Pioneer SX-9000 Blows Left 3A fuse. Help Please!

daveyh

daveyh

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I have tried to search the forum and find the answer to this but to no avail.

I have a Pioneer SX-9000 that blows the left 3A fuse in back and I can not for the life of me find the short. I thought it was in the amp board or output section but it must not be. Either that or I am missing something.

I have it powered on a DBT and the 100w lamp is bright with a new left 3A fuse in. When I pull that fuse out and leave the R 3A fuse in and power it up the lamp goes out and it works fine in the right channel.

Here is what I have done in my shotgun approach..

1. I pulled the outputs and checked them and all have checked out to be good on both sides. I installed new insulators and put them back in and still have a short.

2. I rebuilt the amplifier board with new transistors and recapped it. Still have a short.

3. While I was in there I rebuilt the power supply board. Still have a short.

I don't what to keep working on this anymore without some guidance on where to go next.

I know other people have had this same problem but when I search half the post is missing like it has been deleted?

Anyone have experience that would like to help me tackle this problem?
 
Pete, I replaced all the transistors in the driver amp board as well as the capacitors. I also pulled and checked the STV-3 diodes. They checked fine.

Yes I do have speakers connected to the speaker terminals.

I have also cleaned and works the VR3 and VR4 pots. Set them back the way they were.
 
try no speaker on bad channel ..if still bad look for physical shorting .
do you have history from before it started blowing the fuse ?
you could try disconnecting the output cap c3 to narrow things down .
 
Check to see if there are any shorts from the outputs to the heatsinks. I've seen burrs in the screw holes, cracks in the mica insulators, and leads touching the holes from worn TO-3 sockets. Also, with dim bulb check the voltages from base to emitters (the two leads coming out of the output transistors, Try using a smaller bulb to limit current even further until you track down the short.ne more idea - get voltages with no outputs installed. Good luck..
 
Last edited:
petehall347 said:
try no speaker on bad channel ..if still bad look for physical shorting .
do you have history from before it started blowing the fuse ?
you could try disconnecting the output cap c3 to narrow things down .
Click to expand...

OK. I will disconnect the speaker load and see what happens.

No I don't have history on the unit before it started blowing the fuse.

sregor said:
Check to see if there are any shorts from the outputs to the heatsinks. I've seen burrs in the screw holes, cracks in the mica insulators, and leads touching the holes from worn TO-3 sockets. Also, with dim bulb check the voltages from base to emitters (the two leads coming out of the output transistors, Try using a smaller bulb to limit current even further until you track down the short. Good luck..
Click to expand...

I did install new insulators when I put the outputs back in. All the sockets looked good. I will us a smaller bulb as see if it will power up.
 
Disconnected the speaker load and still have a short.

By disconnecting output C3 cap how would that help? Do you think it could be bad? None of the large caps show any signs of leakage.
 
Tried a smaller lamp in the DBT and it only makes the lamp flash on and off when turned on.
 
removing c3 would cut out switches and wiring going to the speaker .
see if there is any continuity from outputs to heat-sink . might be a bad insulator on a screw .
 
Well I removed the wires going to C3 and plugged in the unit to the DBT and the lamp is still bright. Dang!

No continuity from out pins to heat-sink.
 
daveyh said:
Pete, I replaced all the transistors in the driver amp board as well as the capacitors. I also pulled and checked the STV-3 diodes. They checked fine.

Yes I do have speakers connected to the speaker terminals.

I have also cleaned and works the VR3 and VR4 pots. Set them back the way they were.
Click to expand...
vr4 is right channel bias pot .
vr1 is left channel centre voltage pot . vr3 is left channel bias pot .
 
I tried removing the outputs on the one channel and it fried R29 (150) resistor.
 
check bias pot vr3 and make sure all transistors are the correct ones and inserted correctly in the board .
 
Double checked all the transistors. Before I installed them I installed them one by one on the right channel and powered it up after each one was installed. They all worked fine in the right channel. I did the same in the left channel double checking the orientation. I still has the same short after I installed them. I also pulled and checked the VR3 to make sure it adjusted. I also measured the inter and out solder points of both VR3 and VR4 pots and they are the same voltage.

If I pull the left channel 3A fuse and leave the right channel 3A fuse in the bulb goes dim and I can hear the left channel working but it is very distorted.
 
I have an SX-6000 that acted this way.

I went around and around in circles for a long time.
The STV-3 was bad. It tested OK but it wasn't.

I have also chased this issue where a resistor was bad.

SO.
Verify every resistor on the bad side, use the good side and just go side to side in circuit. This "can" fail if the actual solder joint or trace is bad and you don't catch it.
Then, swap STV-3 side to side to make sure its not that situation.
 
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