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That 7MHz wire might actually be the cause - that's an antenna, depending on how you've soldered it. The ACA500plus does not need that, as it only looks at clock signals that are available on all revisions of the A500.
Also, if the Rev.5 Amiga is in it's original form, it has the OCS Agnus. Is that PAL or NTSC?
what does the burgandy/dark red screen mean?
I'd have to see if there are other things that the card communicates. Have you tried doing a keyboard reset after an unsuccessful power-up? If that works, then the reset circuit of the A500 Rev.5 may not be reliable any more.
are there any extra pins/bus connections/pins at the a500 side are used when you plug in a 1200 accelerator to the Aca500plus.
Maybe an issue with one of those?
No, not a single one. The A500 shouldn't notice the difference on the bus side.
The one thing that's different is that the A1200 accelerator adds a pull-up resistor to the reset line - this can be measured and may make a difference, but normally on the positive side (I don't add these resistors for no reason!). That's R7, between the 150-pin connector and the CPU. All other signals are generated by the ACA500plus logic.
If you write "loops round" - does that mean the animation on the DisMo? If so, the CPU is running already, as this animation is uploaded into the DisMo by the early menu code. You might get more information through serial debugging: Put a nullmodem cable between the A500 and any other computer, switch serial debugging on in the global menu (I think - off the top of my head), and use 115200/8N1 as serial setting (no handshake; the Amiga will just send). We may get an idea where it hangs from the serial output.
ive done some more work this morning
firstly removed the wire mod for the 6mhz signal to expansion bus
still red screen
removed trapdoor expansion and floppy drive
still red screen
Went and got my a1200 out of storage...
took the aca1232 out of the a1200 plugged into aca500plus
works first time every time
put the aca1221lc into the 1200, red screen!
issue with aca 1221lc...
had a look around board for any bent pins , bad solder etc
nothing in particular although some ugly looking solder and flux on cpu connection
cleaned aca1221LC board and connectors with 99% isopropyl
plugged back in worked first time 
so answer something on aca1221lC was not right
in other news, my new CA-PSU appears to also allow stable running at 40mhz...previously it would halt after a couple of minutes
so answer something on aca1221lC was not right
Funny that it seemed to be the A500 revision at first.
in other news, my new CA-PSU appears to also allow stable running at 40mhz...previously it would halt after a couple of minutes
That's known - CPUs are way more stable when power is within spec (not just voltage, but also ripple). Many customers have replicated this. The ACA1221lc is surprisingly fast at 40MHz - almost as fast as a 68030@33MHz.
sadly lacking the 128mb though....
I can only build with what I have, and 68ec020 CPUs only have limited address space. While they are full 32-bit CPUs on the inside, they only bring 24 address lines to the outside world, so 16M address space (like the 68000 CPU) is all we can work with.
There are versions of the 68020 CPU that have the full 32-bit data bus like the other CPUs, but they are just not available on the market (at least not for a good price compared to 68030 CPUs).
ACA600 is next on the list - and it's going to be good!
worst of all the amiga models
...which needs to be improved
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