hey guys. I have my Platinum IIe, and I absolutely love it. It is helping me improve my basic (something I have not used since my dad's Atari 800, which he still has, just not the basic cartridge). Anyways, my ideal setup when I originally got this beast, was to hook it in to my Apple M4551 blueberry LCD. The video input jack on the back (a standard yellow RCA plug) is already occupied by my PS2. So, I dug out an old RCA splitter, plugged in my PS2 to one, and the Apple II to another. But when I fired it up, all I got was a single white band horizontally across the screen. I thought "maybe the splitter can only carry audio signals), but I fired up my PS2 through the splitter, and got a crystal clear picture. So, I unplugged the splitter, and plugged the II in to the monitor directly. Same issue.
Please note that before and after I did this, I hooked it in to our DVD player, which works. I get a good picture, however I would like this out of the way of my parents, and in a environment where I can tinker.
I have also tried hooking it to my old 13" TV. the TV only has coax, but I have this old Radio Shack TV/Game switch (the model number escapes me, but it is no longer sold by rat shack). It has an RCA jack labeled game, a coax and those screw plugs, and auxiliary screw and coax jacks. It also has a switch one side TV, one side game. I hooked up the coax, and hooked the II to the game port. Upon switching to channel 3 and flipping the switch, I only get interference, but what is interesting is pressing command-reset on the II (which usually brings up a prompt), I get a different pattern of interference on the TV. I have also tried hooking in the screw connection, but the same results.
any ideas? These two are my ideal setups, the monitor more so, because it is in range of the B&W for the Apple II game server.
thanks.
-digital 
The output from your Apple II is composite video. It's not modulated to a TV channel. (Unlike the output from most contemporary home computers, like the Atari 800/XL/XE series, Commodore 64, whatever.) All that switchbox does is disable the antenna/cable feed into a TV and substitute the *modulated* output from a game console in its place. You can't use it to hook an Apple II up unless it's also fitted with an external RF modulator.
As for the problem with the LCD monitor, well, all I can note there is the composite video output from Apple IIs isn't really "according to Hoyle" NTSC standard. It's not unusual to encounter problems when hooking it up to non-CRT monitors.
I'd suggest finding an original Apple-brand color composite monitor, if possible. Apple tweaked those so 80 column text was actually "readable", which it generally isn't on televisions. My second best suggestion would be getting a newer CRT television with a composite input jack. If you pay more then $10 for one at a garage sale you're paying too much.
(Edit: The third suggestion I'd make, if you want to *try* to make it go on the LCD *or* make it go on the TV, is find an old VCR. Connect the Apple to its composite input and tune to it, and try the composite output on the Apple LCD monitor. It's possible that there's something electrical it doesn't like about the Apple output that "filtering" it through the VCR will fix. You can of course also use a VCR as an "RF modulator" by hooking its coaxial cable output to the TV set, but I'd recommend against doing that simply because RF modulation so negatively impacts the picture quality. 80 column text will be completely hopeless.)
--Peace
Panasonic made a composite color/B&W monitor years
back for use with early computers and CCTV systems.
I use one with my Apple //e occasionally to game in
color. These can be found ususally at ham-fests and
thrift stores. There are newer ones out there, but
I am not sure as to the signal inputs, so you might
be back at 'square-one' and looking for a RF mod.
Try checking on "A2Web" in the Classified Section
and post a "wanted" ad.Don't forget our Buy/Sell/
Trade thread here as well.
Personally, I'm getting ready to try a DVD/LCD hack
for my //e.
Good luck. Keep us posted.
Also refer to my comments on the thread here
discussing "unknown Apple monitors" listing
several alternative monitors that can be used.