Troubleshooting Pioneer S-W700 subwoofer

Thread Starter

fordman76

Joined Mar 30, 2022
84
I am rusty with troubleshooting skills, so I am having a difficult time finding the issue with my Pioneer S-W700 subwoofer. I have tried to determine what is causing the unit to blow fuses as soon as power is applied. So where do I star? All I have is a multimeter to aid in troubleshooting. I think there is a short somewhere causing the fuse to blow. Can someone tell me where to start? I have the schematic, but need a method and starting point for troubleshooting. Please help!
 

MrChips

Joined Oct 2, 2009
26,133
The first place to start is to find the Service Manual or at least the circuit schematic.

Circuit-wise, look for a short across the power rails followed by shorted output power transistors.
 

Thread Starter

fordman76

Joined Mar 30, 2022
84
Thanks Mr. Chips. That was helpful. Using my fluke multimeter, I tried measuring the 2 pair output transistors, 2SA1264N and 2SC3181N in circuit. I don't get typical readings for NPN or PNP bipolar transistors Typical measurement 14 ohms base to emitter with red lead on the base and black lead on the emitter. 0 .4 with red lead on the base and black lead on the collector. Reversing the leads I get 220 ohms and 235 with leads reversed. Same on both 1st channel pair. 2nd channel pair B to E = 0.7,, B to C= 0.7, second one B to E =0.5, B to C=0.5. Reversing the leads give me same readings.

How do I find shorts across the power rails?
 

Thread Starter

fordman76

Joined Mar 30, 2022
84
No problem. I just appreciate you looking at them and offering your expertise. No rush. I understand this is your time. I used to do a little TV repair some 25 years ago. Lost interest in audio/video until recently. Being forced to spend a lot of time indoors due to the pandemic, brought a lot of vintage audio equipment in my possesion, to my mind. I have this subwoofer, some old Infinity speakers, a Sansui 7070 receiver and a few other pieces to work on.
 

Thread Starter

fordman76

Joined Mar 30, 2022
84
I will check on the modules. I will venture to Home Depot tomorrow to pickup peices to build this test jig. What wattage bulb, 100 watts?
 

Thread Starter

fordman76

Joined Mar 30, 2022
84
Got the jig made and working. Checked it a few minutes ago with the subwoofer plugged in. It did not blow fuse. The modules looks like they are soldered.
 

Thread Starter

fordman76

Joined Mar 30, 2022
84
Looks like there is a cable from the front assembly( module 1) to the power assembly board . Looks like it's glued with some type of white glue. The cable from the power board to module(2)looks like it can be disconnected.
 

MrChips

Joined Oct 2, 2009
26,133
Ok, thanks for this.
With the unit turned on, can you describe the intensity of the 100W lightbulb in the test jig?
i.e. very dim, dim, medium bright, very bright.
 
Top