b&k tube tester model 606 problem

[kramden66]

Here is the problem all of a sudden it wont read shorts/gas. The resistors seem to be ok and the what 2 capacitors and it wont indicate anything. The lamp is ok and even if you select the two same numbers like 7 and 7 the lamp should light and it doesn't. Any ideas on what's wrong? The tube inside is the only this I can think of but checked it on a different tester and it reads good emmisions but that's all I can say about the tube. Is there something I overlook. Thank