For sales purposes, I had a professional replace 9 Pismo PC750 400MHz CPU daughter cards with PPC7410 500MHz chips.
Five of them were PC750s that were originally working normally, but the other four did not start even if the PRAM battery was removed, as mg.man said.
My Pismo, which works fine except for the CPU daughter card, doesn't work even after I remove the PRAM battery. At first, I thought that the CPU chip was bad, and that it would start up if I replaced it with a PPC7410 500MHz chip. I thought so, but the 4 faulty cards that were returned to me were still faulty.
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So, I bought a normal PC750 400MHz CPU daughter card at an auction and tried replacing the ROM chip. (I used the same type of low temperature solder as ChipQuik for removal)
Pismo (PPC7410 500MHz) started successfully. (Of course I changed the chip resistance settings on the card)
When I ported the ROM removed from the first card to the second "faulty PPC7410 500MHz card," it started working as well. (wonder!)
After repeated porting in this way, out of the four defective CPU daughter cards, only one did not start up until the end. As a result, I ended up with a total of 8 Pismo (PPC7410 500MHz) daughter cards.
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If the results are not good even after following the advice of others, you may want to try replacing the ROM chip.
The method to replace this ROM was inspired by this 68KMLA forum's post about Color Classic repair.