jpmanz, you have it.
I work a lot-A LOT-with the IQ series, and the 500 appears to be the worst.
The symptom you describe, is seen quite often, and eventually, as HP has no Maintenance and Service guide, created one of my own, by taking step-by-step photos of one I disassembled.
You have to admit, though, that re-assembling one is quite the challenge!