HP-67 not working



#2

Hi,

My hp67 is stuck, displaying a fixed pattern and not responding to key presses.

Power cycling sometimes changes the pattern, but otherwise its stuck.

Using a digital oscilloscope I confirmed that main voltages (Vbat, Vss, Vgg are all OK: proper voltages without ripple).

Both clocks are fine as well.

SYNC looks OK (but has some ripple) as well as RCD.

However, STR is stuck high.

Should I assume that ROM0 (which generates STR) is broken and needs to be replaced, or should I be looking elsewhere?

Thanks

**vp

-----

Here is the SYNC signal:


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