SX-1010 question about transformer & voltages

tschanrm

New Member
I;ve got an sx-1010 a couple months ago. Last nice I checked some voltage measurements inside the unit to see how much work needs to be done besides new caps. Can anyone with a sx-1010 service manual tell me all the dc voltages I should be seeing after rectification? I'm only asking because some of these values seem off. For the main amplifier board, the secondary transformer windings give 40.1 vac, but after rectification its only + 52 and -52 volts or so. Shouldn't this be higher, like around 56v after rectification, or were diodes less efficient back then? Any help would be appreciated. :)
 
I'm not sure where you're measuring the AC voltage, but unless you have a pretty accurate true-RMS meter, you might not be seeing what you think you're seeing.

Measure the DC voltage right on the big filter caps...the manual calls for +/-56V. In my own experiance with 1010's, this is on the low side of what you should really encounter (typical is around +/-58 or 59V) unless you have low line voltage in your house, or unless your meter is bOrked. :scratch2:

As far as losses, the large diode assemblies used in some of the big Pioneer units are about the same as others...ought to be nothing unusual here.
 
My meter goes down to .01mv or so, and I've tested it out on other power sources and found it to be accurate, so I know its not my testing equipment. It reads 40.1 before the diodes and like 52v after rectification. My line voltage sits right around 114 vac. Sorry, I haven't tested it at the filter caps, but I will do so later.

Measure the DC voltage right on the big filter caps..

I thought it was be better to meaure voltage right after the diodes, rather than at the filter caps, as this would give a better indication of the actual voltage? The 52v i got was right before it left the board with all the slow blow fuses. Anyways, I inspected them closer tonight and noticed one the diodes has a golden film around the top of it, where the grounding bridge or whatever that dual package diode metal plate is. Could it be that one of the diodes in the bridge is bad? If so, what makes a proper replacement? I would think any standard 35a 200v bridge or soft recovery fast switching diodes would do just fine. Thank you for the info echowars.
 
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The output stages get their voltage from the caps, and when measuring so should you. ;) Plus, it's easy to get to.

In all honesty, it likely makes little difference, but if you measure at the caps you are certain to avoid any mistakes.

Those diode assemblies such as used in these old Pioneer's are pretty bulletproof. I've never seen one fail, but that doesn't mean it can't happen. I'd be more prone to think that your line voltage is low. Follow the power cord into the unit and carefully measure the AC voltage coming into the receiver. I'll bet you're under 110V.
 
I checked right out of an outlet socket, and right after the back fuse on the 1010, both read about 121 vac. I double checked the transformer, it still reads right around 40vac. I checked right after the rectifier, still around 52v. I checked at the filter caps, still around 52v. :confused:

Thanks for the help echowars; it seems the only cause for the low voltage is due to the rectifier, unless there is a way I can test my meter for inaccuracy. Besides, diodes are cheap, the only hard part will be figuring out how to solder them into place of the old ones.
 
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The most likely problem is the capacitors themselves. I'd replace 'em if you are getting a reading that low. Michael Percy sells a 22,000µf Nichicon cap that is the same diameter (so you can use the stock mounting bracket) but about 20mm longer. There is plenty of room, and I've made the swap three or four times.
 
tschanrm said:
I;ve got an sx-1010 a couple months ago. Last nice I checked some voltage measurements inside the unit to see how much work needs to be done besides new caps. Can anyone with a sx-1010 service manual tell me all the dc voltages I should be seeing after rectification? I'm only asking because some of these values seem off. For the main amplifier board, the secondary transformer windings give 40.1 vac, but after rectification its only + 52 and -52 volts or so. Shouldn't this be higher, like around 56v after rectification, or were diodes less efficient back then? Any help would be appreciated. :)
Welcome to AudioKarma! As you can see from my signature, a SX-1010 is one of the afflictions I've gotten after joining AK. Drop me a pm if you'd like to have a copy of the service manual. Good luck with your SX-1010!

- Harald
 
I ordered, and installed some of the Adcom 22000uF you see on Ebay into my Pioneer SX-1250. They are about 2 1/2 inches wide, 4.5 inches tall. They fit perfect into a SX1250, the screw terminals are short post, instead of the original long post, still, the metal bar clears the chassis, the screws themselves are a tad bigger. Yeah, I know its a different model than the 1010, but they might work for you. I cut a deal directly with the Ebay seller, he shipped me 4 for 80.00 total. You can't beat that price.They are probably not as good as the Nichicon Gold Series, but they are power supply caps made by or for Adcom.
 
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