.9v dc (this looks suspicious, should be 56v)
15 = 23.7v dc
As you can see, pin 14 voltage is pointing to the problem. Based on this, I looked around and noticed that R11 on the power supply board was fried. I replaced it and the same thing happened (DBT stayed bright), so I pulled R11 again (this is how it stands now). So currently my thinking is that something in circuit along power supply pin 14, which goes to amp boards pin 4 is the culprit. This is where it gets fuzzy for me and I am looking for some help. I don’t understand how the amp board works and I don’t want to create more problems than I have now.
I’m wondering if the issue is related to the fact that I didn’t turn the VR2 pots to the full counterclockwise position prior to power up on the dim bulb after doing the work on the protection assembly…. may have been too much current and blown something?
Any help in diagnosing this issue would be greatly appreciated. It really sounded great when it was working for the short time it did…. looking forward to getting it up and running again.
Thanks!
I’m rather new at this, but picked up a non-working SX-1010 and decided (based on all the stellar reviews of this unit) that I’d try to figure out if I could get it working to be my home daily driver (I’ve recently caught the vintage audio bug). I don’t have a background in electronics repair, so go easy on me. I’m having some fun diy’n it as I like to tinker with stuff, but have run into some obstacles along the way. The unit, under initial inspection, had a lot of dust in it and showed some signs of moist storage in the past (there is some oxidation on the front bezel pieces). Everything cleaned up pretty good though and I’ll deal with cosmetics after I get the inners working up to snuff. The main fuses in the back (one standard and one slow blow) were both blown and one of the main power caps was leaking fluid. I started by replacing the fuses and the main caps, then powered it up on a DBT and the unit was shorting somewhere (bright bulb). Based on reading a bunch of posts on this excellent site, I decided to pull the output tranies, insulate the bases and see what that did. Powered it back up on the DBT and it lit up and faded as it should. I tested the output tranies and two were toast. I then ordered new output transistors and all the parts from the most current BOM based on the latest information I could find (MTF’s BOM). I thought if I’m replacing the outputs, I should also replace the recommended parts on the amp boards as they would be more accessible with the heatsinks removed. I did this (not without issues…. I messed up on some of the transistor lead placements on the amp board and smoked a resistor but got that fixed up. Got everything buttoned up, adjusted the pots and everything worked like a champ. I then felt pretty good about things…. enough so that I decided I should tackle the notorious power supply board with the parts listed in the BOM. This time, no issues with transistor lead placement but I did have a bad weld to one of cap leads that was causing a low voltage reading at one of the pins, but I found that and got it fixed. Buttoned that up and adjusted the pots on the amp boards again and it was running smooth again.
Now comes the issue that I’m looking for help with…. I next decided to take on the protection board…. so I replaced the parts listed in the BOM, powered it up on the DBT and it seemed to work the first couple of times (I didn’t leave it on for much time… on and off a couple of times) so I started buttoning things up and was powering it up again (still on DBT) to adjust the pots and the bulb stayed bright…..crap! I tried it one more time and the dim bulb now dimmed again so I thought maybe a loose wire or something, but I couldn’t adjust the idle current at all (it stayed at one value no matter how much I turned the pot – same approximate value on both left and right amp board). I figure that something got fried, so I’ve been trying to figure out where the problem is and in doing so, took readings from the pins on the power supply board:
1 = 55v ac
2 = 55v ac
3 = -35.7v dc
4 = -31.4v dc
5 = -29.1v dc
6 = 5.9v dc
7 = 0v dc
8 = 12.8v dc
9 = -12.9v dc
10 = -56.9v dc
11 = -23.6v dc
12 = 0v dc
13 = 36.7v dc
14 = -8.9v dc (this looks suspicious, should be 56v)
15 = 23.7v dc
As you can see, pin 14 voltage is pointing to the problem. Based on this, I looked around and noticed that R11 on the power supply board was fried. I replaced it and the same thing happened (DBT stayed bright), so I pulled R11 again (this is how it stands now). So currently my thinking is that something in circuit along power supply pin 14, which goes to amp boards pin 4 is the culprit. This is where it gets fuzzy for me and I am looking for some help. I don’t understand how the amp board works and I don’t want to create more problems than I have now.
I’m wondering if the issue is related to the fact that I didn’t turn the VR2 pots to the full counterclockwise position prior to power up on the dim bulb after doing the work on the protection assembly…. may have been too much current and blown something?
Any help in diagnosing this issue would be greatly appreciated. It really sounded great when it was working for the short time it did…. looking forward to getting it up and running again.
Thanks!
