Gubbish, congrats!
Before you do any more work with that unit powered on, make sure you check the voltage and adjust for optimal conditions. Having cleaned it up, it will give you a false sense of security, and could easily tax the aged and poorly stored components to a literal melt-down. This is especially true if you are going to keep testing with it. Turning the unit on is one of the more stressful functions you can perform, so it's no wonder that they often fail on startup more than any other time.
As for the ROMs, look forward to hearing if either of the originals now function, which now that the DRAMs have been restored, might actually work. Good trouble-shooting by the way. I presume you checked the ROM pins for corrosion and found none? Regardless, I can't say I'm surprised the large Apple silkscreened logo DRAM chips were bad. This is the most common failure in logic boards with those chips. This might explain why Apple got such a deal on them! Otherwise, I have found the logic board components to be quite robust. I am a bit surprised that the ROMs have gone bad, but like the DRAM Apple sourced those out to more than one manufacturer, like the CPU as well. So your particular ROMs could likewise suffer from some form of "bit-rot" especially if stored poorly. Since I have not yet heard an explanation for why this kind of failure occurs, I am free to speculate that environmental factors can contribute just as much as disuse. But what do I know.
Thanks for offering such a detailed path to recovery. It just goes to prove how easy it can be to recover these little guys. Since you are now running mixed DRAMs, I am quite interested in how the Mac operates once you get it completely back on it's feet and using it.
Before you do any more work with that unit powered on, make sure you check the voltage and adjust for optimal conditions. Having cleaned it up, it will give you a false sense of security, and could easily tax the aged and poorly stored components to a literal melt-down. This is especially true if you are going to keep testing with it. Turning the unit on is one of the more stressful functions you can perform, so it's no wonder that they often fail on startup more than any other time.
As for the ROMs, look forward to hearing if either of the originals now function, which now that the DRAMs have been restored, might actually work. Good trouble-shooting by the way. I presume you checked the ROM pins for corrosion and found none? Regardless, I can't say I'm surprised the large Apple silkscreened logo DRAM chips were bad. This is the most common failure in logic boards with those chips. This might explain why Apple got such a deal on them! Otherwise, I have found the logic board components to be quite robust. I am a bit surprised that the ROMs have gone bad, but like the DRAM Apple sourced those out to more than one manufacturer, like the CPU as well. So your particular ROMs could likewise suffer from some form of "bit-rot" especially if stored poorly. Since I have not yet heard an explanation for why this kind of failure occurs, I am free to speculate that environmental factors can contribute just as much as disuse. But what do I know.
Thanks for offering such a detailed path to recovery. It just goes to prove how easy it can be to recover these little guys. Since you are now running mixed DRAMs, I am quite interested in how the Mac operates once you get it completely back on it's feet and using it.