Hi there! 
I start this post to share my ongoing analysis to get an hardware solution x a not working mac 128/512k analog board.
The problem that is evident with a white line up in the screen, comes as i did an error... unfortunately when i assembly back all, i forget the grounding cable that exit from the connector in J2 disconnected in its top left monitor screw, free positioned near the bottom Fuse on the analog board. Monitor is fine, mainboard is fine, with DMM i found faulty Q1, U1 and the 2N5425 (Q5) that i substitute. Before this change there where only a bottom up bright line without any background.
As i already mention ubove, the problem is visible by a bright horizontal line and some of the screen in the back compressed to the top if the screen.
https://www.dropbox.com/s/rcmtmlh2b2r2rhh/IMG_5979.jpg?dl=0
I red L. Pina suggestions as other posts on forums and i asked also some more thougts to TechKnight ( allways really clear, thanks! . ), but after more check following all these feedback i get to the conclusion that the problem may need more work and help to found its solution. So that i start this topic.
The evidence of this horizontal brght line seems to be normally dude to one or both of the main output transistors died. ( but both to me now are fine)
I controlled Q1, Q2, CR2, CR3, CR4, and U1. All fine; with DMM set to diode i see that x U1 checking between pin 1 and 7 it do not go to continuity... that is what happen in another working Board i see to easy compare values.
Maybe someone has some experience nd other auggestion to an help for the solution.
thanks!
I start this post to share my ongoing analysis to get an hardware solution x a not working mac 128/512k analog board.
The problem that is evident with a white line up in the screen, comes as i did an error... unfortunately when i assembly back all, i forget the grounding cable that exit from the connector in J2 disconnected in its top left monitor screw, free positioned near the bottom Fuse on the analog board. Monitor is fine, mainboard is fine, with DMM i found faulty Q1, U1 and the 2N5425 (Q5) that i substitute. Before this change there where only a bottom up bright line without any background.
As i already mention ubove, the problem is visible by a bright horizontal line and some of the screen in the back compressed to the top if the screen.
https://www.dropbox.com/s/rcmtmlh2b2r2rhh/IMG_5979.jpg?dl=0
I red L. Pina suggestions as other posts on forums and i asked also some more thougts to TechKnight ( allways really clear, thanks!
. ), but after more check following all these feedback i get to the conclusion that the problem may need more work and help to found its solution. So that i start this topic.The evidence of this horizontal brght line seems to be normally dude to one or both of the main output transistors died. ( but both to me now are fine)
I controlled Q1, Q2, CR2, CR3, CR4, and U1. All fine; with DMM set to diode i see that x U1 checking between pin 1 and 7 it do not go to continuity... that is what happen in another working Board i see to easy compare values.
Maybe someone has some experience nd other auggestion to an help for the solution.
thanks!
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