Hello all
recently picked a joblot of early 68k macs. 128/512/plus! To save time, I have resurrected the analog board from the Mac 512 along with its motherboard for a play.
issues appear to be when the computer starts up, a pop from the speaker is audible, and then junk on the screen. I will attach a video link demonstrating the issues. Sometimes I then get more periodic pops from the speaker.
so far I have gone over the analog board and checked everything I possibly can. Solder joints ok, I have measured and analysed the D.C. outputs. Nice clean DC, pretty much on the money on all rails.
I have cleaned connectors, reseated Rom chips and so on - no change.
the dead Mac scrolls do not mention such a fault.
I’m personally not suspecting caps as I’ve checked those on the logic board and appear to not give off terrible ESR and read within 10 percent of the values. I’ve probed
all voltage rails on the scope and confirmed no ripple.
I’ve heard people say these early ones have bad ram - how would one check that then?
thanks
Ed
recently picked a joblot of early 68k macs. 128/512/plus! To save time, I have resurrected the analog board from the Mac 512 along with its motherboard for a play.
issues appear to be when the computer starts up, a pop from the speaker is audible, and then junk on the screen. I will attach a video link demonstrating the issues. Sometimes I then get more periodic pops from the speaker.
so far I have gone over the analog board and checked everything I possibly can. Solder joints ok, I have measured and analysed the D.C. outputs. Nice clean DC, pretty much on the money on all rails.
I have cleaned connectors, reseated Rom chips and so on - no change.
the dead Mac scrolls do not mention such a fault.
I’m personally not suspecting caps as I’ve checked those on the logic board and appear to not give off terrible ESR and read within 10 percent of the values. I’ve probed
all voltage rails on the scope and confirmed no ripple.
I’ve heard people say these early ones have bad ram - how would one check that then?
thanks
Ed