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Old 31st January 2006, 01:53 AM   #1
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Default PPI Amp Problem - PC21400

Hello All,

First off, apologies for being a newb. I will try my best to describe the problem.

I have a PPI PC-21400 amp. When I bought it 2nd hand it did not work. It powered up but played intermittently and very low power with lots of distortion. I took the back plate off and found one of the wires coming from the big donut looking thing (wrapped in wires) was desoldered where it went into the board.

I got that fixed. No other parts appear burnt or broken. I hooked it up (still have back plate off to see inside) and it played perfectly. Then after about a minute I heard a faint high pitched whine. I thought it was the fan coming on, but the fan was not moving. If I turn the volume down very low the noise goes away in a few seconds. If I turn the head unit and amp off the noise goes away instantly. If I turn the volume to ~3 (on a scale of 1-10) the high pitched sound may come back after about 10 seconds. If I turn the volume up to ~7 the sound comes back immediately.

My thought, and please tell me if this sounds way off base, is that the fan is shot. The amp is trying to turn the fan on either due to heat or load, but it won't go. This is causing the noise (like when you stop an electric motor that still has current going to it). The fan blades spin fine by hand.

So if you think it is the fan, where do I get a replacement? If you think it is something else, please tell me where to look. Thanks!!

EVOlutionary

(BTW, I have 3 of these on eBay right now if anyone is interested)
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Old 31st January 2006, 04:05 AM   #2
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I believe that that model amp uses the bottom cover to clamp the transistors to the heatsnk. Operating it without the bottom cover clamped tightly down is risky. If the transistors are not making contact with the heatsink, they can overheat and fail within seconds.

To determine if the fan is being driven on, measure the voltage across the fan wires. The voltage will need to be ~5 volts (minimum) to get the fan to run.

I'd suggest that you reassemble the amp and run it until it gets hot to see if the fan runs.
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Old 31st January 2006, 04:37 AM   #3
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Thanks for the info! Hope I didn't do any more damage yet. How do I measure the voltage at the fan with the cover on, or should I just listen for the fan to start.

Also, what are the transistors? Are they all the little black things along the perimeter of the circuit board?

EVOlutionary
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Old 31st January 2006, 05:17 AM   #4
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If that amp has the same fan circuit as the 2600.2 that I have here, the amp will have to reach a relatively high temperature (approaching the point to where it's uncomfortable to hold your hand on it) to switch the fan on.

If you can install it in your vehicle and run it until it gets hot, you should be able to get the fan to switch on. It's a very quiet fan so it will not be easy to hear.

For the most part, the components along the edges of the board are transistors.
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Old 31st January 2006, 05:30 AM   #5
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Thanks again. Here is a quick picture of the internals.

EVOlutionary
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Old 5th February 2006, 03:42 PM   #6
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Default Re: PPI Amp Problem - PC21400

Quote:
Originally posted by EVOlutionary
Hello All,

First off, apologies for being a newb. I will try my best to describe the problem.

I have a PPI PC-21400 amp. When I bought it 2nd hand it did not work. It powered up but played intermittently and very low power with lots of distortion. I took the back plate off and found one of the wires coming from the big donut looking thing (wrapped in wires) was desoldered where it went into the board.

I got that fixed. No other parts appear burnt or broken. I hooked it up (still have back plate off to see inside) and it played perfectly. Then after about a minute I heard a faint high pitched whine. I thought it was the fan coming on, but the fan was not moving. If I turn the volume down very low the noise goes away in a few seconds. If I turn the head unit and amp off the noise goes away instantly. If I turn the volume to ~3 (on a scale of 1-10) the high pitched sound may come back after about 10 seconds. If I turn the volume up to ~7 the sound comes back immediately.

My thought, and please tell me if this sounds way off base, is that the fan is shot. The amp is trying to turn the fan on either due to heat or load, but it won't go. This is causing the noise (like when you stop an electric motor that still has current going to it). The fan blades spin fine by hand.

So if you think it is the fan, where do I get a replacement? If you think it is something else, please tell me where to look. Thanks!!

EVOlutionary

(BTW, I have 3 of these on eBay right now if anyone is interested)
Whoa!!!! Perry is correct about the backplate being used to clamp the 'hangoffs' to the heatsink. It has been many years since I worked on one of those amps, but I know you NEVER run the amp under load without the backplate. We ahd to use RTV to hold the inductor in place. Sometimes we got returns where there was very little RTV and the inductor just vibrated loose.

If you run the amp loaded, without the backplate, first you run the risk of the + and - 15V regulators running-away(thermally). Next the switchers. If you are hearing a whining noise, it is because the bias is off, which is a result of non-symmetrical DC rails.

The fan is the last thing you should be worried about at this point.
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