A few weeks ago I purchased a pair of used Hypex NC400 based monoblock amplifiers from user on an audio website I frequent.
Taking the top cover off I wasn't happy with the quality and decided to rebuild them. Here is the teardown before the rebuild.
The underside had a piece of felt on it, but that surface needs to be able to radiate any heat from the amplifier module. The felt would act as a thermal insulator.
Removing the felt, the screw holes to hold the NC400 module in place were mangled, and filled with a white compound. I'm glad to say that a 99% iso-propyl alcohol solution removed the adhesive.
Removing the top cover, the internal wiring was unsecured, and used 20 gauge solid core wire for internal mains wiring. The soldering of wires to terminals was 'minimal', and all of the live terminals were bare. The colors of the wires in non-standard. The ground to the chassis uses the wrong type of connectors. There is no locking washer. The earth wire is thinner than the neutral wire.
Internal wiring was loose and unprotected. The power switch (which has no external indication of status) used screw down connections, but one of the wires pulled free easily. Live wire between the switch and SMPS is rubbing on heatsink.
Broken screw boss on front bottom right of case.
The mangled screw holes shown above meant that the NC400 module (the round PCB above) was only secured with heatsink compound (well I think it is heatsink compound, can't be sure). I've not managed to remove it yet. The anodizing is rubbed off around the holes for the standoff, which is a good thing, but the burr on the screw hole means there is a poor contact, and that is the main ground for the lower panel.
But wait, there's more ...
Perhaps the most surprising issue is that the binding posts for the speaker connections are in contact with the rear panel. I'm amazed the amplifier modules work at all as that must be a short circuit.
The black and red grommets in the picture below are shoulder washers. The holes in the back panel should be sized so that the smaller diameter of the washer fits into it, insulating the binding post from the chassis. The little pin shown on the red one should fit into a notch in the panel to stop the whole post from turning.
When I removed the nuts and insulators it gets even worse. As far as I can tell there is no insulation between the posts and the back panels! I'm amazed the amplifier modules didn't blow.
So now everything is stripped down. I still need to figure out how to remove the heatsink on the amplifier module without breaking anything.