Apple IIgs woes - unreadable screen, snow

[sgifanatic]

I started up the IIgs after a few months and was greeted by this:




I reseated the memory card, tried again, same result. Any idea what might be happening?

 

[retrogear]

The horizontal frequency of your crt display is too low. Did you try adjusting the horizontal hold? Looking at the back of the display is three controls. It's the one on the right.

Larry G

 

[dorkbert]

might be your on board battery died and the system switched your display characteristics over to 50Hz.
if that is the case, I suggest that you remove the battery before it start bleeding.

 

[sgifanatic]

Thank you. This was super weird. I left it powered on for a while and it started working. That usually happens with weak caps, but the symptom in those cases is an inability to power up. Not sure what's going on here, but I hope this system isn't about to implode on me...

 

[retrogear]

This might be information overload but the LA7822 chip in the CRT that produces the horizontal deflection has an "xray protect" input on pin 5. If the high voltage increases above a safety threshold, it is designed to lower the horizontal frequency which also
lowers the high voltage. If the horizontal control mentioned previously didn't stabilize the screen then this is the next likely cause. Unfortunately the problem can be many things and possibly a weak cap like you said. Worst case the CRT will just shut itself
off. If it's stable after warmup I'd say use it. Maybe using it will improve it.

Larry G