Hi Folks,
First post
I'm no electronic engineer, only a keen hack, so I apologies in advance if I ask or say something stupid.
I'm having a problem with a 240v international AB Mac Plus and need some help/advice. When I first got hold of the machine it had no keyboard / mouse meaning other than look at it I couldn't do anything with it. I did however turn the machine on and verified it mostly worked, it had a sad mac memory error, but was alive.
Roll on several months, replacement ram, keyboard etc and now when I turn on the computer the PSU would go into protection, merely clicking. Checking everything over I found that every now and then the PSU would start however the screen continously wobbles horizontally down it's entire length like a jelly in an earth quake!
The AB hasn't had the easiest of lives having obviously been in a damp environment for some time, a fair amount of under mask corrosion is present on the tracks and at some point a battery had leaked destroying the holder but little else.
To tackle the issue I've done the following so far:
/ Cleaned the board
/ Re-flowed pretty much every joint
/ Replaced all the electrolytic caps, using a poly replacement for the NP
/ Continuity checked all potentially bad taces
/ Tested the mainboard in another Mac Plus, OK
With these steps done the Mac now powers up 100% of the time and works with no issue, the screen is bright and focused but is still a wobbly jelly. I've tested the voltages, 5V is spot on 12v is at 12.2 and -12v is at -11.48 and all are stable. The wobble could be @ 50Hz, hard to tell though.
I'm now at the end of my limited knowledge on where to look next. Some reading suggests a possible FBT issue, others suggest the opto coupler and someone kindly suggested an issue with 'clamp' diodes, which doesn't mean a lot to me.
Any advice, pointers greatly appreciated.
First post
I'm no electronic engineer, only a keen hack, so I apologies in advance if I ask or say something stupid.I'm having a problem with a 240v international AB Mac Plus and need some help/advice. When I first got hold of the machine it had no keyboard / mouse meaning other than look at it I couldn't do anything with it. I did however turn the machine on and verified it mostly worked, it had a sad mac memory error, but was alive.
Roll on several months, replacement ram, keyboard etc and now when I turn on the computer the PSU would go into protection, merely clicking. Checking everything over I found that every now and then the PSU would start however the screen continously wobbles horizontally down it's entire length like a jelly in an earth quake!
The AB hasn't had the easiest of lives having obviously been in a damp environment for some time, a fair amount of under mask corrosion is present on the tracks and at some point a battery had leaked destroying the holder but little else.
To tackle the issue I've done the following so far:
/ Cleaned the board
/ Re-flowed pretty much every joint
/ Replaced all the electrolytic caps, using a poly replacement for the NP
/ Continuity checked all potentially bad taces
/ Tested the mainboard in another Mac Plus, OK
With these steps done the Mac now powers up 100% of the time and works with no issue, the screen is bright and focused but is still a wobbly jelly. I've tested the voltages, 5V is spot on 12v is at 12.2 and -12v is at -11.48 and all are stable. The wobble could be @ 50Hz, hard to tell though.
I'm now at the end of my limited knowledge on where to look next. Some reading suggests a possible FBT issue, others suggest the opto coupler and someone kindly suggested an issue with 'clamp' diodes, which doesn't mean a lot to me.
Any advice, pointers greatly appreciated.
