HP-67 not working
Message #1 Posted by Vassilis Prevelakis on 24 Feb 2012, 7:51 p.m.
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
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Here is the SYNC signal:
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