Re: Apple Multiple Scan 15AV Display.Help identifying a resistor
Good news!
I've replaced the resistors and the transistor. Swapped the neckboard. The monitor powered up... and stayed up!
The picture is all messed up but I believe this is normal when you swap a neckboard between tubes - all the adjustments are in there. Colours are off, brightness is too high and I can't turn up contrast without causing major smearing on the picture.
Only two potential issues
- Those blotches are still there. I am not sure the de-gaussing circuit works? I remember hearing this loud "boing" (sorry!) when turning on a TV and you'd see the picture wobbling for a few seconds while the coil was discharged. I don't hear/see anything here
- The 70V line. I was monitoring it and my meter only reads 31V. I'm wondering whether the picture is dim because the CRT driver is getting half of the expected voltage? Unless the voltage rises when adjusting the drive on the neckboard? Do you think that second transistor could get some feedback from the neckboard and drive the rail harder if necessary?
Anyways, the service manual has the complete procedure to re-adjust it. I'll put a mirror in front of it and try tomorrow!
For now: Yay! I found the fault! My first CRT!
Thanks so much for your help so far.
Good news!
I've replaced the resistors and the transistor. Swapped the neckboard. The monitor powered up... and stayed up!
The picture is all messed up but I believe this is normal when you swap a neckboard between tubes - all the adjustments are in there. Colours are off, brightness is too high and I can't turn up contrast without causing major smearing on the picture.
Only two potential issues
- Those blotches are still there. I am not sure the de-gaussing circuit works? I remember hearing this loud "boing" (sorry!) when turning on a TV and you'd see the picture wobbling for a few seconds while the coil was discharged. I don't hear/see anything here
- The 70V line. I was monitoring it and my meter only reads 31V. I'm wondering whether the picture is dim because the CRT driver is getting half of the expected voltage? Unless the voltage rises when adjusting the drive on the neckboard? Do you think that second transistor could get some feedback from the neckboard and drive the rail harder if necessary?
Anyways, the service manual has the complete procedure to re-adjust it. I'll put a mirror in front of it and try tomorrow!
For now: Yay! I found the fault! My first CRT!
Thanks so much for your help so far.
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