Playing with HDDL and a lot of 3409AT clunkers.

In all cases have used matching & working pcb and found the following.

A few clunkers re-calibrate with luck and give an opportunity to read SA.

Found that 04HS always is correct - 04 04 00 01 02 03 when the lucky clunker re-calibrates,
which leads to conclude that 04HS is not recorded incorrectly in SA
and the cause of the heads banging - the source is somewhere else ?.

When the clunker does not re-calibrate 04HS is read from RAM as 02 02 00 01

Any ideas ?

The clunkers which re-calibrate mostly show following :

01DM not read to RAM correctly or at all.
02PL and 1BPL vary
06DT in SA and RAM vary, but slightly.