Mach460 Amp Bad. Anyone take one apart?

[Sagittaria]

In the attempt of saving myself 60 bucks I decided to do some research into my blown 460 amp. It is indeed the amp because I can swap the good amp into both spots and the corresponding speakers will work.

Pulled it apart but I don't see any blown or charred resistors that most people normally find when their amp is blown - in fact all the components look fine. Anyone have any ideas or experience?

 

[brendan.9]

buy a new better one? or i have 2 sitting in my garage i'll never use.

 

[nextime]

One of the solder connections could have failed. Most electronics now float through a pool of solder and when they get old one solder point can crack. I had this on a TV..... took hours to diagnose and re-solder 1 connection.

 

[Sagittaria]

I'm not prepared to gut the mach 460 just yet. With some new tweeters and a head unit it actually sounded pretty decent.

Thanks brenden, all the solder looks good. I kinda wish it was failed connection though

I've determined it is a bad MOSFET following up on some older threads saying they were a common fail point. I've ordered some upgraded replacements.

While I'm at it I ordered upgraded caps for the ten year old general purpose Nichicon VXs for some Panasonic FMs (for the 4 power caps) and Nichicon KAs (9 audio path) for cheap. Total of 13 to recap - pretty easy. I will keep you posted to see how much this improves sound quality.

 

[nextime]

The 460 is just an AMP, nothing more really.

 

[Sagittaria]

The 460 is just an AMP, nothing more really.

A little more than that unfortunately. All four "sub/super sound" speakers are wired in parallel in pairs... doors/backs. All of them are 6 ohms so the amps see 3 ohms... so no standard 4 ohm speakers (amps see 2 ohms) can just be swapped in without blowing amps up - which is why I said earlier that most people end up wiring up a whole new system and that I'm not ready to drop the dough on that... nor do I espicially like the idea of losing the ergonomics/stock look of the interior... (random amp bolted up somewhere). Especially if I can make the stock system sound pretty decent for cheap.

Anyways here it is with new MOSFETs, all new quality caps, and a few higher tolerance resistors redone.

Amps are working again and the lows sound a lot cleaner. I was pretty surprised at how much clearer. Still have a minor issue with a little lackluster mids (since I ripped out the tweeter/mid speakers for regular tweeters)... I've compensated with my head unit as much as I could.

Anyways, it sounds pretty darn good I think and the mach 460 has some pretty good bass in a stock system especially w/ no sub. I'm happy.

 

[shurur]

So just as a finish to this most excellent thread..

which schematic/amp pc brd designators are the parts you replaced and what did you replace them with??

I think i can see the ones you replaced in the picture, but I'd like the specific info.

Thanks again...

 

[Sagittaria]

(For one amp)
2xPanasonic FM 50v 1000uf EEU-FM1H102
2xPansonic FM 16v 2200uf EEU-FM1C222
1xNichicon KA 16v 33uf UKA1C330MDD1TD
7xNichicon KA 35v 10uf ECE-A1VKA100
1xNichicon KA 50v 4.7uf EEU-FM1C222

Total of 13 electrolytic caps total on the boards. Recapping amps is a common audiophile way of improving sound... especially in older boards (caps worsen as they age... they filter signals and are the single greatest reason for bad sound). The OEM nichicon VXs are actually decent but they are more of a middle of the road general purpose sort of capacitor. The FMs are considered to be among the best (currently) but some of the smaller caps proved to be difficult to get the right specs for... which is why I chose the KAs. They are Nichicon's "premium audio caps." See following chart if you're curious: Miniature Type Aluminum Electrolytic Capacitors

I bought all my stuff through digikey. Here are the replacement MOSFETs... however I wouldn't bother replacing these unless you actually have a problem. They handle a little more current yes... but your stock ones aren't necessarily going to blow.

2x 100v 33A IRF540NPbF (MOSFETs... they supply power to the amp)
2x Any .5w 56ohm 5% or 1% resistor of your choice... stockers are rated at .25w and have a tendency to blow before the MOSFETs do... they regulate how much current goes to the MOSFETs. They are labeled r807 and r808 - right in front of each MOSFET.

The Mach 460 board isn't complicated by any means especially when compared to modern compact SMD boards - but I would recommend you have some pretty good soldering experience with on PCBs.

And for others curious on the whole recapping thing - here is a decent guide
http://www.condoraudio.com/wp-conte...oose-Replacement-Capacitors-and-Resistors.pdf
I really only took the easy route and just replaced capacitors.

 

[shurur]

Sagitaria,
I have to say this is another one of your golden threads.
I was a tech..then engineer (down-sized/ousourced/ostricized)...but stuck in digital design..my analog is not so good. thanks again.

 

[Sagittaria]

I appreciate the kind words sir! All is still well with my amps.