I've now tried powering the SynScan with a car cigarette lighter port, which definitely ought to be sufficient amperage and voltage. Exact same behavior: once the azimuth motor starts, it won't stop.
I will ask the supplier for assistance, but am concerned as to whether they will offer it. Because there was an extreme shortage of FlexTube 250s in the UK during the pandemic, and as I wanted to give my son one for his birthday, I ordered from B&H Photo in New York, and paid the international shipping and import charges. I don't know if B&H can offer any remedy other than for me to ship the faulty base back to New York (!), or if SkyWatcher could help by offering repair at a UK-based facility (or even if they could, if they'd be willing to for a unit purchased from a US supplier).
If I don't have any good warranty options given the international nature of the purchase, are there SkyWatcher service centers in the UK that could repair the base for a fee?
Thanks very much,
-Brad