15-10-2018, 08:07 PM
Hi.
Well looking at the previous pictures I can see the CRT has definitely got worse. Why you may ask and I have an idea. Do you remember that a few years back there was a thread elsewhere about reactivating a CRT without damage. I was sceptical at the time as I had tried it with mixed results. One CRT after a week or so was worse than it was beforehand, I was still on the fence though. So as I had little to loose I did the same to the CRM92 in the Ekco. Initially results were good but after a rest of a few months the CRT is now worse than before.
I have done some work today restuffing caps, replacing wildly out of tolerance resistors and replacing perished wiring. Even though the CRT is low I came to the conclusion the picture was a bit limited with flat whites. A look at the video on the scope with a grey scale showed the peak white and to be clipping badly, it was fine on the SP41 grid, I replaced the valve and double checked all components with no improvement, Then I pulled the vision interference limiter valve and immediately the clipping disappeared. I checked all the components and replaced the limiter valve with no improvement, actually I'm running low contrast anyway and the clipping is still prevalent, I also replaced the DC restorer just in case, so for now the limiter is out of circuit.
I'll nee to fit the 7BP7 Radar CRT for a temporary check to see if the focus is OK and to see if the picture is up to standard. I hope to pick up a good CRM92 soon.
Well looking at the previous pictures I can see the CRT has definitely got worse. Why you may ask and I have an idea. Do you remember that a few years back there was a thread elsewhere about reactivating a CRT without damage. I was sceptical at the time as I had tried it with mixed results. One CRT after a week or so was worse than it was beforehand, I was still on the fence though. So as I had little to loose I did the same to the CRM92 in the Ekco. Initially results were good but after a rest of a few months the CRT is now worse than before.
I have done some work today restuffing caps, replacing wildly out of tolerance resistors and replacing perished wiring. Even though the CRT is low I came to the conclusion the picture was a bit limited with flat whites. A look at the video on the scope with a grey scale showed the peak white and to be clipping badly, it was fine on the SP41 grid, I replaced the valve and double checked all components with no improvement, Then I pulled the vision interference limiter valve and immediately the clipping disappeared. I checked all the components and replaced the limiter valve with no improvement, actually I'm running low contrast anyway and the clipping is still prevalent, I also replaced the DC restorer just in case, so for now the limiter is out of circuit.
I'll nee to fit the 7BP7 Radar CRT for a temporary check to see if the focus is OK and to see if the picture is up to standard. I hope to pick up a good CRM92 soon.
