Inspiron 1545 no display on laptop, external works fine

I know this topic has been discussed before but none seem to be the same as my situation.

I have a Dell Inspiron 1545.  When turned on I get nothing on my display.  Connecting to an external display works fine.  Here are the current steps I have taken without any results:

1.  Tried the memory swap thing....no display.

2.  Checked fuse on motherboard.  OK

3.  Installed new cable.  No change.

4  Installed 3 known good displays....same part number that was in laptop as original.

5. Installed 2 new good motherboards....no change.

6. This is an LED monitor  so no backlight or inverter.

7. Removed keyboard....pressed on all the "known" areas that people have mentioned on this forum.

Connect is to an external monitor and all is good.  Try the FN key an the F1 no change.....Sure could use some more ideas as I am completely out.

Thanks

Frank

10th SFG(A)