Yamaha DX7 blocks on display only

Synth Repair
1

I am having trouble pinpointing the problem with my DX7 lcd display.

-It only displays blocks. So, i know its getting power.

-replaced display, but new one has same blocks.

-the synth sounds great.

  • After replacing battery I can load songs from a cartridge no problem.

  • it plays from cartridge

-All the connectors are secure and pass continuity between components.

  • data slider works. i can operate the programming partially but i cant really see what values im changing. I successfully manipulated pitch wheel and mod wheel values.

-LED works fine. No weird characters.

-Tried the mini potentiometer near wiring connector, but only changes brightness.

I did as much research as i think i can, even looking for a seller of the 9.426 mhz crystal. I don’t think it’s that because it sounds and the LED isn’t scrambled

I could just use it with patches and navigate the features blindly, but i bought it to program.

Can it be a bad capacitor? Or something more complicated?

I only paid $100 for it plus the price of the battery and display. That brings it to $150 total.

2

If everything else seems to work, we can therefore exclude the processor,
if you have already changed the screen and checked the connector,
all that remains is the circuit that drives the LCD, the PPI 8255 (IC12) :

LCD DX7
LCD DX72115Ă—996 257 KB

It should cost less than $10 !

3

I will give that a try. Thank you Didier.
The listing I found for the part says “programable”. Do I need to program it?

4

The 8255 is programmable in the sense that it can be configured in various ways ; it is the processor that will drive it.
So no programming.
If you change it, insert an IC socket.

5

Thank you!
The chip is on its way!
I’ll update after I install it.

6

Didier,
I finally got around to installing the chip. IT WORKS!
I also installed the socket like you suggested.
Thank you, I am so happy this did not become a parts synth.
Cheers!

1 Like
7

Glad for you !
Good job !