MA Audio HK4000D Repair

MA Audio HK4000D Amplifier

This amp came from the Internet, it did not work according to the customer, he had taken it apart to check it out and put it back together, didn't see anything wrong, but for whatever reason it would not work. It was in very dirty condition, and had a lot of missing screws and some cosmetic damage.

Click image to Enlarge the image

First thing I noticed was the RCAs are all bent up, well the front plate
of the amp was anyway. Called the customer because I thought it happened
in shipping, but he said it was already like that. Also when I picked it up I noticed it sounded like screws were rolling around loose inside the amp.

A front shot, you can see the damage to the plate.

I took the cover off and noticed it was really dirty, the fan was broken
loose from the board, there are missing screws and lots of crooked clamps
that were loose.

Here you can see one of the clamps is missing a screw and is obviously not
installed correctly. If this amp were to be operated like this for very
long (more than 30 seconds at half volume or more) the output section
would go up in smoke, and be an expensive repair bill.

Some more loose crooked clamps and you can see the circuit board is
very dirty.

Look under the display you can see some more crooked clamps and
also notice the fan looks like it was broken from it's holding screws...
Maybe it's not the original fan, someone took it out of something else
(like a computer power supply maybe) and stuck it in this amp because
the original fan went out or something. I don't know. Either way it needs
to be secured to the main board.

All cleaned up straightened out and screws replaced. I didn't get any
more pics of the process, had to charge the batteries in my camera and I
could not twiddle my thumbs for an hour, so I worked on the amp while the
batteries charge. The board was removed completely from the sink, all old
heatsink compound was removed, Air Compressor used to clean the board and
the heatsink, solder connections touched up on the input board. Fan was
secured to the mainboard with adhesive and I even straightened out the bent
front plate where the RCAs go. Then I put it all back together nice and straight and clean.

Maybe not 100% perfect, but definately much better than it was...

Here you can see where I used a flexible adhesive to secure the fan rather
than finding new screws. Screws might eventually vibrate loose or could
crack the plastic housing of the fan, so I used the adhesive on all 4
corners, it should hold just fine.

Notice the reflection of the clamp bars on the sides of the heatsink. The
flash is off on my camera, it's just that clean and shiny now... little
TLC makes a big difference.

The front area of the mainboard and input board near the RCAs. Notice I
had to use a nut as a spacer on the new screw, they were a little longer
than the original screws. Also this is the area that needed touching up on
the soldering. This board also houses the last output FET on each side of
the amp, so these solder connections are very important. If disconnected
the output section could fail.

In the middle of this closeup pic, there is a blue and white capacitor and
a screw next to it. This is a support for the center of the main board to
keep it from getting damaged by flexing. These screws MUST remain tight,
so I tightened them real snug and the purple junk on that nut is a dab of
Krazy Glue to make sure it doesn't rattle loose.

Input end of the assembled amp.

Power and output end of the amp.

Overhead shot, amp turned on, working fine.

This amp has a neat little LCD display, shows voltage, Temperature and
relative output. When sound is being reproduced by the amp, the little
speakers have a bar meter that moves with the music.

This is what it looks like with no music playing.

This is a pretty good size amp. I am not sure about the claim of 4000
watts, it has a healthy power supply, but the output section doesn't seem
to be beefy enough to produce 4000 watts without a lot of distortion.
But still, it should produce 2000 watts @ 2 ohms with little effort. A
good sub amp.

This amp just needed some TLC, not sure if these pics do it justice, but it did turn out pretty nice after I cleaned it up and straightened it out. Although I didn't do any major work on this amp, it was very time consuming to get it to this good of shape from what it was, so the bill was for 2 hours @ $40 per hour standard Class D amp rate. So it was $80. I think well worth it, to me this amp sounded great and it is powerful.