The facets of InP/(Al)GaInP/GaAs quantum dot laser active regions offer superior resistance to catastrophic optical mirror damage at high facet power densities. These structures degrade by bulk damage. We have used a new range of techniques to identify changes occurring during damage in working devices: thermography through windows in the nmetallization, photoluminescence via p-metallization windows and photocurrent studies. Devices were aged with single very high current pulses or pulses of increasing size and monitored during this process with these techniques. Previous investigation with panchromatic cathodoluminescence revealed dark non-radiative spots throughout the plane of the active region. The dark spots, which were present even in unprocessed material, increased in size in the pumped regions only during lasing action. The spots and background regions darkened throughout the pumped stripe area only for the whole duration of the current pulse. Thermography after successive pulses confirmed damage originating from a point in the bulk rather than at the facet. p-windows observations of light and dark regions showed a blue shift in the photoluminescence spectra of the dark regions. Photocurrent studies of more gently aged devices showed a greater decrease in signal in the region associated in previous work with defective very large dots. Identification of such spectral regions, which were previously found to be influenced by changes in structure design and growth conditions offer a route to control degradation mechanisms by this means.