Installing a CPU upgrade for my STE

[VMSZealot]

I think that I may have broken my poor STE. It was unstable - often it would work, often it wouldn’t - bombing when running a memory test, or when accessing a floppy disk. Oddly, it seemed to be happiest when running games (either from floppy or from a gotek), but try to do anything in Gem and you’d get 3 bomb icons. RAM test in TOS 2.06 would usually succeed - but sometimes it would give me three bombs and a 4 (when 4MB RAM was fitted). Changing to 2MB RAM just changed the number to 2. Swapping SIMMs, replacing with entirely new SIMMs? No difference.
Fine. Possibly an unstable power supply? So I fitted a new PSU bought from the fine folks at SidecarTridge. Testing unloaded, it did produce all the correct voltages. Lovely and stable. Alas, it made no difference at all. Fine. Remove the upgrades. And…
Now the STE is dead. Power on and I get a white screen. Nothing else. I’ve broken something. Help me someone! What’s gone wrong? What can I try next? And does anyone here want to earn some money by fixing my f’up for me. I’m clearly out of my depth now.
My STE only has sockets for the 68000, and the ROMs. The blitter, DMA and whatnot are all soldered down - so I’m pretty sure that loose connections are not the problem. And the floppy drive works fine for games, so I don’t think it’s a floppy fault either. But I am at a total loss.
So… When the laughter dies down, and the wise heads here have stopped slapping their foreheads in wonder at the idiocy that I’m displaying, what are the next steps? What do I do next?

[rubber_jonnie]

If you visit 8bitchip.info there are a ton of converted games that all run under TOS 2.06 without compatibility issues.

There is a lot of stuff out there that's been 'fixed' so you're probably going to be fine.

[exxos]

Now the STE is dead. Power on and I get a white screen. Nothing else. I’ve broken something. Help me someone! What’s gone wrong

Does pressing the reset button work?
Also check you not bent any CPU pins, they only need to be a tiny bit out and it won't contact properly.

[rubber_jonnie]

Oh, I somehow missed the post it was dead...

So I understand you've removed the upgrades is that correct? Did you remove all the upgrades or just the CPU upgrade. If it's the latter you should return the machine to stock configuration before trying any troubleshooting, so fully pre upgrade status.

A plain white screen usually indicates a ROM problem, so I would start by looking there for bad connections etc.

However I would also suggest that since you've been doing things to the CPU socket there could be bad contacts there so you may want to follow my guide about adjusting the pins in the PLCC socket for the CPU: PLCC contact tweaking.

However it is also possible that all the activity has caused something more serious to happen. These boards are mechanically fragile and pressing down on the board causes flexing which can fracture the VIAs connecting tracks on the top to tracks on the bottom. This happened to me on a Mega ST which is why I recommend removing the board completely and placing it on a flat surface with a piece of cardboard or similar underneath so the board doesn't flex whilst pushing in the upgrades.

Do you have a diag cart? That may help, but in all honesty I really suggest you start by pulling all the upgrades and looking at the CPU and ROM socket connections first.

[VMSZealot]

Agreed - I fully removed the motherboard from the shell, putting the board directly on a cutting mat which is directly on the work surface. So I don’t think any traces have been broken (because flexing has been kept to a minimum. The exceptions to this rule are when inserting SIMMs, and when connecting power and keyboard connectors. I have returned the board to stock, more or less - the patch wire that I installed for the CPU upgrade is still connected - but not currently connected to anything at the other end. I mean, I suppose it could be screwing things up by acting as an aerial. But it seems unlikely.
It’s very frustrating!