A4000D wont boot with riser card installed

[shadowrider]

have an a 4000ec/030 than reciently accuired that boots fine without the riser card, have a hd floppy and cd-rom running with 3.1 roms, all boots fine till i add the the riser card then i get a yellow screen and the power light blinks rapidly the nothing.. have looked for a short but dont see any, not sure where too proceed from here, help is appreciated,
 
d.j.obrien@cox.net
Shadowrider on irc #amigaworld

[Crom00]

If I remember correctly in both the a3000 and a4000D there was a piece of PVC plastic that was supposed to go behind the backplane board. It's purpose I believe was to prevent a short that would cause strangeness like no startups or freaky colors on screen.

[Cosmos Amiga]

Old capacitors... again and again !