[Avid-L2] Deck or reference problem??

We have an older HDW-250 portable HDCAM deck that I've hooked up to our Avid (Adrenaline, running MCS5.5 on OSX) to do an occasional assemble edit with.

Half the time, I get a normal, clean edit. The other half of the time I get an edit point like the one attached: one frame of a detailed 'checkboard' pattern, with both outgoing and incoming pictures mixed. (Hope the attachment comes through.)

Material is HD, of course - 1080i for broadcast. Using an NTSC 59.94  synch generator for REF input, not tri-level. Also, the error log is showing entries like
V PLL Unlock
No SDI input
No PB Ref
No LTC Repro

Can anyone tell me if this is a synch problem, setting problem, or do I need to bite the bullet and send the thing out for servicing?

Any input appreciated!

Tim Selander
Tokyo, Japan