BK Precision CRT tester (470)

[ChrisW6ATV]

I have seen quite a few (weaker, typically) CRTs that would not show any meter movement even with the G2 control all the way up. I would still proceed with testing them. If the test indicated "good", then I considered them "not fully good, but usable overall".

In other discussions of testing CRTs, the ability to get that "one division increase" (or equivalents on non-B&K testers) was described as the CRT "having good cutoff".

[TinCanAlley]

Originally Posted by ChrisW6ATV

I have seen quite a few (weaker, typically) CRTs that would not show any meter movement even with the G2 control all the way up. I would still proceed with testing them. If the test indicated "good", then I considered them "not fully good, but usable overall".

In other discussions of testing CRTs, the ability to get that "one division increase" (or equivalents on non-B&K testers) was described as the CRT "having good cutoff".

I'm starting to think a capacitor or such in the tester is going bad. I have three green/monochrome CRTs and all cannot raise the 1 division, but they each test differently for emissions. The one in my TRS-80 4 is bright and clear, but does poorly in emissions, my IBM 5151 test near the top of the good range and my Canon monitor tests poorly. None of them can raise 1 division for G2. There is a 50uf 450V capacitor, and I think I will remove and test. I don't have an ESR, so I have to pull it.

[Notimetolooz]

Actually I don't think that is the problem. During the emission test the G2 supply is used. Both the G1 and G2 are used to test cutoff. But you adjust G1 beforehand. By the way when you adjust G1 beforehand the meter shows voltage, in cutoff and emission the meter is looking at current. You could confirm G1 voltage during that adjustment by putting a meter on the G1 pin. You would need to connect the external meter other lead to the circuit ground inside the tester however, none of the test socket pins are connected to ground during that setting.

[TinCanAlley]

Originally Posted by Notimetolooz

Actually I don't think that is the problem. During the emission test the G2 supply is used. Both the G1 and G2 are used to test cutoff. But you adjust G1 beforehand. By the way when you adjust G1 beforehand the meter shows voltage, in cutoff and emission the meter is looking at current. You could confirm G1 voltage during that adjustment by putting a meter on the G1 pin. You would need to connect the external meter other lead to the circuit ground inside the tester however, none of the test socket pins are connected to ground during that setting.

I will give that a try tomorrow.

Thanks!