I have an A600 Rev 2D (schematic), which is dead as a doorknob. It was that way when I acquired it some years ago, and it's mostly been in storage since.
Between the 5V rail and GND I measure a low resistance, only around 115 to 140 Ω, and that doesn't seem right. Removing all the electrolytic capacitors did not help. There has been some slight electrolyte leakage from the 10 μF caps, as evidenced by a fishy smell when I desoldered them, but no visible corrosion on the board. After removing the caps, I cleaned the surrounding PCB areas with isopropyl.
Unloaded, the PSU gives out all the right voltages, and it works fine with my A500.
When I connect the PSU to the A600 motherboard, the 5V rail drops to near zero. I have tried feeling the temperature of the chips while they're powered, but nothing gets noticably hot. Maybe the PSU goes into some safe shutdown when it sees overcurrent?
I feel kind of stuck at this point, all I can think of is to start desoldering chips until the short disappears. But that seems like a ham fisted approach.
Has anyone experienced similar symptoms? Any tips on how to continue troubleshooting this problem?
I tried the alcohol test. I set the current limit to ~1A, which limited the voltage to a bit over 2V.
Agnus, Denise and both of the CIAs dried up somewhat quickly in the center, but that I suppose is to be expected.
But the DRAM was acting odd: U17 (which is optional according to the datasheet) stayed cool, while U16 (which I suppose is the main DRAM chip then) dried up very quickly.
U22, which is a 74LS245 octal bus transceiver also dried somewhat quickly. While U21, also a 74LS245, stayed wet. Both of these sit between the CPU and the DRD bus (DRAM Data Bus) that goes to Agnus, Denise, Paula, and both DRAM chips.
Not sure what to make of it all yet. Perhaps I should increase the current to 2A to really see the effect, but I'm afraid of cooking something that shouldn't be cooked.
I guess my primary suspect at this point is the U16 DRAM chip.