Here's what I'd do to make a definite diagnosis: Look at the vertical deflection plate voltages. If they look fine, then that pretty much leaves the crt as the only culprit. In that case, there's still a (slim) chance that the problem is external to the crt (e.g., a magnetized bit that is kinking the beam, although I don't recall any magnetizable bits being near the crt).
-- Cheers,
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
toggle quoted message
Show quoted text
On 2/10/2022 22:31, Morris Odell wrote:
Hi all,
I recently picked up a couple of 7904s with a stack of plugins. While most of the plugins are OK, the mainframes have some problems. One of them looks very good but is completely dead despite having intact fuses. It doesn't even tick. The other looks like it's had a hard life but at least powers up. The vertical and horizontal systems work OK but the calibrator and the readout do not. Also the displays look Ok when the beam is at the lower part of the screen but develop a kink when it is shifted upwards. The geometry and astigmatism controls do not correct it. This happens regardless of the vertical or horizontal settings and al all timebase speeds. Is this a sign of a damaged CRT?
I'd like to end up with two working 7904s but If the CRT is the problem than I might as well try to make one good one by swapping modules.
Any advice gratefully received!
Morris
