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HP-71B Startup Time - ROM Differences
09-10-2014, 08:59 AM
Post: #14
RE: HP-71B Startup Time - ROM Differences
(09-10-2014 03:54 AM)rprosperi Wrote:  Tonite, I'm just trying the alternate command sequence, ending with DISPLAY IS *. Will let you excited fans know what happens.

Interesting subject, Bob!
I do not own a 71B (it is on my wanted list to be acquired when funds allow it... Smile ) but I would like to know what was the cause of that long awakening time from a deep sleep symptom as well.

If all the planned operation procedures fails, maybe this issue can be caused by a small component (like a capacitor) failure inside the calculator PCB.

I have found out the service manual available for free here.
I did a search in that page for "71b" and found it. Very comprehensive documentation I would say.

From the service manual, page 2-10:
Capacitors C1, C2 and C8 (...) provides power supply noise isolation (...).
The symptom you describe fits a hardware failure in a resistor (higher value than the correct one) or most likely a faulty capacitor (lost capacitor and/or leakage).
- I would start by checking capacitors and the resistors in the neighborhood.
In fact I would just replace all the electrolytic caps with new ones.

On page 2-18 the deep sleep state is described:
On every 4 hours the display/timer awakes the cpu to let it service the real time clock.
The average current consumption is 20uA.
Other things to check:
- Remove all the devices (as previously recommended by Dave) to make sure there are no interrupts being generated from them (if one interrupt in being served, no other interrupts will be served until the current interrupt service routine returns, and that can affect the ON sequence - pls read page 2-8);
- Is the rtc updated after that long hours in deed sleep state?
- Using a good current meter (a digital multimeter should do it) check the actual current drain.

And section 4 - troubleshooting and testing - provides a very comprehensive checking procedures, like diagnostic recommendations, and hardware procedures to check all the components in order to eliminate possible issues - providing one's have access to the required tools like an oscilloscope to start with...

Good luck with the problem "hunting" and please keep posting additional information.

Jose Mesquita member

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RE: HP-71B Startup Time - ROM Differences - jebem - 09-10-2014 08:59 AM

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