M1212 Macintosh Color Display no picture

lostkerbal

Active member
I recently acquired a very minty (non-yellowed!) M1212 Display, but it doesn't want to live just yet. I plugged it in, powered it on, and it greeted me with a very dim purple glow (no input). I plugged in a known good VGA adapter, but still nothing. I opened it up and adjusted the pots to get a better look at the artifacting (they didn't change with plugging in/unplugging the input), and it looks like many horizontal/zig-zag bright lines on a slightly darker background. I adjusted the color to make sure all three colors (RGB) were good, and they were, so no green failure for me. But it still won't respond to any kind of input. While on, it is very static-y but no loud hum, and I did not witness flyback arcing. I also checked the board for caps, and all of them look perfect; it's even quite clean. Any thoughts?
 

Arbee

Well-known member
You can diagnose bad solder joints by giving the monitor a mild thump. (Be very careful doing that with the case off though!) If the screen reacts at all from a mechanical shock, there are bad solder joints.

Also, where's the purple glow coming from? A blue or purple glow from the CRT neck means air has gotten into the tube and it's bad.
 

lostkerbal

Active member
You can diagnose bad solder joints by giving the monitor a mild thump. (Be very careful doing that with the case off though!) If the screen reacts at all from a mechanical shock, there are bad solder joints.

Also, where's the purple glow coming from? A blue or purple glow from the CRT neck means air has gotten into the tube and it's bad.
I whacked it every which way, nothing drastic happened, just some wobbling. It seemed to have a strong reaction to adjusting the pots on the back, but I'm unsure if the adapter I'm using is good (trying to see parts of a test pattern). There's no glow from the neck, thankfully, it was just coming from the display itself when I first powered it on; like I stated before, all three guns seem to be working just fine, so it's a control/sync issue. Although, and I have noticed this on my other two (working fine) CRTs, that there is a tiny bit of orange/yellow 'heat' glow coming from around the pins on the rear of the tube.
 

olePigeon

Well-known member
@lostkerbal I don't know if this one has a similar insides as the AppleColor High Resolution display, but mine had a similar issue that was caused by a large coil being loose. The plastic became super brittle and it broke free from the bracket. I repaired the plastic bar with some super glue and secured it with zip ties. This fixed the issue for me. So if yours has a big coil attached to the neck with plastic clips, try poking at the coil, see if affects the sync.
 

lostkerbal

Active member
@lostkerbal I don't know if this one has a similar insides as the AppleColor High Resolution display, but mine had a similar issue that was caused by a large coil being loose. The plastic became super brittle and it broke free from the bracket. I repaired the plastic bar with some super glue and secured it with zip ties. This fixed the issue for me. So if yours has a big coil attached to the neck with plastic clips, try poking at the coil, see if affects the sync.
It looks to be very similar, I'll give that a try; do you have any images or more elaborate descriptions of what/where the coil is?
 
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