# Help identifying a US Amps?



## Dawgless (Oct 6, 2014)

Anyone happen to know what this model number might be? I was thinking a 442, but i know that's not right. Maybe a 425? 

Anyone happen to know what the two switches might be for?


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## ATOMICTECH62 (Jan 24, 2009)

It has the same style heat sink as the 50hca,200hca and 500a so maybe a 425a?


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## OldSchoolAddict (Sep 23, 2014)

Pull it apart and read on the solder side of the board. It'll say what model it is and all that. 

Don't be a wuss, its fun. Takes 10 minutes


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## Dawgless (Oct 6, 2014)

OldSchoolAddict said:


> Pull it apart and read on the solder side of the board. It'll say what model it is and all that.
> 
> Don't be a wuss, its fun. Takes 10 minutes


Haha!! 

Yeah, gonna have to tear it down now. I powered it up to test each channel and ended up getting only one channel to work correctly. One one side, there was some "cross-talk" between inputs and outputs. Seemed kinda weird. Also, volume was way off. For a period, one output was as normal, but then went quiet. 

If you look closely, there are three, if not four burned resistors. I'll have to get those replaced, along with all the caps. Just like you heard, one of mine was making a weird sound when powering up. 

Oh well!! The resistors and caps are easy to replace!! No overheated FETs, so I think those are all good.

Oh, and the switches are for full pass and low pass only. 

ATOMICTECH62, I also guessed at it being a 425a. Not much out there on these old ones. Thinking this is a relatively rare piece.


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## OldSchoolAddict (Sep 23, 2014)

Very nice, I really like the color (couldn't see the pics earlier lol
)


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## ATOMICTECH62 (Jan 24, 2009)

The strangest thing about that amp is all the surface mount devices for the crossover and driver section for each channel.Ive never notice a U.S. to use SMD's.
Being that its so old I would never expect that.The board had to run through a Flow solder machine before the other parts where added.


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## Dawgless (Oct 6, 2014)

Interesting. That's good to know ATOMICTECH62. 

I'm going to try to get it torn down tonight. I'll see what's printed on the opposite side of the board. 

Gonna have to get the caps and the resistors replaced here soon, as well as testing all the FET's. I think I'm also going to replace all the power, ground, and speaker wiring with longer wires. What's there is fairly short, and I don't want a splice that close to the case.

But it was good to see her powered up and working! No smoke or anything out of her.


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## Dawgless (Oct 6, 2014)

Guess what?

Pulled the board tonight.

Here's the bottom side!

really crappy panoramic shot with my iPhone


And more closely:


Alas! The secret revealed. time to get some resistors and caps replaced and see if she'll work!


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## vwguy383 (Dec 4, 2008)

Glad you figured it out. Is there any concern with those traces? The wide ones that look like they r lifting? Not an expert, but maybe someone can chime in on that.



Alas! The secret revealed. time to get some resistors and caps replaced and see if she'll work!QUOTE=Dawgless;2205800]Guess what?

Pulled the board tonight.

Here's the bottom side!



And more closely:
 [/QUOTE]


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## Dawgless (Oct 6, 2014)

Yeah, I tried pushing on the traces with my fingernail and they didn't feel like they were going to move at all. I'm guessing not an issue, but I'll wait to hear from a pro. 

There's four known bad resistors, of which I'll need to source and replace. Also, I'm going to replace all the caps. Once that's all done, I'll also go through and check all the FET's to ensure they're all good. The speaker, power, and ground leads are all super short, so I'm also going to solder in new ones to ensure there are no issues with installation. I'd like at least 24 inches of exposed wiring to give me room to space it away from my fuse-block.


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## ATOMICTECH62 (Jan 24, 2009)

Its not that they are lifting,its just wrinkles from the manufacturing process.
Think of it as if you took a sheet of aluminum foil,wadded it up,then spread it out flat again.
I see this on almost all higher end made in the USA boards.

Out of curiosity I just tried to push one of the wrinkles down flat on an old Zed made Autotek to no avail.Im thinking there must be something like glue bubbles under them.

EDIT
Disregard everything I said.I just took a wiz wheel to one and it is sold material all the way to the board.
All these years of wondering about this and it took 30 seconds to find out the truth.
I learned something new today.


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## Dawgless (Oct 6, 2014)

ATOMICTECH62 said:


> Its not that they are lifting,its just wrinkles from the manufacturing process.
> Think of it as if you took a sheet of aluminum foil,wadded it up,then spread it out flat again.
> I see this on almost all higher end made in the USA boards.
> 
> ...


Hot damn! The pros have spoken and it is good. I guess I'm not going to worry about it. All the small traces look good. 

ATOMICTECH62, if you can look at the top of the board in the earlier pictures, and I know it's hard to estimate from just a picture, but would you think the smaller green resistors(the ones that are clearly burnt in the pictures) are around a 1/2w? I tried doing some research, and have yet to fully complete it, but I think this was initially what I was coming up with. I looked at the bands a bit more closely and it goes brown, black, black, gold. I'll have to do all four green ones, then all the caps.


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## ATOMICTECH62 (Jan 24, 2009)

They do look like 1/2 watt resistors.But,if you dont want the new ones to do the same thing just get 1 watt replacements.If they are brown/black/black.gold then they are 10 ohm 5% tolerance.
Those resistors will be connected to the green caps.All the RC network does is shunt very high frequencies to ground.Mostly higher order harmonics.
These resistors will always show heat damage when the amp is driven into hard clipping.The square wave from this creates harmonic spikes at high voltage and all that energy goes through that resistor causing heat so they turn brown.A higher wattage resistor can shed more heat due to the increased surface area and will have a longer happy life.Hell,you could put a 5 watt resistor in its place but that would be over kill.
When ever I see these burnt in an amp I know some had the gain maxed out.
Poor amp.


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## Dawgless (Oct 6, 2014)

ATOMICTECH62 said:


> They do look like 1/2 watt resistors.But,if you dont want the new ones to do the same thing just get 1 watt replacements.If they are brown/black/black.gold then they are 10 ohm 5% tolerance.
> Those resistors will be connected to the green caps.All the RC network does is shunt very high frequencies to ground.Mostly higher order harmonics.
> These resistors will always show heat damage when the amp is driven into hard clipping.The square wave from this creates harmonic spikes at high voltage and all that energy goes through that resistor causing heat so they turn brown.A higher wattage resistor can shed more heat due to the increased surface area and will have a longer happy life.Hell,you could put a 5 watt resistor in its place but that would be over kill.
> When ever I see these burnt in an amp I know some had the gain maxed out.
> Poor amp.


Thank you for the info! I don't know enough about these to know that I could swap up for a higher wattage resistor. I guess as long as the resistance and tolerance are the same, what would it matter, right? There's adequate room to solder in a slightly larger resistor, so I'll go for it. 

I am curious, but would these being burnt have anything to do with diminished output from three of the four channels? When powered up the first time, two of the channels worked as normal, and two were basically non-existent. There was faint output. Then, one of the channels that was working properly went away to diminished output as well, but the weird thing is that there was some of what I would call "cross-talk" between two channels. 

The two channels with "cross-talk" are the ones on the left in this picture:


With the RCA hooked up to only one input, I was getting faint output on both channels on this side. The far right input was the only channel I got normal output on. Is there something I should be specifically checking for problems? I didn't have time last night to check each FET, but I'm guessing that maybe a handful of them are now bad?


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## ATOMICTECH62 (Jan 24, 2009)

Usually when you get crosstalk it has something to do with a signal ground.It will act like an ambiance kind of sound,low and hollow.
Maybe due to bad or dirty pots,RCA grounds maybe even crossover switches.
Those burnt resistors wouldn't have anything to do with the low output.


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## Dawgless (Oct 6, 2014)

Okay. Thanks! Yeah, the output was so low, I could barely hear it on my test speaker. 

I'll try to do some work this weekend and see what I can determine. It might be a while before I can get to work on the amp, lots of things going on in my life right now, but I'll report back on what I come up with. Your help has been immeasurable, thank you for the assistance!


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## TrickyRicky (Apr 5, 2009)

vwguy383 said:


> Glad you figured it out. Is there any concern with those traces? The wide ones that look like they r lifting? Not an expert, but maybe someone can chime in on that.


Solder wave process....those wrinkles/bubbles underneath the protective layer is perfectly normal.


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## ATOMICTECH62 (Jan 24, 2009)

Try putting about 10 drops of rubbing alcohol in each crossover switch,move them back and forth rapidly about 10 times.
That should be enough to remove any gunk and eliminate those switches from the equation.
It might even fix the problem if your lucky.Ive seen so many older amps like Soundstream and JBL that used crappy switches this was all it took.


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## Dawgless (Oct 6, 2014)

ATOMICTECH62 said:


> Try putting about 10 drops of rubbing alcohol in each crossover switch,move them back and forth rapidly about 10 times.
> That should be enough to remove any gunk and eliminate those switches from the equation.
> It might even fix the problem if your lucky.Ive seen so many older amps like Soundstream and JBL that used crappy switches this was all it took.


HA! I'll give it a shot. Come to think of it, I was playing around with the crossover switch just before the sound went dead on the one channel. Could be an easy solution. The switches felt very good, but who's to say there isn't a little corrosion going on inside... I'll try doing that this weekend!


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## Dawgless (Oct 6, 2014)

Nearly finished with the amp. I've got all the caps replaced, as well as the power and ground wires. I need to solder in a longer remote lead and otherwise, I think I'm done. I'm going to keep the factory speaker wire and just solder these to the wires I'll be running inside the car to my speakers. 

I nearly ruined the amp last night though, soldering on some of the capacitors. there are eight caps that are part of the switching crossover section and there are super tiny, fragile leads that run from each side of the caps to the surface amount resistors and what look like PWM's. On one of the caps, the traces didn't connect, which left me with having to direct solder the cap, with it's correct polarity, to the correct pole on the PWM(think this is what it is), as well as the surface mount resistor. I'm going to get the board bolted back in place tonight and give it a test to see how it works. Right now, I give it a 25% shot at all four channels working as they should...


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## TrickyRicky (Apr 5, 2009)

Ha...you think those caps are little wait till you work on SMD/SMT. You need a magnifier most of time while working with SMD.


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## Dawgless (Oct 6, 2014)

TrickyRicky said:


> Ha...you think those caps are little wait till you work on SMD/SMT. You need a magnifier most of time while working with SMD.


Oh man, yeah, I can only imagine. I don't have a fine enough tip for my iron for any smaller than what I was working on last night... I wish there was a way to repair the traces that I doinked up. 

My biggest failure with the project was rushing the removal of the caps. I didn't heat up the joint, where the lead of the cap goes through the board, sufficiently enough to pull the lead out evenly. There were metal barrels that were in each of the through-holes that would pull out of the board very easily. This would break the super fine traces. All of the traces tested good, except for the one cap that I had to "franken-solder" back in. It doesn't look pretty, but it worked and I think it'll hold up. I'm not going to release public photo's of the repair, primarily because I'm embarrassed about it... Granted, I'm a rookie with amp repair, so I think I'm afforded a few mistakes, but I'm still not happy about it. 

Testing to commence tonight. Fingers crossed that it works.


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## TrickyRicky (Apr 5, 2009)

Check to see where the damage via holes traces go to and add jumpers wires on the bottom. Use something like 26g stranded wire as its flexible and easy to work with when repairing small traces.

If those traces are above the board then you might have to drill small 1/8" holes near the caps so the jumper wire goes from the bottom of the board to the top section were all the traces are. From there you can solder the other end of the jumper to the surface mount devices they go to.


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## Dawgless (Oct 6, 2014)

Oh man! That's great info!! I never thought of that. Guess that's why I'm on here posting my tales of woe... Thank you! 

Yeah, I ended up pulling the one cap, one of the 50v 10uf caps out of the board since there was no way to firmly secure it to the board, cut down the leads a bit, bent them to match, and then soldered the leads directly to where the traces terminated, one of which was a surface mount resistor, the other was one of the poles of a 8 pin PWM. 

In this pic, the third from the left cap is now soldered directly to one of the resistors between where the caps are positioned, and also to the back right pole on one of those 8 pinned PWM's.
http://s526.photobucket.com/user/FlytoFish/media/Unnamed%20US%20Amps%204-channel/SAM_2105_zpsdaec87fb.jpg.html[img/]

Since I had pulled the metal through hole pieces out of the board, there was no way to secure the cap to the actual board... Confusing, I know. Incorrect way of repair, most definitely. I'll probably need to add some hot glue or something to ensure the cap doesn't vibrate and break the connection with the terminals I soldered the cap to. 

TrickyRicky, I'll snap a picture tonight when I get home and PM it to you. I'm guessing you've seen some pretty shoddy repairs, so you can add it to your "epic fail" folder and get a good chuckle from it. :)


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## Victor_inox (Apr 27, 2012)

With Ricky and Randy you are in good hands here.


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