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Hey all,

I was going to pull this amp apart to replace a noisy fan so I thought this would be another good AMP GUTS post.













While in there I noticed the electrolytic caps on the power supply output were swelling and about to blow. It appears one of them already popped. No surprise here. The amp has been in service for over 12 years. I wonder how much ripple there is on the supply rails now that the capacitors are failing.




To be continued

Ge0
 

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Might as well order more caps and tag it onto my fan order.

The caps that are in here are some cheaply made Korean brand I have never heard of. On top of the normal specs of capacity and operating voltage you need to also pay attention to operating temp range, life time rating, ripple current rating, and of course case size. With all of this info at hand I can order replacements from suppliers I know and have experience with like Nichicon and Kemet.







I have replacements on order. I'll update this post once they arrive.

Ge0
 

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I have the parts in and time on my hands to fix it. Here is where we left off:



I absolutely HATED these heat sink clamps. I tried A bunch of things to break them loose. I could not due it. Then, I watched a random youtube video from some SPL amp repair dude. He made it look so simple.


Take a tool, wedge it in the hole, then push down on the fulcrum as the inserted tip pushes up. With enough pressure the clip breaks free:







Now finish the rest like this. If you don't have clearance or have one that won't budge change tools.







Next, get out your 1/4" hex drive and remove 3 screws holding the PCB down:




At picture limit. More to come...

Ge0
 

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One you have released all the heat sink clamps and have removed all three 7/34" retraining screws + washers the main board will work itself out with a little manipulation:








Again. here are the sick and bloated caps we need to remove




And here is some heatsink crap that needs to be cleared off:



Fire up that old and crusty soldering iron. We are going to need a broad tip to do this job.










Picture limit again dammit...

Ge0
 

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My secret underground lair. Or, extremely messy utility room doubling as electronics lab








Prepping for surgery:






A lot of this procedure I had to do without pictures because it took both hands to work. To extract a capacitor heat both leads until the solder is obviously flowing. Then pull it out gently while continuing to apply heat. If your soldering iron only has a narrow tip then you can heat one lead at a time & pull up on it. With this method you essentially walk or wiggle the capacitor out. Remember, the caps are secured down with silicon too. You may need to cut the silicon before you can pull the cap out.



Look how bloated the bottom of this cap got. The fluid inside must have boiled:



The top of this cap blew and spewed electrolytic fluid onto the amps cover. The tabs were lifted up. I pushed them back down with my finger by accident when measuring them earlier.




Extract both caps and clean the remaining solder out of the hole with solder wick. next, clean excess flux from the area with rubbing alcohol or flux removal spray. Finally scrape away any silicon left on the solder pads :









Ge0
 

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Now you can install the new capacitors. Be careful here. I lifted a solder pad on the bottom side of the board while extracting my first cap. You'll need to solder these from the top side since the bottom solder land is gone. Simply load your soldering iron tip with solder, push the capacitors lead in the hole (watch and make sure the polarity is correct) and then heat the joint between the top side solder land and capacitor lead. Once the solder is hot and flowing you can push the capacitor in all the way. The solder will cool under the capacitor. The next lead you can solder from the bottom side like normal. The other lead will poke through the circuit board but there is no solder land to solder to. Put fresh solder on your irons tip and warm that lead up again. This will help reflow solder on the top side to make sure you do not have a cold solder joint. Unfortunately this is a cheap circuit board with light weight copper. You may end up lifting more than one solder land no matter how careful you are. Make sure to clean left over flux once done. Trim the leads right above the solder joint:



Much of this now is just rinse and repeat. All of the secondary caps either blew of were about to explode:



This one in particular really shit the bed. It spewed electrolytic fluid all over the board:












Gotta clean that mess up. Don't want to leave contamination behind on your circuit board. It could eventually attract nasties that create short circuits.



Now suck out the remaining solder out of the holes with solder wick, clean the area thoroughly, then install your new caps:



Don't forget to clear away left over solder flux when done. Deactivated solder flux is a corrosive that will attack the metals on your board:



The two electrolytic capacitors on the power supply primary didn't look too bad. However, since I was in here I decided to replace them as well to give the amp a fresh start. I didn't document this because it was identical to the others I've just shown.

Ge0
 

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Lol I hate those heat sink clips too ;). I have an even bigger allen wrench I use with the sides ground down, fits more snuggly and pops them off pretty easily.

What really sucks is if you mangle one, then you need to find a replacement.
 

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Before re-assembling the amp we need to clean off all the old heat sink compound and put fresh stuff on. Iso-propyl alcohol is perfect for this. You may want to scrape away larger chunks of dry stuff first before cleaning. Be patient and have plenty of paper towels handy. This is going to take a while. Be gentle, you don't want to bend transistor leads while cleaning.











I thought at first I would use the fancy heat sink compound I use on my computer CPU and GPU. However, I forgot this stuff only spreads well when heat activated. I could not spread it at room temperature with a q-tip. So, I went the more conventional route with normal heat sink compound. Remember, you just need a light coat over the transistors. Don't goop it on:





Now, insert the board back into the heat sink and re-place the heat sink clips. The smaller ones can be pressed back in by hand for the most part. If you can't do this with your thumb then a Phillips head screw driver will help. Just give the end a gentle tap with a hammer and the heat sink clips will pop right back in:









Ge0
 

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Now, finish assembling the PCB and make sure everything is secured. It may be a good idea to do a quick power-up before putting everything back together. Yep, amp comes out of protection mode. Green light means go and fans are spinning:











This is the noisy / howling fan:



Now, clip the leads on the old fans and solder them to the new ones:






Fans re-installed and ready to go






One of the toughest parts is to make sure all the indicator L.E.D's are aligned properly when putting the cover back on. They are easy to bend when handling the board:



Ge0
 

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OK. Got the lid on tight. Let's power this sucker up and put the juice to it









Need to use my old test mule. Can't seem to find my box of 500W load resistors. Trust me, these things are large. How could I misplace them? Each one is about the size of a shoe
. Well, we won't be testing the amp to full load today. But, we can give it a good burn in within the 300W limit of the sub.



Signal generator maxed out at 20V and only applying about 130W to the sub.



The jumper settings are too high on my high level input converter. I don't feel like digging out the manual to make the proper jumper connections. It's easier to just switch over to the line level converter:








There we go. 30Hz at 9.8V input is giving 300W output. I purposely set my current limit at 30A to protect the sub. Its only rated for 300W. So, ran the amp at 10V and 30A for an hour to burn it in and test it. Fans ramp up and down properly under heavy load. But, most of all they are whisper quiet. If you remember, this was the entire reason I started this exercise in the first place. A noisy / dying fan. Well, mission accomplished...

Ge0
 

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Lol I hate those heat sink clips too ;). I have an even bigger allen wrench I use with the sides ground down, fits more snuggly and pops them off pretty easily.

What really sucks is if you mangle one, then you need to find a replacement.
I'll bet. Fortunately I didn't have to go there :). I've repaired close to 100 amps. This is my first bought with this type of heat sink clip. Fortunately, big bulky heat sinks and massive clamping mechanisms are a dying breed. If you get a chance, look at my evaluation of my stock Bose amplifiers out of my latest car. This is where modern tech is heading.

Geo
 
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