EPL Cartridges jammed in HP5550dtn

I cannot take out the EPL toner cartridges in my HP5550dtn printer. This is a new phenomena as the printer is out of maintenance contract. All four cartridges appear to be jammed. Unfortunately there isnt any reference to this issue in the workshop manual. I have tried several ideas to release the cartridges eg. Switching the printer off. Removing the paper tray. I suspect it could be a broken gear wheel in one of the cartridges but I dont have any staring references to release the units. Can anyone advise me on the way to release the system.

Question by Shalbo on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.