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Old 28th July 2013, 07:57 PM   #1
neela30 is offline neela30  United States
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Default Punch 150s/Power 550s

Both of these amps are 2002 models which are old but definitely not "old school". I purchased them new years ago and ended up blowing both. They have collected dust for quite some time.

I just wanted opinions as to whether or not these are worth the time and effort to repair? The problem may just be in the thermal overload protection? They were not catastrophic failures, as the internals "look" fine and did not pop the in-line fuses if i remember correctly.
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Old 28th July 2013, 09:27 PM   #2
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Thermal overloads reset themselves. Your amps are damaged most likely. I can't attest to value of repairing your amps. Its generally something you either want to do, or not.

If there are no visibly damaged components it likely means the protection circuitry shut down the amp before any smoke letting occurred. This means you will have to meter out components till you find the issues and correct them. try ohming out the power devices attached to the heat sink. Generally speaking they tend to short out when they fail...hope this helps some.

Last edited by 1moreamp; 28th July 2013 at 09:41 PM.
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Old 28th July 2013, 10:16 PM   #3
neela30 is offline neela30  United States
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Thanks for the reply! I'll start checking for shorts and see what i find. If the repair appears to be fairly simple, I may make my first amp repair(s)! I have missed having a good sounding system...
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Old 29th July 2013, 05:54 PM   #4
neela30 is offline neela30  United States
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I decided to take a better look at the 150 and removed the boards for a closer look. I found heat discoloration around 2 resistors at the bottom right of the board.

2013-07-29 12.47.02.jpg

2013-07-29 12.47.55.jpg

2013-07-29 12.48.05.jpg

The resistors are in-line with fets IRF540 and IRF9540 (which appear to be on the same channel) and test at 0.3 Ohms and are not passing voltage through on diode tests. I don't know anything about color codes so I have no idea where to begin.
I get a whopping 28.7 ohms on the "bad" 9540 and several thousand on the other. All other pairs seem to have nearly identical readings (with each other).
I am a complete novice so I don't know if I'm testing correctly.

Any ideas?

Last edited by neela30; 29th July 2013 at 06:03 PM. Reason: clarification
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Old 29th July 2013, 06:15 PM   #5
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Try Perry Babin's Tutorial links first:
Links >> Basic Car Audio Amp Repair * Basic Car Audio Electronics * New Site * Basic Switching Power Supply Design * Basic Computer Skills << Links


Your channels outputs are blown, and the darkened resistor is burnt. It connects to the shorted output. This is a MESHA board amp try the links above Perry has done all the work for you and put it all together in a easy read. You will need more then a simple hand held soldering iron to remove and replace those fets attached to the MESHA panel. There are several methods. Its just large scale SMD mounting, but it will require a large heat source to remove those safely and not damage the panel so it can be reused. RF used to sell the panels but that was a long time ago. You will likely need to repair the existing panel. I use a Hakko hot air reflow wand, others use mini torches. It will be a learning experience if your a novice like you say you are. Perhaps you might defer this repair to someone that has done it before, since you lack the tools and experience to do it. DO NOT tear the device off the panel. It will simply slid off once you have it heated enough. Careful at these temperatures a severe burn is very possibly...hence my reasoning that you might have an experienced tech repair this one.

PS oh and yes I have at least a couple dozen of these over the years. Your likely going to have damaged components further back on the board in that channel. The schematic is available from RF at this link: http://194.204.29.93/rockford/techlib/products.html

Last edited by 1moreamp; 29th July 2013 at 06:20 PM.
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Old 30th July 2013, 02:02 PM   #6
neela30 is offline neela30  United States
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Thanks for all the info!
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Old 27th August 2013, 01:39 PM   #7
neela30 is offline neela30  United States
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The output transistors were the only defective parts I could find in the 150. I ordered and replaced what I could find and (after sorting through my awful soldering job) the amp simply works. I didn't even replace the burnt resistor because I wasn't sure what wattage/size etc I should replace it with.

I tested each channel independently and then bridged and the amp barely gets warm after 20 to 30 minutes of running bass music. I even went so far as to run a signal generator at 40-45 Hz for a while.

If I remember correctly, I blew this amp while running it bridged into a 2 ohm load (far from recommended for this amp).

It seems like it was too easy to me. Could I be this lucky? I guess I'll move on to the 550 and hope for the same result...
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Old 27th August 2013, 03:19 PM   #8
neela30 is offline neela30  United States
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I'm not going to be so lucky with the 550 it seems. It trips my power supply with just a REM connection. A quick resistance check makes it appear as if all but one transistor in the right channel is blown. I may wait until I get better equipment before I tackle this one!
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Old 27th August 2013, 03:26 PM   #9
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It's likely that only 2 of the output transistors are shorted. Measure from leg 1 to leg 2 for all of the outputs that appear shorted. It's likely that one of each part number (540/9540) will read lower than the other 4. Remove those from the circuit and re-check the remaining FETs.
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Old 27th August 2013, 03:38 PM   #10
neela30 is offline neela30  United States
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You are correct as always! ! One each of the 540/9540 are showing ~2 ohm resistance.

What concerned me was the roughly 20 resistances on the others in the area. I assume I am getting these readings because of the failed resistors still in the circuit?

Thanks Perry!
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