This is an Assy no. 250469 Rev. A short board. The machine would boot normally and then within 30 seconds the screen would look like the one below with a ready message and no blinking cursor.
When I touched the different chips on the board, I noticed that the SID chip (MOS 8580R5) got extremely hot. When replaced with a working SID, the machine was brought back to normal operation and the temperature of the replaced SID was normal.
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Thanks for these repair reports! Will surely be useful for anyone with a broken C64. I just maintenanced a C64 for the first time ever, although only to cleanse it as it was in a totally unacceptable condition – all grime inside out and smelled like a bottle of 30 years old parfume mixed with Coke.