One thing you can do is use a ccd camera (webcam mobile phone) to look for ir. Place a white card a few inches from the output and look at the card through the camera. If you see a pink/purple glow then there is ir being emitted. If its really bright then the head may well be working but the SHG may not be functional. If you see no glow on the card try pointing the camera directly into the laser output window. This may seem daft but if there is enough ir coming out to damge the camera you would see the glow on the card. Doing this you may see some ir glow inside, if you do and its faint then the diode may well have gone to diode heaven.