rich@island.uu.net (Rich Fanning) (01/11/90)
I have an original 128K Mac which will soon be reaching its fifth birthday.
Alas, in the last few weeks something odd has happened to the brightness
of the screen. Before, the brightness control adjusted it from completely
dark to fairly bright. It now goes from fairly bright to REALLY REALLY BRIGHT.
Is there a simple fix?
--
Rich Fanning | "Thinking is more interesting than
{uunet,sun,well}!island!rich | knowing, but not so interesting as
| looking" - Goethemyers@hpfcdj.HP.COM (Bob Myers) (01/16/90)
>I have an original 128K Mac which will soon be reaching its fifth birthday. > >Alas, in the last few weeks something odd has happened to the brightness >of the screen. Before, the brightness control adjusted it from completely >dark to fairly bright. It now goes from fairly bright to REALLY REALLY BRIGHT. > >Is there a simple fix? I don't know the particulars of how the display in the Mac is designed, but with most monitors I'd be suspicious that the screen voltage - usually supplied by a divider off the high voltage circuit - was out of adjustment (esp. if the retrace lines are now visible on the screen). Look for a control on or near the flyback transformer marked "SCREEN", and twiddle it. If this isn't the problem, the likely causes are - roughly in order - 1. Bad video amplifier board (or check for an internal "master brightness" or "contrast" control on or near the video amp). 2. Bad CRT. STANDARD WARNING: CRT displays use EXTREMELY HAZARDOUS voltages. If you are not absolutely certain that you know how to SAFELY adjust and repair such equipment, please refer such servicing to qualified personnel. Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other myers%hpfcla@hplabs.hp.com | sentient life-form on this planet.