it does work - what was happening is that while most of the time a 3s guider exposure takes a total of 4.2s to take and read out, sometimes it takes 6, 7 or even 8 seconds. PHD2 has a timeout setting that disconnects the guide camera after it is non responsive for 5 seconds. that's the cause of the disconnect. this timeout can be increased and in fact the PHD2 authors told me to just set it to 60 or 120s, which effectively disables it. it's in the camera tab of the "brain" menu in PHD2. had an uneventful run last night which lasted 8+ hours.