Hello ld13
My E220 was also moody when I got it mid January... changing colour (mode) to a point of instability.
My eventual resolve was the Huawei software/drivers - after trying Vodafone Mobile Connect - which is a bit better than Lite.
Vodashop actually said I should bring my PC and modem to them and they could install Mobile Connect - not sure which version would work though....
The changing from 3G to HSDPA and back should not be signal related - HSDPA can rather be seen as a mode of 3G. What you don't want is 3G to GPRS and back all the time - that is different frequency/tower/technology etc.
I have noticed - and suspect it the result of recent software updates being installed - mine goes to 3G when idle quite often, but switches to HSDPA when needed (data being transferred).
Short of advocating placing the warranty at risk by flashing the Huawei software - try/check some of the following:
Maybe just double check your PC for starters - what cpu/ram/os are you running?
Is USB2 alive and well on the machine?
Try using the longer cable and plug in both ends to ensure full power to the modem.
Check all possible power saving settings?
Windows XP - latest service pack (2) and no updates wating to be installed - I have noticed some XP machines becoming cr@ppy when these updates are downloaded and not installed.
If you modem is left plugged into the same PC, try Vodafone Mobile Connect - think they are giving v9.1 on a CD lately - guess I am not the only one who was bleating...
Happy hunting.
