> I was recently given an SX-64, an old Commie 64 portable
> 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
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
audio out -----3 1----- luminance (B & W signal)
audio in -----5 4----- composite video out
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.