HP15C displays gibberish. Is it broken?

[GreyUser]

No clock in a voyager results in blank display. Every time.

No clock: An open rc network is the most common cause due to battery corrosion. I’ve never seen it occur on an early flex circuit model in the black diaper, only on the rigid pc board models. It’s tough to diagnose because the failed trace is on the hidden side of the pc board. Easy to measure though if you have Tony Duell’s schematic and you figure out where to probe with an ohmmeter. Easy to fix with a bodge wire on the component side once you confirm an open trace.

The display pattern shown on the failed unit of the OP is a processor/r2d2 comms failure, any number of causes. If a reset doesn’t fix it, it’s most likely a bad r2d2.

It is not bad LCD contact. Due to the way the display is multiplexed, regardless of the differences between the original 3:1 and the later 4:1 mux schemes, you could never create that exact display with a loss of connections, it’s physically impossible as the missing segments are common with segments that are in fact displayed.