Had a Hummy HDR some time ago that I "acuired" as non-working. Turned out to be acracked track under the PSU board (If I recall correctly, around the inductors close to the output conections). A few minttes with some tinned stranded wire and careful bridging all the dodgy track and it was running again.
You could check the PSU capacutirs - some fail.
See also some dedicated Hummy forums
Loads more out there.