I'm missing something............but what?

[Willum7.1]

Hi. I'm the proud owner of a 24", mid-2007 iMac 7.1 that I've had from new.
No need to tell anyone that, whilst it still works like a dream, it's on El Capitan - and there's no more software updates for it.
So. Decided to follow Dosdude1 and many other folks example and put a SSD and aT9500 CPU in and keep it alive and safe on Catalina.
All worked well until it came to turning it back on with the new CPU installed. The SSD was already up and running perfectly.
The T9500 only presented me with a quick buzz from the optical drive and a very small flick from the CPU fan. No chime, no logo, black screen, nada!
Reinstall the old CPU and away it goes, perfect.

I'm on it now, typing this (and it's a hell of a lot faster!) I've done that CPU swap exercise twice now and the same result.
Is there something I'm missing in the bowels of the poor thing's makeup. It has the ATI Radeon HD 2600 Pro 256 MB GPU but all I can find says it should be OK and I've got a USB WiFi stick ready just in case. I've had various responses saying everything from 'It'll NEVER work' to 'Anyone who says they've done it is at it'.
My alternative theory:
I've got a duff T9500? It was claimed to be 'Opened, Never Used, Tested'................ (how, I wonder?)
Any help with things to check in the 'About This Mac' department, or anywhere else for that matter, would be most welcome.
Will

 

[Pacific1972]

Hmm, it can't be the TDP (35W) and I don't think the TDP peak level was responsible.
Excuse me, I haven't an idea yet...

Perhaps you should sell your machine and buy a newer 21.5" iMac from 2010-2011.
These iMacs have Core i3 / i5 / i7 CPU (Minimum 40% more CPU Power), Full HD
Display and of course more GPU Power...

The 2010 iMac have a Socket 1156 and you can go from i3-540 to i5-680 (3.6Ghz).
Note that these Core i5 is DualCore (4 Treats) but have the same socket and TDP
of 73W. You can buy another 21.5" on ebay, sell the 24" - best reason to become
a newer macOS also...

 

[Willum7.1]

Hmm, it can't be the TDP (35W) and I don't think the TDP peak level was responsible.
Excuse me, I haven't an idea yet...

Perhaps you should sell your machine and buy a newer 21.5" iMac from 2010-2011.
These iMacs have Core i3 / i5 / i7 CPU (Minimum 40% more CPU Power), Full HD
Display and of course more GPU Power...

The 2010 iMac have a Socket 1156 and you can go from i3-540 to i5-680 (3.6Ghz).
Note that these Core i5 is DualCore (4 Treats) but have the same socket and TDP
of 73W. You can buy another 21.5" on ebay, sell the 24" - best reason to become
a newer macOS also...

The thought of buying something newer had crossed my mind - but that was before I'd started down this route. If it cannot be fixed, then that will be my only option.
However: It appears that quite a few people have tried and succeeded with the same hardware and route I've taken, so either:
1. it's Urban Myth (possible but unlikely, considering the number of articles and blogs)
2. there's something wrong with what I have done (quite possibly but certainly not from a hardware point of view)
3. I've got a dud T9500 CPU
What I'd love to do is dispel the Urban Myth theory by contacting someone who's done it successfully and can tell me the exact detail of the iMac 7.1 hardware used, better still the alterations to any software/setup (if) that was done.
Most of all, I'd love to be able to keep using my faithful old iMac.
Will

 

[Willum7.1]

It's NOT an Urban Myth!!
The beast lives again. Got the replacement T9500 CPU and fitted it and away it went with no problems. WiFi works fine, Bluetooth might just have a problem with tethering - but I never use it anyhow. Links OK to my iPhone but claims it cannot connect to the internet through it. The replacement CPU is most certainly a well used item. Claimed as 'Opened, Never Used' it had very hard baked heat transfer paste on it that took serious cleaning to get off. Seller claimed it was because he'd tested it.
In a pig's eye!
Draw your own conclusions but the old CPU I took out of it had baked on paste but that had been in there 13 years.
The paste I put on when it was reassembled with the old CPU in it was still soft after 2 weeks work.

This how the report looks. No mention of exact CPU type or speed and a misreported bus speed. I don't really care, it runs markedly quicker.
Next step will be dosdude1's patcher and Catalina, then I'll be cracking open a beer!
Fingers well and truly crossed. I've been in there so often, I could swap the CPU with my eyes closed.
Will