pioneer sa-6500 ii blown fuse

1968vwbug · 13th June 2010, 01:30 PM

Hi, I have a Pioneer SA-6500II and the two fuses next to the transformer and near the 2 large caps keep blowing up. I also noticed that one resistor (4.6 ohms) near the first transistor ( I guess it's a transistor as it has 3 legs) that is screwed onto the heat sink is burnt. If I replace that resistor, do you think it would stop blowing the fuses and start working? Thanks for your help.

llwhtt · 13th June 2010, 03:25 PM

Resistors don't go bad on their own. A bad resistor means that there was too much current flowing thru it and whatever is causing the current to flow, bad transistor(s), maybe (probably), is going to be your problem. You can change fuses all day long and each time you do could be making the problem worse especially if you try bigger fuses as many people do. The amplifier is broken and needs service. Do you have a schematic and what experience do you have with electronics? Test equipment?

Craig

1968vwbug · 15th June 2010, 03:31 PM

Maybe I'll just have my co-worker look at it. He is an electrical engineer and has all the test equipment. I did not want to bother him if it was only replacing the resistor.

I do remember that I used it once and there was no sound so I turned up the volume almost half way and that's when I noticed smoke come out.

Then I noticed that the speaker wires came unplugged. Maybe because I moved the entertainment center. Could this have happened because there were no speakers plugged in and I turned up the volume?

Thanks

llwhtt · 15th June 2010, 04:10 PM

Solid state amps "usually" don't care about having a load or speaker connected or not, tube amps on the other hand care very much.

Craig

kevinkr · 15th June 2010, 04:14 PM

This amp is probably over 30yrs old at this point and is a candidate for a full recap during the course of the repairs.

jaycee · 15th June 2010, 05:54 PM

I would bet good money that the wires only partially came out and have shorted the speaker outputs. This is going to be an "expert" repair job.

djk · 16th June 2010, 09:39 AM

The 4R7 burnt resistor is probably in series with the base of one of the outputs.

The outputs will be fried, and the drivers will also be fried. The emitter resistors for the outputs may be open, and the bias circuit may be damaged.

13th June 2010, 01:30 PM	#1
1968vwbug diyAudio Member Join Date: Jun 2010	pioneer sa-6500 ii blown fuse Hi, I have a Pioneer SA-6500II and the two fuses next to the transformer and near the 2 large caps keep blowing up. I also noticed that one resistor (4.6 ohms) near the first transistor ( I guess it's a transistor as it has 3 legs) that is screwed onto the heat sink is burnt. If I replace that resistor, do you think it would stop blowing the fuses and start working? Thanks for your help.

15th June 2010, 04:14 PM	#5
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	This amp is probably over 30yrs old at this point and is a candidate for a full recap during the course of the repairs. __________________ www.kta-hifi.net

16th June 2010, 09:39 AM	#7
djk diyAudio Member Join Date: Feb 2001 Location: USA	The 4R7 burnt resistor is probably in series with the base of one of the outputs. The outputs will be fried, and the drivers will also be fried. The emitter resistors for the outputs may be open, and the bias circuit may be damaged. __________________ Candidates for the Darwin Award should not read this author.

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13th June 2010, 03:25 PM	#2
llwhtt diyAudio Member Join Date: Jun 2008	Resistors don't go bad on their own. A bad resistor means that there was too much current flowing thru it and whatever is causing the current to flow, bad transistor(s), maybe (probably), is going to be your problem. You can change fuses all day long and each time you do could be making the problem worse especially if you try bigger fuses as many people do. The amplifier is broken and needs service. Do you have a schematic and what experience do you have with electronics? Test equipment? Craig

15th June 2010, 03:31 PM	#3
1968vwbug diyAudio Member Join Date: Jun 2010	Maybe I'll just have my co-worker look at it. He is an electrical engineer and has all the test equipment. I did not want to bother him if it was only replacing the resistor. I do remember that I used it once and there was no sound so I turned up the volume almost half way and that's when I noticed smoke come out. Then I noticed that the speaker wires came unplugged. Maybe because I moved the entertainment center. Could this have happened because there were no speakers plugged in and I turned up the volume? Thanks

15th June 2010, 04:10 PM	#4
llwhtt diyAudio Member Join Date: Jun 2008	Solid state amps "usually" don't care about having a load or speaker connected or not, tube amps on the other hand care very much. Craig

15th June 2010, 05:54 PM	#6
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	I would bet good money that the wires only partially came out and have shorted the speaker outputs. This is going to be an "expert" repair job.

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