NAD D3020 v2 Amplifier Protection Mode

[raso]

I picked up on eBay a spares/repair NAD D3020 v2 amplifier for $70. It will turn on and then flashes red and turn off. I couldn't find the service manual for V2 but another post here did have it for V1 (https://www.eevblog.com/forum/repair/help-repair-a-d-class-amplifier-nad-d3020-v1/). They seem to be very similar with the main difference with the V2 having a Phono Input - which is why I want it. Service manual says red light means "Check Protection Circuit".

The Amplifier is an OEM UcD102 (https://www.hypex.nl/product/ucd102-oem/52) unit from Hypex which the spec sheet says has DC-Error Detection on the output. I found a test point on the main board (DCERR) and it does go high on startup. Disconnecting the amplifier completely does allow the unit to power up and even the headphones work (separate amplifier) - so not a complete loss if I just use it as an Headphone amp with Phono.

After some probing around it looks like 2 of the Main MOSFETs on the UcD102 are blown (short between source and drain). Sure enough when I check the output terminal for that channel there is -28DC volts on it. Good thing I didn't hook up any speakers to it.

While I wait for the replacement MOSFETs to arrive should I keep looking for other problems? Not sure why they would have blown, could be heat I guess since the unit is very compact with no active cooling (just a thermal cutout on the amp heatsink)

P.S. For future generations trying to dissemble this amplifier.

Remove the two screws on the back, then peel off the label plate - its glued on!!. You can then remove the four outer screws, 2 for each side panel. Then you can pull off the side panel with the NAD logo - careful there are plastic clips (bottom seam, top inner, front inner) . You should be able to slide out the amp now and flip it over. The other side panel is attached to the top/front with screws you don't need to remove it since you can disconnect the wires going to the display/controls/antenna.

To get to the amp board remove the 3 screws on the main board and the screw between the optical and coax digital input on the back. The main board is connected to the lower board with a very tall standoff. Gently pull the board back (to clear the digital coax jack) and up being careful with the standoff.

As they say "You are in like Flynn"