Onkyo TX-8511 Repair Help - AVS Forum
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post #1 of 7 Old 04-02-2010, 02:29 PM - Thread Starter
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Hey all. I thought I would cast about for some help where I am comfortable first. I am not an electronics repair tech but know my way around a soldering iron.

I was given a fried Onkyo TX-8511. The original owner told me that one day the mains fuse inside blew out on them. They replaced it but nothing happened after that.

I popped the hood. Their new mains fuse was fine. I gave the unit a general look over and didn't see anything obviously blown. All caps looked good. Ran the multimeter in a few spots to verify what I could. Best I could figure was that perhaps the main power supply had gone south. It didn't hum when plugged in, or warm up. The display on the front was completely dead. No relay clicks when plugged into the mains. The switched outlets on the back remained off.

During the course of general poking and prodding I pulled the entire front off the amp to get a better look around. This included pulling the white ribbon cable that connects the display and front controls to the main board.

Not having any luck I decided to wrap it up for the day, put everything back together, and "just in case" I jarred something, I plugged it back in.

Heard a relay click, something sizzle and then the main fuse popped all at the same time.

Turns out I had forgotten to plug the ribbon cable back in. When I did this it allowed something to power up and then promptly blow out the fuse. I tested this theory by putting another fuse in, putting the ribbon cable in place, and plugging her in. Nothing. Pulled the ribbon while live, and then the relay clicked, fuse blew, etc.

By smell and touch (warmth) I traced back to these guys:



Obviously the one on the left is not feeling too well. What is this? A regulator?

Here's an overhead shot of the guts, with the location of the (regulators or whatever they are) circled.



So my questions are these: assuming this regulator was already toast, could it be the source of the unit being dead? If so, do you they tend to take other components down with them?

If not, and the blown (regulator) is symptomatic of something else, any ideas what that could be? The power supply perhaps?

A shot in the dark I realize, but what the heck Thanks in advance for any help.
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post #2 of 7 Old 04-03-2010, 05:53 AM - Thread Starter
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Well, perhaps that component isn't broken. I found a picture of the part elsewhere and it looks identical.



Anyone have any ideas?
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post #3 of 7 Old 04-06-2010, 04:03 PM - Thread Starter
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...crickets...

Nothing? Bummer.
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post #4 of 7 Old 04-06-2010, 04:21 PM
 
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What does your multimeter tell you about the regulators?
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post #5 of 7 Old 04-06-2010, 04:24 PM - Thread Starter
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Thank you for your reply.

I'm not sure how to test them without running power through them, and when I do that (see above WRT the front panel ribbon cable), it (or they) starts to smoke.
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post #6 of 7 Old 04-06-2010, 05:42 PM
 
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From the left, pin 1 is the input, pin 2 is ground or some reference voltage, pin 3 is the output. Check resistance to ground from all 3, the in and out should be relatively high resistance. If there's a short in the circuit fed by the regulator, or the reg is shorted internally, you'll see it. Since the fuse that blows feeds the regulator, it looks like the fault is there. A good regulator would probably survive a short in the rest of the circuit and shut itself down.
If everything looks good, remove the regulator, apply power and see if the raw voltage is at the regulators input, if the fuse blows at least you've isolated the fault.
Is the power supply a transformer, rectifier, cap? or an SMPS?
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post #7 of 7 Old 04-07-2010, 06:46 AM - Thread Starter
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Thanks, I'll give that a go this weekend and see what I find.
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