Repair of Kewtech K71 PAT

[Big JJ]

Hi

I have been working on a KT71 Pat tester, which powers up past self test but will not do anything when buttons pressed.
 I have fixed quite a few of these over the years but this one is harder. Previous were power supply related etc.
Does anyone have a schematic for one of these. Kewtech tell me they will not provide and they no longer repair them.
So, more land fill if I cannot fix it.