I'm not sure if anybody would be able to help, but I am trying to find some voltage readings from an Apple ][e PAL version. Specifically I am after voltage readings from the TCA 650 (UA13) that forms part of the video circuit, and specifically I need voltage readings from:
- Pin 14 - Power in. According to the PAL schematics I have, plus what the TCA 650 datasheet shows, this should be 12v. I'm reading 5v.
- Pin 4 - When the colour killer switch is off, it is open and pin 4 reads 2.5v-2.7v on mine. The datasheet states for PAL to be selected it should be 7-12v, and there is a contradiction here with the schematics that show 5v to pin 4 with the switch open. I suspect that the 5v signal may be enough to make it run fine, but since mine is half that, I can't help but think there is some sort of power issue, maybe a short somewhere or the PSU is falling short.
What I'd like please if you can help, are voltage readings from both of these pins with the machine booted and the colour killer switch turned off. Please note this MUST be a PAL machine as the NTSC machine has a very different video circuit.I have a suspicion that the reason that my colour display is turning off intermittently is because the voltage at pin 4 is somewhere in between the 0v-1v required for SECAM (Mono) and the 7v-12v required for PAL (Colour).The Colour mode will either go off or flicker between that and Mono, almost like the signal is floating. I will check my own machine with the TCA 650 removed to see what the voltages are like in case it's marginal and pullng them down. I would add that when the voltage reaches the higher end of the scale, so 2.7v, it is more stable, but once it drops to the lower end, that's where the mode switching occurs.
Any help would be gratefully received.