This is my first time trying to repair anything like this
When powering on, the display lights up fully, then shuts off. Nothing I do illuminates anything on the display after that. Voltage setting is correct on the back of the device.
I hooked up my oscilloscope to the serial interface where the power supply's top board should be communicating to the display, and I don't see any activity. The clock goes from 0 to 5V and stays there, and so do the DI and DO lines. So, unless I'm wrong, the board isn't even trying to communicate to the display.
The power supply also doesn't beep. According to the manual it's supposed to beep twice if the display communication fails, but it acts exactly the same whether or not I even have the display cable plugged in.
As a test, I kept the reset pin of U17 high while powering on. This time the power supply made a single beep. So the speaker works.
I checked the bias supply voltages as indicated in table 5-1 on page 99 of the service manual and they were within spec.
I checked the crystal for U17 and it appears fine. I checked U16's counter output, which is functional.
I'm not sure what else to test since the problem seems to be it's not even trying to communicate to the display at all.
Here's a link to the service manual & schematics
http://www.evernote.com/l/AIYJimveyXtBlrgRLf5X79Jrqq5ZUT4cgXY/Thanks for any help!