68kMLA Classic Interface

This is a version of the 68kMLA forums for viewing on your favorite old mac. Visitors on modern platforms may prefer the main site.

Click here to select a new forum.
No High Voltage on CRT
Posted by: DomDom on 2023-04-21 20:24:55
After recapping my Macintosh classic I was still getting the checkerboard pattern and while I was probing for voltages the screen went out and there was no High voltage on the CRT. I did check the fuse, replace the mofset, and after checking the voltages the connector from the logic board to power supply everything was connecting and a perfect 5V and 12V with logic board plugged in. I know there is no high voltage generated when the power supply detects no logic board so does anyone know what could be holding it back from powering on? I haven't checked my cap job too well so I will check that tomorrow morning to see if anything is shorting. Thanks, anything helps!
Posted by: DomDom on 2023-04-22 07:31:05
After a bit of Fiddaling, i've found that the pads for the capacitor on c5 are shorted and when testing continuity on the 5v rail and ground they are shorts so what can I to find this short to ground
Posted by: Nixontheknight on 2023-04-22 13:51:37
After a bit of Fiddaling, i've found that the pads for the capacitor on c5 are shorted and when testing continuity on the 5v rail and ground they are shorts so what can I to find this short to ground
if you have a thermal camera, you can use that to figure out what component gets hot first when you switch it on, then replace the component that gets hot first
Posted by: chiptripper on 2023-04-23 19:01:35
Did you clean the logic board after the recap?

Have you recapped the analog board too? If not, that will need to be done.

Also check for cracked solder joints at the back of the AB, particularly at plug connectors. That a ill definitely cause video glitches like you describe.
1