Hey All,
I've just received a 6128 to repair off of fleabay and whilst it had most of the DRAM's dead (which have now been replaced), I have got it working again - albeit with a small issue..
When powering it up with 5v from my bench supply, it will draw around 900mA but not come on - just a black screen. When I check the VCC pins on the logic chips etc, they're all down at about +3.1v...
If I up the supply voltage to +5.9v, it will come on and appear to work fine - all chips has around +4.1v - nothing getting warm except the AY and the CPU (RAM just barely warm)..
Is this strange? I've repaired a couple of 464's in the past and don't remember them needing almost +6v to get 'em working..
I've replaced all the electrolytic caps on the board with no change..
Reading about 500R between the power socket VCC and GND pins.. which also makes me wonder if I have a short somewhere?
Any insight would be appreciated!
Mark.