# PPI a404.2 Project Repair Refurbish



## nikb47 (Oct 21, 2013)

I just started on a repair/refurbish on one of my amps. 96 PPI Art series a404.2 It had lots of noise coming from right rear channel. I bought this thing to repair it, it had been opened by the previous owner. Upon inspection 2 resistors are MIA at R185 and R186 right by the rca in's (the 10ohm 5% 2 watt) and you can see on the board where they got hot. I went ahead and pulled R137 and R138 which looked a little tan like they got a little hot, although they did test out good.





I did a quick continuity check on the transistors and they all seem fine, although there is one that seems to be different than all the other ones. It is located at Q5.



Almost all of the caps looked like they were starting to leak. But those were on the list already! Upon removal of capacitors I found the cap at C10 had one leg broken off! It was the positive leg.



I have all caps and resistors on the way from mouser.com and I've already begun pulling caps. I am going to fix these things mentioned and then see if it will come back to life with clean power. Stay posted for updates within the next few days. Also, if anyone has any other suggestions as to what may be the cause of noise at right rear let me know. Oh, and if the experts want to chime in feel free! Thanks for stopping in!


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## Darth SQ (Sep 17, 2010)

nikb47 said:


> I just started on a repair/refurbish on one of my amps. 96 PPI Art series a404.2 It had lots of noise coming from right rear channel. I bought this thing to repair it, it had been opened by the previous owner. Upon inspection 2 resistors are MIA at R185 and R186 right by the rca in's (the 10ohm 5% 2 watt) and you can see on the board where they got hot. I went ahead and pulled R137 and R138 which looked a little tan like they got a little hot, although they did test out good.
> 
> 
> 
> ...


I was going to say based on the noise I'd bet on cap issues but you're already all over it. 
Looking forward to a good outcome on this. :thumbsup:

BTW, what's all the black speckled crap on the ground bar?


Bret
PPI-ART COLLECTOR


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## nikb47 (Oct 21, 2013)

1 more thing. I got it off of ebay. If you read through the description the seller states " Board shows no signs of burns/repairs (SEE PHOTOS)!!!!!" But you can clearly see that the resistors got hot at R185 and R186, and they're not there! lol whatever... I guess I should have looked closer at the pics... Here's the auction: http://www.ebay.com/itm/PRECISION-P...dMJT7L%2BemxM2xqEaplg%3D&orig_cvip=true&rt=nc


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## nikb47 (Oct 21, 2013)

Bret,

I had to go take a look at the ground bar it's not black spots, just looks funny kind of like hard water or something on it.

ETA: Almost looks like galvanized metal or something.


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## vwdave (Jun 12, 2013)

if the noise is caused by a faulty cap I would think it wouldnt be one from the power supply. I would look at the transistors (like you did) and test out as many resistors as you have patience for. that coil looks like its been burned as well, I have the same thing on a 2300 that I fixed up. it shouldnt effect how it sounds though.

go as big as you can on the power supply caps (higher capacitance) while still keeping the same size capacitor. you should be able to get more farads now with newer, better technology. also, get it rated for at least the original temp, maybe higher if you can.

what FETs are on there? maybe there are upgraded ones available.

you got to experience the joy of buying broken amps on ebay. its hit or miss when you do it, but you should always expect it to be a challenge.


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## nikb47 (Oct 21, 2013)

Vwdave,

Thanks for your reply. For right now im just going to fix the aparent problems. (Leaky caps and missing resistors) after that if I still have a problem I will investigate further. Im not in any way ruling out your advice though. As for the coil, I dont see anything that looks burnt, maybe you can point out what you're seeing. 
For the caps I went with the same as original but higher temp rating and supposed to be lower esr. Also which ones are the power supply caps and which are for output?


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## Darth SQ (Sep 17, 2010)

nikb47 said:


> Bret,
> 
> I had to go take a look at the ground bar it's not black spots, just looks funny kind of like hard water or something on it.
> 
> ETA: Almost looks like galvanized metal or something.





Ok...here's my A404.2 after fully being recapped and reconditioned.
I'll put money that the black spots are from leaking caps that were right next to it.
Good thing the board still looks really good.





















Bret
PPI-ART COLLECTOR


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## nikb47 (Oct 21, 2013)

Bret,

Yeah that would make sense about the leaky caps. I've got all of the caps removed from the board now I'm just going to clean it up while I wait for the parts. Oh and I ordered the wrong resistors. Had a major brain fart and ordered 20 ohm 3 watt??? Don't know how I did that... I guess I'll place another mouser order....


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## nikb47 (Oct 21, 2013)

Ok, so since the one power supply fet seems to be different, I have decided I'm going to go ahead and replace all the transistors and rectifiers on this thing. So the power supply mosfets are the irfz43n. Should I replace them with original or is there a good replacement? The rectifiers are byw29f-200. Again any replacements? And then the 2n6490 and 2n6487. Thinking of going with the 6491 and 6488. Thanks!


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## nikb47 (Oct 21, 2013)

1 more thing. Is there any op amp upgrades that would be worth while?


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## nikb47 (Oct 21, 2013)

Never mind on the upgrades. Most of my parts are coming in tomorrow. Updates will be soon!


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## nikb47 (Oct 21, 2013)

Got a little done today. Put a handfull of caps in. Kapton is installed. I will finish up first thing in the morning. I just need to get some silicone thermal paste and I should have everything! I also built my clamp bar for testing.










Eta: also cleaned more of the old paste off after the picture.


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## Darth SQ (Sep 17, 2010)

nikb47 said:


> Got a little done today. Put a handfull of caps in. Kapton is installed. I will finish up first thing in the morning. I just need to get some silicone thermal paste and I should have everything! I also built my clamp bar for testing.


Nice progress. :thumbsup:


Bret
PPI-ART COLLECTOR


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## nikb47 (Oct 21, 2013)

Ok got it put back together and powered it up. Buzzing noise coming from the output side. Cant tell exatly where but it sounds like from the output transistors. What next? Lol

Edit: also still has static from right rear and low impedance light is on still which i didnt notice before but it does say that on the ebay auction.


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## nikb47 (Oct 21, 2013)

Ok with multi meter in diode with red on leg 3 im getting some funny stuff on 6 of the transistors. Q7 Q8 Q68 q69 q72 q73 2n6490's

Red on leg 3 stationary
Leg 1 .043
Leg 2 .700 and climbs to 1.062 probably more if i hold it there

The 2 remainder 6490s at q10 q11
Leg1 .043
Leg2 .132


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## nikb47 (Oct 21, 2013)

Ok i just checked my a600.2 and it does the same thing so im guessing thats normal


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## nikb47 (Oct 21, 2013)

Hello all,

Just wanted to make an update.

I ended up replacing all of the output transistors. I had 1 shorted. The amp was no longer in protect mode and was no longer buzzing. BUT I still had problems. the right rear channel dc offset was at ~1v dc still and the ac bias on that channel would not change the ac amperage draw.

I went ahead and pulled the sip card and found 1 shorted transistor on it. I popped a know good sip card in and was still having some issues. still high dc offset and still static.

After talking to 1moreamp and Perry Babin over on diyaudio, 1moreamp advised me to check out the driver transistors. I found 2 of them shorted. I should have listened to him because he told me to check those long ago and they are only about 3c a piece so go ahead and put new ones in. 

Now the amp is working like a champ. I have adjusted the bias and dc offset and it has been purring like a kitten for a few days now!


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## Darth SQ (Sep 17, 2010)

That's a good ending to the story.
You're the official new resident DIYMA Art repair tech now. :thumbsup:


Bret
PPI-ART COLLECTOR


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## nikb47 (Oct 21, 2013)

Thank you for the kind words Bret! 

I gotta say that it wouldn't have been possible without the help of Perry Babin and 1moreamp over at WWW.diyaudio.com . I would also highly recommend Perry's amplifier repair tutorial! Even the one that he offers for free has TONS of very good information for anyone looking to repair amplifiers. I figured that since he offers his knowledge on the forums the least I could do was buy the full version and it is very handy. 

1moreamp knows these amplifiers like the back of his hand and everything that he said was wrong with the amp he nailed on the head! I have definitely learned a lot and will continue learning because I actually really enjoyed doing this. 

I have bought some other amps from local pawns and such for dirt cheap and got quite a few of them going so I can see this as a nice money making hobby for myself. Anyway... that's enough rambling for me. Have a good day everyone.


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