Originally Posted by jerrymc
For the record, I installed a 6.4a image from my HR10-250 in my Dad's Series 2 DVR40 and it's been stable for a couple of weeks now.
The 6.4a for the HR10 is a little bit different, but will work on standard series2's. There are minor differences, that I think are dependent on hardware features only present in the HR10. If you press the window/aspect button on the remote, it will display on the screen panel or full display modes, but the presented display will not change. There will be options for digital closed captions, but if you turn them on, they will not work. If you attempt to access any menus pertaining to the OTA antenna input (which is absent on your box), it usually causes the system to reboot.
I've got a box like that that has been running the HR10's version of 6.4a for years. It has an occasional unexpected reboot, but I attribute that to it's nearly full 2TB drive, and/or the possibility of the power supply in the 10 + year old box may be nearing the point of needing new capacitors.