Adding a CRT toggle switch

[jcs]

I'm going to be using a Mac Plus as a BBS server and would like to be able to turn the CRT off to preserve its life, conserve power, and avoid having a display on in my office 24/7.

Would this even work? Can I just put a toggle switch inline with power to the flyback transformer or does something more complicated need to be done?

 

[Kai Robinson]

@techknight might be able to help here - he's something of a CRT guru

 

[AndyDiags]

You would probably need to disable the horizontal, vertical, and video circuits. Surely possible, but will require multiple modifications.
You should consider using a Macintosh II instead, such as the Macintosh IIci. Same architecture, and you can connect to LCD or a one of those portrait monitors if you have the space.

 

[davidg5678]

I found this thread on the 68kMLA from a few years ago: https://68kmla.org/bb/index.php?threads/mac-se-monitor-on-off-switch.34998/#post-377850

 

[rjkucia]

Dumb question - can you just turn the brightness knob all the way down? When I do that on my SE it looks like it's completely off.

 

[Elemenoh]

Dumb question - can you just turn the brightness knob all the way down? When I do that on my SE it looks like it's completely off.

I think the heater would still be on, so less efficient and adds to wear and tear.

 

[Volvo242GT]

You would probably need to disable the horizontal, vertical, and video circuits. Surely possible, but will require multiple modifications.
You should consider using a Macintosh II instead, such as the Macintosh IIci. Same architecture, and you can connect to LCD or a one of those portrait monitors if you have the space.

View attachment 2941

Another option is one of the LC/Performa 4xx series Macs... Uses less energy than the IIci, and should be adequate enough for BBS duty. One of those with the 12" Macintosh RGB display isn't much bigger than an SE or a Classic... An LCIII with FPU would be somewhat equivalent to the IIci, performance-wise. Less expandable, but, probably not that necessary to run a BBS. Mainly need a large hard drive for files, and a network connection.

 

[techknight]

You need to cut the Sweep 12V completely off to the analog board.

Even if you cut the drive signal to the horizontal output stage, the filament will always stay on and cook which will wear the CRT down.

Best solution is to cut the 12V sweep entirely to the analog section. What I do not know though, is if turning that back on would cause a surge-current spike in the PSU which would trigger a spontaneous reboot.

 

[Bolle]

Can't you just cut out the HSYNC signal from the logicboard? No Hsync, no HV and as heating voltage and everything else are received from separate flyback windings it should all be shut off, shouldn't it?

 

[techknight]

I would have to look at the schematics again, but last I checked, the heater is powered directly from the sweep voltage on those compacts.

 

[techknight]

Yes, I am correct:

To totally power down the CRT Section of a Compact, you must cut the 12V sweep supply.

What would be totally cool is finding an unused signal on one of the VIAs, a transistor, relay, etc. and then writing an extention to allow the monitor to go into "energy saver" but ya know. haha.

 

[Bolle]

Yep, you're right, filament is powered right from 12V.

 

[techknight]

Yep! So you must cut the 12V (red) sweep supply.

However the caveat is, I dont know if this will cause a surge current condition which can trigger spontaneous reboots when turning the CRT back on. So maybe a capacitor pi filter network between the switch to attempt to suppress this. the CRT filament draws a TON of current when first energized because it is cold.

 

[techknight]

I got an old clunker SE sitting around that I could experiment with this, but who knows when I will have the time to get to it. I am literally buried with other projects including rebuilding an ANS power supply that died.