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Old 9th December 2008, 06:52 PM   #1
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Default Repairing a PPI PC6600.2

Amp repair virgin here… Picked up this PPI PC6600.2 and tested in my car using a 10 amp fuse. The amp cycled on and off every few seconds. There was a very limited amount of output and it was heavily distorted. The protection light did not come on. I really wanted to run this baby in my car as I could never afford any of the Art or PC series amps when they were new and because the 2 Xtant 403a's that I'm currently running take up a whole lot of space!

Before I found this forum or Perry’s site I opened the amp and found that there was a 7915ct that was scorched, so I ordered one and replaced it. I reassembled the amp and tested it again and there was no difference.

That’s when I started searching google and found BCAE1 and this forum… So far, I’ve found one output transistor that is shorted Q116 (2N6488) and the emitter resistor attached to it R222 looks a little burnt.

When attempting to measure pins 2 and 3 of output transistors my meter keeps giving me the 0L display so I measured pins 1 and 3 (ohms) of each output (both 6488 and 6491) and found 99 to 100 ohms on each except for the area of the board where there was obvious damage. This is where I found the shorted Q116. I removed and rechecked the output transistor and confirmed that it is definitely bad. I also lifted one side of the burnt looking resistor off of the board and tested it and it is open.


Everything that I’ve done so far I found by searching the forum but now I’m not really sure what I should do next and what parts I should order, besides the defective parts.

Should I replace all of the output transistors or just in the section of the amp were the damage was most evident?

thanks!

KC
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Old 9th December 2008, 07:54 PM   #2
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Location: Louisiana
You may have a defective driver transistor (was that Q116). For each channel, there are ~10 transistors near the emitter resistors. You need to check all of them in the defective channel. There is a driver transistor for each output. The driver transistor for the output that failed is almost certainly defective. Pull it and check it first. If there are no other problems, the amp should power up normally with a single output out of the circuit.

Remember, you MUST monitor the temperature of ALL of the heatsink mounted components if you're working on the amp with no clamps on the transistors/regulators.

You should replace all of the output transistors in that channel. You should also replace two of the emitter resistors (the one that opened and the one that is connected to the transistor with the same part number as the transistor that failed).

Do you have plus/minus rail voltage on the outputs?

Do you have plus/minus regulated 15v on the op-amps?
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Old 9th December 2008, 10:04 PM   #3
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Perry,

Pardon my ignorance... but I'm not sure which is the driver transistor for this channel????

Here are two pics of the board:

http://i197.photobucket.com/albums/a...W2002/ppi2.jpg

http://i197.photobucket.com/albums/a...W2002/ppi1.jpg

I have yet to hook the amp up to a power supply, not sure I want to let anymore smoke out yet. I have a decent CC/CV Kepco supply that I used to use for some electroplating but I need to dig out and figure how to get it set up properly first.

thanks for the help!

KC
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Old 9th December 2008, 10:11 PM   #4
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Q104? It's directly in front of Q116.

When you do power it up, do so with a 10-15 amp fuse in the B+ line. It would be best if you have the cover on and tightened down. If it doesn't draw excessive current, it would be relatively safe to operate it without the cover (short term - if needed for further troubleshooting). If it works correctly with the driver and Q116 removed from the circuit, order the replacement parts.

I thought it used 4 outputs per channel. It uses 6. You would need to replace 3 emitter resistors and 6 outputs. I'd also replace all 3 drivers for the 6488s.
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Old 9th December 2008, 11:11 PM   #5
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Its alive!!!!

I removed the driver transistor and popped the bottom back on and ran out to the car to give the amp a quick test run. Using a 10 amp fuse, It is working properly with no distortion in all six channels.

I'm slightly confused (nothing new there...) about the 6 outputs I should replace. I know I need to replace Q114, Q115 and Q116 (6488's)and the corresponding drivers and emitter resistors but what other do I need to replace?

thanks for you patience and spoon feeding!

KC
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Old 9th December 2008, 11:28 PM   #6
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The other 3 outputs in the channel, (6491s - Q118, 119, 120).
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