Hi All,
I got a Mac Plus which was in pretty bad condition. The previous owner was trying to fixed it, but was looking in all the wrong places. I managed to mostly restore it, but one final issue, the screen is extremely stretched. Has anyone seen this, or has any suggestions?
Here is a side by side comparison of the stretched screen vs a regular screen:
As you can see, the screen is about 2x stretched. I tested the inductance on L2 and it matches that of a working board. Adjusting the pot on L2 doesn't seem to have an affect on the width.
One hint seems to be when I turn the machine on, for the first several seconds, the bulb at NE2 lights bright, which is not expected. According this, the bulb indicates there's a power surge at J2-9, the CRT cathode, but as I mentioned, only for the several couple seconds. Not sure if this is related to the width issue, or something seperate.
About the Mac Plus. It's beige (not platinum) color, so it's one of the very early ones . Has "Not for resale" graffiti on the side
The logic board is a Rev D, so not the original. Someone did a very poor job of replacing one of the ICs into a socketed one (no flux, scratches everywhere, and a jumper wire). The logic board ended up having bad ram, I replaced the ram and verified it works in a separate Mac Plus.
The analog board on the other hand has had some serious work done to it. Date code is week 29, 1986, so it does seem to be the original. However the flyback seems to have been very cleanly replaced to a 157-0042C. U1 and U2 have also been pulled and replaced with socketed chips. But capacitor at C1 was still the original! When I first booted, I had a 5cm tall vertical on the screen. Upon further inspection, C1 was leaked and L2 had cold soldier. So someone went though the trouble of replacing the flyback and 2 ICs (as well as who knows what else), but never check for cold solder at L2, the most common failure on these. Probably pre-internet era repair. Replacing C1 and fixing the cold soldier I get the double width screen, which is where I'm at right now.
I've ordered the remaining replacement capacitors, but I doubt it will fix the width issue as other capacitors look ok. Anyone have any additional suggestions as I wait for the parts? I checked most of the components in place against a working board, everything seems to be in line so far. I've also ordered the two replacement ICs as I don't trust the ones that were put in since they're already socketed so an easy replacement test.
I got a Mac Plus which was in pretty bad condition. The previous owner was trying to fixed it, but was looking in all the wrong places. I managed to mostly restore it, but one final issue, the screen is extremely stretched. Has anyone seen this, or has any suggestions?
Here is a side by side comparison of the stretched screen vs a regular screen:
As you can see, the screen is about 2x stretched. I tested the inductance on L2 and it matches that of a working board. Adjusting the pot on L2 doesn't seem to have an affect on the width.
One hint seems to be when I turn the machine on, for the first several seconds, the bulb at NE2 lights bright, which is not expected. According this, the bulb indicates there's a power surge at J2-9, the CRT cathode, but as I mentioned, only for the several couple seconds. Not sure if this is related to the width issue, or something seperate.
About the Mac Plus. It's beige (not platinum) color, so it's one of the very early ones . Has "Not for resale" graffiti on the side
The logic board is a Rev D, so not the original. Someone did a very poor job of replacing one of the ICs into a socketed one (no flux, scratches everywhere, and a jumper wire). The logic board ended up having bad ram, I replaced the ram and verified it works in a separate Mac Plus.
The analog board on the other hand has had some serious work done to it. Date code is week 29, 1986, so it does seem to be the original. However the flyback seems to have been very cleanly replaced to a 157-0042C. U1 and U2 have also been pulled and replaced with socketed chips. But capacitor at C1 was still the original! When I first booted, I had a 5cm tall vertical on the screen. Upon further inspection, C1 was leaked and L2 had cold soldier. So someone went though the trouble of replacing the flyback and 2 ICs (as well as who knows what else), but never check for cold solder at L2, the most common failure on these. Probably pre-internet era repair. Replacing C1 and fixing the cold soldier I get the double width screen, which is where I'm at right now.
I've ordered the remaining replacement capacitors, but I doubt it will fix the width issue as other capacitors look ok. Anyone have any additional suggestions as I wait for the parts? I checked most of the components in place against a working board, everything seems to be in line so far. I've also ordered the two replacement ICs as I don't trust the ones that were put in since they're already socketed so an easy replacement test.
