IBM 4863 /PCjr monitor/ power supply/schematic

[deanimator]

Hi all,
I'm currently awaiting one of these clunkers and I was wondering if anyone got a complete copy of the schematics, i.e. including its audio amplifier and power supply stage. There's some info on the Web which states that these monitors are internally similar to an IBM 5153, which has a PSU that works on both 120 and 230 volts AC with an automatic switchover. On the back-side of a 4863 though, there's only 120 volts AC input, which can make sense as I'm not sure if these machines ever made it over the pond.
In the PCjr technical reference, there's only a schematic of the guts driving the screen, which looks more-or-less identical to the schematic of a 5153.
I guess even if that thing lacks the dual voltage switchover, it could run with some series capacitive reactance straight from 230 volts... I won't tell anyone. And since it's a direct-drive, I guess it doesn't matter if the mains AC is 50 or 60Hz since there will be some kind of a rectifier. If anyone could have a look that'd be greatly appreciated.

Thanks

 

[rlumsden]

Here's some info and a poor scan of the schematic.

 

[Acorn]

FYI...
There is an error in the MONITOR.DOC attachment above.
C402 should be 0.1 µF @ 35v.
...NOT 1.0 µF as it says in the document.

I am certain of this because I removed and measured C402 in my now working 4863. I fixed my monitor by simply reflowing the solder on the flyback transformer and the CRT socket on the neck board. No components were bad.

Interesting enough, there is a handwritten note in the upper left corner of the attached schematic that says C402 is 0.1 µF.
Sure wish I could find a better schematic somewhere!

 

[mikey99]

Attached is a more readable schematic. The original is way too large for my scanner so I took a few photos with my phone.

 

[Acorn]

Thanks Mikey99. That's a big improvement.

 

[fsimoes]

Can someone please help me with the external pinout for th epower supply? I dont have the external brick and can not find what voltage is supposed to be at pins 1,2,3 (only found some comment about being 18 VAC)

 

[DoctorOctal]

The center pin is ground, and the two outer pins are for AC input at around 15 V or more. The earlier power bricks are rated at 16.7 VAC, 56 VA, and the later ones are rated at 17.7 VAC, 75 VA. When not connected to a load, the voltage will read about 18 or 19 VAC.

The original brick provides AC, but in principle you could also use DC (and the polarity wouldn’t matter). I’d use at least 16 VDC to provide sufficient margin. That said, if you have the earlier, short board PSU (that doesn’t extend much past the edge connector), you might slightly exceed the power dissipation rating of its rectifier diodes by using DC. On the long board PSU (that extends from the back to the front of the chassis), you have more latitude because it’s designed for higher power and has the rectifier bridge heat-sinked (though I don’t know the power rating of the bridge off-hand).

 

[DoctorOctal]

Of course, the easiest option is just to get an actual PCjr power brick. Contact me through my Web site if you want one.