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.
Macintosh II recapped, got chime but no other action
Posted by: Falter on 2019-05-21 22:02:00 Hey guys, So I have this Mac II that I've had for eons, and it sat for about 8 years and the caps went bad. I can see some light corrosion here and there, including the legs of UB1. Anyway, it would not power on. One of the PRAM batteries was dead, I replaced both with 3.6V (they were 3.0V, I've read mixed things in different forums as to what voltage is correct). Still would not start. So I replaced all the SMD caps. It still does not start off the keyboard or back switch, but it does jump start and play the usual Mac chime. However there is no video and it does not try to boot anything. Would appreciate any suggestions on what to look at next. I did the battery replacement a long time ago, and then shelved the unit. For some reason I recall one of the batteries having its polarity reversed from the first one. No idea why that would be, given the positive is clearly marked on the same side of each battery on the silkscreen.
Posted by: LaPorta on 2019-05-22 02:42:12 Re-check the batteries. Check the traces from any pins that seem to be corroded from any of those chips or component. Look for any traces that appear to be totally eaten away by the cap goo (pictures would be helpful here). I had a single, solitary trace that was no longer good on mine. Once I ran a bypass wire, it worked perfectly. As for the voltage, early models shipped with soldered, 3V batteries (mine had this). The later versions had battery holders and used 3.6V. Either works just fine; I put holders and 3.6V ones in mine.
Posted by: Falter on 2019-05-22 09:25:08 Thanks muchly. Yeah I am investigating these... I had a similar problem on my Lisa where battery acid had destroyed a whole raft of traces. It's a bit harder for me to see with the Mac II given how small some traces are. It looks like I have some corrosion problems also down by C14-C18. Also will recheck my work on the caps. I've had a fair bit of experience with soldering but these were my first smd. I found it kind of challenging.
Posted by: Falter on 2019-05-22 22:14:44 I was reading this very good guide: https://www.downtowndougbrown.com/2015/03/explanation-of-the-macintosh-iiiix-power-onoff-circuit/ I can see 7V at pins 1 and 14 of UB2, as expected. When I press either of the power buttons, we still get 0V on pin 3 (output). So I've been trying to figure out where things are going wrong.. C3 is not charging up. So I was looking for R2, but all I see are resistor packs... I don't see a separate resistor marked R2.. anyone have any thoughts on how I'd locate that? I'm thinking this failure must be happening very close to that area.
Posted by: Falter on 2019-05-25 20:36:28 I got a bit further - I found a trace that had been eaten through, patched it, now the Mac starts off both keyboard and back power button! Unfortunately, still no video or boot though. 🙁 That indicates to me the possibility of more traces.. but so far I'm not seeing any that are obviously suspect. I will note that while I can power up with the keyboard button, I cannot shut it off with that. Only will shut off with the back power button.
1