Pioneer SX-3900 Large Capacitors Bleed

[cferry1]

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

 

[rcs16]

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.

 

[mustang1102]

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.

 

[markthefixer]

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.

 

[mustang1102]

The math is ohm's law. voltage squared divided by resistance is the power being dissipated.

Thank you Mark. Will have to break out the Ohms Law circle and do some studying.

 

[tyttuut]

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.