Pioneer SX-3900 Large Capacitors Bleed

cferry1

Active Member
Pioneer SX-3900

Rectifier Assy. AWR-211
Power Amp Assy. AWR-097

I never see the 60 volts supplied from the Main Transformer and rectified on the Rectifier Assembly Board dissipate after turning unit off. Never diminishes.
The very large ( 15000 uF ) filter electrolytic capacitors C3 and C4 never let go of their charge on this supply voltage.

I do not understand what circuitry / component (s) are responsible for bleeding this voltage once the unit is powered off.
My unit never bleeds this voltage down ( ???)

Any suggestions.

cferry1
 
They did not use any bleed resistors, which is a safety issue. You can put ~ 6800 ohm resistors across the big ecaps (60*60)/6800=0.53W, use 1W
They used 18K,1/2W on the SX-D7000, using the exact same transformer, go figure, cost savings for 2 resistors.
 
They did not use any bleed resistors, which is a safety issue. You can put ~ 6800 ohm resistors across the big ecaps (60*60)/6800=0.53W, use 1W
They used 18K,1/2W on the SX-D7000, using the exact same transformer, go figure, cost savings for 2 resistors.
Would you mind taking a minute and explain the math....it's been a long time since I had to think that hard. Also, how did you arrive at the 6800 value ? Thanks.
 
The math is ohm's law. voltage squared divided by resistance is the power being dissipated.

6800 ohms is a standard resistance value.

Less resistance = more heat and faster discharge times.

I thought his choice was a NICE compromise between power dissipation and discharge time.
 
I used some 10K 1 watt resistors to discharge the caps when I was working on my amp. At that value, the current flow with the unit on is negligible. You could probably go for a lower value. Like Mark said, 6.8k would work, but you need at least a 1/2 watt resistor, preferably 1 watt. If you went down to, say, 4.7k, you need at least a 1 watt resistor.
 
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