1200XL Questions

[+Larry]

What is the purpose of the vertical "choke" (L11) on the 1200XL mobo?  Is it audio related or video related or something else?  Google shed no light on this.

 

Can the 800XL major IC's be swapped in for the 1200XL equivalents?  (I know about the replacement with the 800XL rom.)

 

Thanks,

Larry

[Rybags]

Sobola schematic shows it part of the AV circuit though they've been known to have errors.

The major ICs - CPU and 3 custom chips + PIA are the same.

MMU is different.  OS has the lo/hi Rom where 800XL has just the single.

 

Fairly sure there are mods around to allow use of the 800XL OS and/or MMU, main reason there would be to have internal Basic and/or a PBI.

[+bob1200xl]

The RF modulator feeds an RF signal to a TV tuner. This signal is a modulated waveform that carries the video (0-4.5mhz AM), chroma, (4.5mhz-6mhz PE), and audio (6.0mhz-6.44mhz FM). All of this is sub-carrier on a 90mhz transmitted carrier. (ch.2)

 

L11 is the adjustment for the audio carrier at 6+mhz.

 

I think this is right -- pretty close, anyway.

 

Bob

[+Larry]

Thanks, Bob.  I've got one mobo with it removed.  I still have it, so it can be reinstalled, but I don't remember why it was removed.

 

 

[+bob1200xl]

Probably for 7/14 mhz upgrades.

 

Bob

[+Larry]

Is there a good ram tester for a stock 64K 1200XL?  I'm going through boards and I'd like to test them, but most of the testers that I have balk at the 1200XL OS.  Likewise, is there a version of the built-in XL/XE self test that can work with the 1200XL OS?  On a positive note, I found that my keyboards still work good.