> I was recently given an SX-64, an old Commie 64 portable
> Questions:
> When I turn it on, I get an illuminated, but empty screen. If I
> change any of the hardware (KBD), and turn the machine on again,
> I get a screen filled with gibberish. Upson subsequent resets,
> the screen remains blank, until I change the hardware config,
> at which point I will again get a screen of gibberish upon
> reboot.
A failing PLA chip can do that. I think the time the computer is turned off
gives the chip a chance to cool a bit and start working... almost. A bad
PLA is the most common failure because it runs very hot normally. You can
swap a PLA out of a working C64 to test it.
> Also, I notice the video output on the back... is that S-video?
> If not, what format is it?
It does output S-video, and composite video too. You need the correct
cable, of course. Here is the A/V connector of the SX shown facing the rear
of the computer:
no connection -----8
7-----no connection
6---------chroma out
audio out -----3
1----- luminance (B & W signal)
audio in -----5
4----- composite video out
2----- ground
S outputs would be pin 1 (luminance signal) and pin 6 (color signal). Audio
output is on pin 3. With a standard video monitor, use pin 4 for video.
>
> I wish to trade the PLA chip from a C64 to an SX-64, to correct
a monitor problem.
Reading the past postings in this newsgroup, I've seen >many conflicting stories of which chip is the PLA. I have located the
chip at U17, but it is not the chip commonly described as the PLA, and >it's serial is 906114.
>The PLA is U17 in the standard C64, and that is the correct CBM part number
(just add a -01).
Also, I can't find the PLA chip on the SX->64 board. Can anyone tell me how I locate both chips on both boards, so I can go about replacing the
one on my sx-64?
It's UE4 on the CPU board (middle of the board), right next to the VIC chip
(the one with the heat sink on it). It could be marked 82S100, 906114-01,
7700-001 or MB112A101. I once had one marked 93459DC.
Ray Carlsen