Great stuff retiredcaps, here we go...
A1) I'm not looking to get Fluke involved here. That would defeat the purpose. I want us to solve this one.
A2) You are correct about the schematics - I already had a look and can't find any.
A3) Pics are already available - see connected thread on 1503 to 1507 conversion below. But I will take some for identifying the main IC.
A4) I measured a 5vdc source (Agilent E3614A) using sw position 1 (set to dc volts). The unit turned off after 10 minutes and would not come out of this mode by any key press or dial position change. I removed batteries for 30 seconds to restart.
A5) I Measured a 100 ohm resistor using switch position 2 (set to ohms) and used the lock feature to maintain a continuous reading, otherwise I would have had to keep my finger on the Test button. This time the unit did not turn off. Perhaps using the lock test mode prevents unit from sleeping. The second attempt I pressed the Test button for a few seconds until the reading stabilized then released it to hold the reading. Ater 10 minutes unit went to sleep.
A6) Unit turns on and displays the VDC mode.
A7) current draw in "on mode" is 6.5 mA. Current draw in sleep/off mode is essentially zero or so small it is beyond my ability to measure, probably in the micro amp range. I don't have one of Dave's Micro Current meter add ons, I probably should have one.
A8) I Measured a 5.00 vdc source using sw position 1 (set to dc volts). The unit was powered by an Agilent 6612C system dc power supply set to 6.00 vdc. The unit measured the 5.00 vdc supply correctly in the Volt switch position and the current draw was 6.7 mA.
The unit measured the 5.00 vdc supply as 3.9 volts in the off position. Then 2 seconds later a strange thing happened. All segments started flashing rapidly for a bout 10 seconds then the display dimmed and finally turned off. Current slowly went to zero. Quickly cycling the unit from OFF to Volts (first two switch positions) yielded normal behavior. Occasionally all segments would display before powering down the display completely. I hate it when this happens. I needed to find a cause for the problem I was having, not fix the tester. Perhaps someone can shed light on something I am missing or not understanding.
A9) The main IC is a Texas Instruments M430F427 as seen in the photo below.
A10) The current draw in both volts and ohms mode when the auto power off occurs is zero or darn close to it as measured with my Agilent 6612C.
After the 10 min of inactivity, the unit powers down as before, but this time after a range change or button press it takes about 10 seconds for the unit to again turn on. That's strange that it won't do this immediately.
Thanks to retiredcaps for the troubleshooting layout questions - i'm learning more and more as I do this. Having a strategy is 99.9% of solving a problem.
I have a working meter but I really don't know why...