Hi to all, again with a questions and sorry for my english.
I have buyed a Mac Classic computer (probably 2mb because it have a little ram board connected on the logic board but without sim inserted and jumper setted on SIM NOT INSTALLED). The system not boot up and the screen turn on with a garbage static image and square have a fast flickering, nothing bong!
I have disassembled all because logic board have capacitor leaking (little but present) and very poor state, battery is without leak but 0 volt, i have removed this and at this moment the system don't have a battery.
Then i washed the logic board and recapped it with new capacitor.
Then i have reassembled all and turned on, the screen appear with full horizontal lines but after 2 minutes the system bong and boot up from SCSI hdd (OS7.1) . After 10 minutes of working the system going to continuosly resetting, infinite, and in any case it try to boot then reset again or screen stays with garbage image or freezed.
I have measured 5v rail and 12v rail, and with multimeter i have an oscillation from 4.5v to 5.1v on 5 volt rail and 11.5v to 12,7v on 12 volt rail. At this point i have decided to check the analog board in switching power supply section.
At first look all of output electrolytic capacitor have a leaking and it have corroded part of bottom wiring side, i have replaced only all output capacitors and cleaned board and all damaged solder point, and cleaned all connectors.
Try to turn on, system boot up normally, load OS from disk, and...... again after any minutes the system going to reset continuosly!
On the service manual i have readed section of votlage regulator trimmer resistor, i have turned on system and regulated it to have stable 5,1volt and 12,5 volt on output, the computer seems to work...........but..........after one day i have returned on it and again horizontal lines and same issue!
Now if i measure 5v lines and 12v lines after 2-3 hour of stop i have noted a time increasing voltage, when the system is cold, and stabilize it when hot, the system try to boot up when i have 4,9volt on multimeter, if it is down of this value the system is hanged, or resetting continue. Also i have noted the SCSI disk not spin every time computer turned on, seems spin when the voltage is ok and, i have noted also the voltage drop down when system going to continuosly reset, both 5 volt drop rapidly from 5 to 2 volt and 12 volt drop rapidly from 12 to 9 volt.
Finally, in any case the systen boots up and working for about 10 minutes, or other case i have the issue at first boot time.
I think so the voltage regulation and checnking circuit have a problem, or other capacitor need to be replace on analog board.
Can any one help me?
Thanks
Emanuel
I have buyed a Mac Classic computer (probably 2mb because it have a little ram board connected on the logic board but without sim inserted and jumper setted on SIM NOT INSTALLED). The system not boot up and the screen turn on with a garbage static image and square have a fast flickering, nothing bong!
I have disassembled all because logic board have capacitor leaking (little but present) and very poor state, battery is without leak but 0 volt, i have removed this and at this moment the system don't have a battery.
Then i washed the logic board and recapped it with new capacitor.
Then i have reassembled all and turned on, the screen appear with full horizontal lines but after 2 minutes the system bong and boot up from SCSI hdd (OS7.1) . After 10 minutes of working the system going to continuosly resetting, infinite, and in any case it try to boot then reset again or screen stays with garbage image or freezed.
I have measured 5v rail and 12v rail, and with multimeter i have an oscillation from 4.5v to 5.1v on 5 volt rail and 11.5v to 12,7v on 12 volt rail. At this point i have decided to check the analog board in switching power supply section.
At first look all of output electrolytic capacitor have a leaking and it have corroded part of bottom wiring side, i have replaced only all output capacitors and cleaned board and all damaged solder point, and cleaned all connectors.
Try to turn on, system boot up normally, load OS from disk, and...... again after any minutes the system going to reset continuosly!
On the service manual i have readed section of votlage regulator trimmer resistor, i have turned on system and regulated it to have stable 5,1volt and 12,5 volt on output, the computer seems to work...........but..........after one day i have returned on it and again horizontal lines and same issue!
Now if i measure 5v lines and 12v lines after 2-3 hour of stop i have noted a time increasing voltage, when the system is cold, and stabilize it when hot, the system try to boot up when i have 4,9volt on multimeter, if it is down of this value the system is hanged, or resetting continue. Also i have noted the SCSI disk not spin every time computer turned on, seems spin when the voltage is ok and, i have noted also the voltage drop down when system going to continuosly reset, both 5 volt drop rapidly from 5 to 2 volt and 12 volt drop rapidly from 12 to 9 volt.
Finally, in any case the systen boots up and working for about 10 minutes, or other case i have the issue at first boot time.
I think so the voltage regulation and checnking circuit have a problem, or other capacitor need to be replace on analog board.
Can any one help me?
Thanks
Emanuel