Hola!
Facts:
PAL SNES.
Switched with 50/60Hz switch.
No other mods.
Uses RGB via SCART.
UK TV capable of NTSC and PAL at 50Hz and 60Hz.
Problem:
Intermittently, the video will start to flicker. It manifests itself as the video signal all still being there but with white flickering overlaid. Sometimes it doesn't do it at all. Often it gets worse until the SNES goes into a constant reset mode. Flicker rate is different in 50Hz and 60Hz. Gets worse if I plug anything more than a cartridge into the top i.e. an AR cart or if I plug a copier into it it tries to read the disk but then constantly resets, both of which I presume are due to the extra current being drawn through the cart slot, but it's got to the point where catridges often don't work either.
When it's resetting it doesn't stay reset as if the CIC was missing, it just resets about every second.
Anyone got any ideas?
You said you have a copier ?
Maybe the copier damaged the 7805 chip (voltage regulator) with overcurrent ?
I suggest you taking apart your unit and checking the power supply region in it. Also check the power adapter or try to test the SNES with another power adapter/wall plug
A good hint for power problems is a "humm" noise on the audio
There might be also digital problems or even corrosion on the board. Can you screenshot the SNES while it's shwoing the problem ?
It has no hum and the PSU seems fine.
With regard to voltage, I have a multimeter, what am I looking for?
No problems on the board and it's impossible to screenshot it because the natural tv flicker on a photo distorts the problem :)
i'm assuming you have an official power cable, correct?
Yep, official PAL power brick into a PAL console.
Nothing loose inside and I've given it a good blast with the can of air.
The PAL power brick is AC, right ?
Just mention that connecting it on a Super Famicom is a really bad idea (not that it will burn or anything, it just won't be able to draw the current properly because it has only a half cycle rectifier on the input and the PAL SNES has a full diode bridge with 4 rectifier diodes)
Can you provide us some screenshots ?
Yes, I know the differences between the three power supplies. It's a PAL SNES using a PAL adaptor.
Pictures don't serve as any indication because you can't see the flickering past the fact that the TV shows up flickery on the camera anyway. I couldn't get it to actually show what was going on.
Seems to me like there's a white bar (about an inch thick on a 32" diagonal TV) that rolls quickly down the screen over and over. Sometimes it goes very slowly, but resetting is worse when it goes quickly and when there's more plugged in the top, but sometimes it'll reset with a basic game with no special chips in too.
I've tried a different connection method including composite and another RGB cable.
my MD2 once had a bit similiar issue... it was on a BIG speaker, and vibration caused one chip to be half loose from the board... some 20mins to resolder 208 pins of one chip and problem was gone.