Replacing the Display in an AFG5101

This is how I replaced the dull and low contrast display with a semi compatible blue/white display. These could be purchased fairly cheap from several places like
AliExpress or eBay. The P/N is 1602 or 1602A. It is semi compatible because the data part is compatible but the contrast and backlight controls have to be modified.

The new display. It differs from the original in how contrast and backlight are controlled.

The new display is about 1.5mm higher than the original. The original spacers are 6 mm + a 0.5mm washer. I had several 5mm spaces so when using them
instead of the original spacers & washers the distance from the top of the display to the front panel would be the same.

The original backlight is controlled with a special module located on the front panel board and it is not compatible with the new display. In fact the backlight
LED in the new display could be destroyed by this module if connected to the same pads as the original which I found out the hard way. The original backlight
could be changed from the front panel but it didn't work very well so it's not a big loss to discard this module.

Although the schematic looks like the contrast could also be changed I have not found a way to do that in the original setup.
On the connector between the display and the front panel board there was a voltage divider network, not shown in the manual, between the contrast pin and
+5V which I removed and replaced with a common pin.

So I made a small circuit board with trim pots for contrast and backlight. It fits in the holes vacated when the module mentioned above was removed.

A: The holes from the original module where the new circuit board is connected.
B: The holes to which the backlight LED of the new display is connected.
C: Here is where the output of the contrast pot connected.
D: This run must be cut.
In addition the new circuit board is also conncted to +5V which is on pin 20 of P1 (bottom left) and to ground via several of the holes of A.
The pin count of P1 is from 1 to 10 going up from the bottom of the left row and then 11 to 20 going down on the right row rather than the conventional
way of count on a IDC connector which is odd numbers one one row and even numbers on the other row.

The new circuit board in place on the front panel board .....

with front panel intstalled .....

and finally with the frames installed and holes drilled for access to the pots from the outside.

The final look.

Schematics here

Email me with comments. /Håkan