Yamaha DX7 – Installing Backlit HT44780 Display

My banged up Yamaha DX7 needed a new display as it was a bit dim and I also wanted a backlight I did not want to pay €20+ for a new display kit. In this video I show how I did this.

Before
After

Perhaps this would have been easier to just buy a kit but I did some searching and found out that it was possible to mount use any HT44780 (a display controller chip) compatible display and these cost around €4-6 on eBay. So I ordered the cheapest one I could find with a backlight.

The new display – Front
The new display – Back

While waiting for the display I discovered by accident that my display actually had a backlight, but it was very dim (the room has to be pitch black). Someone had at some point replaced the original display with one with an EL backlight which obviously had gone bad over the years.

The old display – Front (the black block is the EL driver)

The new display was obviously smaller than the one used previously. The mounting holes do not match the original ones.

The new display & the old one

When I looked in the service manual it seems as if the pin numbering was reversed. The display that had been mounted in my DX7 had the same pin numbering as my new one. So I am not sure if this is a mistake in the manual or if I am stupid

Pin numbering in the service manual – Reversed if compared to my new display

The new display has 16 pins instead of the original 14 pins. Pin 15 and 16 are used to power the backlight. This display had a built in current limiting resistor (R8 – 150ohm, see photo at the top).

If you are going to do this please check if your display has a resistor connected to the anode (pin 15), if not you must add one or you can destroy the display. I actually added one later on to reduce the intensity of the backlight as it was too bright when the room was dark.

Jumper wires for power to the backlight
Added an extra resistor later on

I had to improvise a bit to make it fit in the metal bracket before mounting it as the screw holes will not fit. I used one of the screws, twisted a piece of single strand wire and used some nylon spacers so the display could rest on something

New display mounted – Front
New display mounted – Side
New display with the plastic mounted

When the display has been installed you probably have to adjust the contrast to see anything. This can be done using VR1 on the main board

VR1 to adjust the contrast

Various images

The old display mounted in the case
The new display mounted
The old display with the plastic front mounted

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