For other future cases like this, I've been struggling with a similar issue for a long time - known working trapdoor memory expansion not being recognised - so stuck on 512kb. First i had grey screen on boot. I removed a jumper on my expansion to configure as chipram and got yellow screen on boot. I noticed that the rev5 motherboard had been modified...jp2 jumper had been soldered such that the top 2 pads had been joined and the trace to the bottom pad (originally joined to the middle one) had been cut. This seemed like a previous mod to set an expansion to chip ram. However, i read that i needed an agnus 8372 - and the board had an 8731. I guesses that had been sold and replaced with an 8371. I restored the original jo2 jumper setting - but still yellow screen on boot. So i spent an hour after finding various threads including this looking for a trace that had been cut. I noticed a bad sder joint on one of the trapdoor expansion pins underneath the board. I soldered it - and voila - the memory was accepted - working fine. I think the mod on my board was to remove solder on one of the trapdoor pins underneath the board. Hope this helps someone
