|Okay you are new at this .. I don't know about your model tester, but some have a light bulb as a fuse right on top of the panel .. If you do need to take out all 20 of the screws, go ahead and do that .. If you have any kind of ohm meter ( or get one ) just check the line cord, the on off switch, and the primary & secondary of the transformer .. It does have a rectifier tube, if you have AC from the transformer, you can check for open filament on that tube too .. Maybe just something simple .. If not, post again .. Someone can talk you through more ..