Mini 40 Display Issue Restart


hamhog1
 

I decided to restart from the beginning in troubleshooting my Mini 40.  All I have is the top row of blocks.
Using the Troubleshooting guide, I did the following:
1.  Adjusted R36.
2.  Made sure IC2 was inserted correctly.
3.  Check to be sure no bent pins.  All were seated correctly.
4.  I heard the 20 mhz crystal at 20.005 mhz on shack receiver.  Also saw on scope.
Next I swapped the display board, IC2, and controllers with my Mini 20 which works well.  What I observed:
1.  Both mini 20 and mini 40 IC2s work in mini 20 but no backlight.  Neither IC2s seem to work in mini 40 but with backlight and top row. of blocks.
2.  Both display boards work in mini 20 but no backlight.  Both display boards show top row of blocks in mini 40 with backlight.
3.  Both controller boards work in mini 20 but no backlight.  Both controller boards show top row of blocks in mini 40 with backlight.
Conclusion:  IC2 in mini 40 appears to be okay.  Display board in mini 40 appears to work okay.  Controller board in mini 40 appears to be okay.
Next I measured voltages with my digital multimeter using the voltage sheet from the manual as a guide.
1.  All readings were nominal down to the reading for left side of C45.  Showed 1.28 v instead of 2.42 v. Also C46 showed .85 v instead of 2.30 v.
2.  I did not check ICs 5-10 at this time.
3.  LCD pin 6 showed .48 v instead of 0 v.
4.  LCD pins 7-11 all showed 4.94 v which is quite high.
5.  LCD pin 14 showed 4.94 v instead of 0 v.
6.  LCD pin 15 showed 3.71 v instead of 4.41 v.
Finally I checked continuity and resistance between LCD and IC2 with IC2 removed.  It showed 0.0 ohms resistance.

Trying not to get frustrated.  It probably is something simple, but where to look?

Thanks for any help.
Gary K4VIG

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