Here is your parts breakdown
Model MDG5500AWW

Here is the tech sheet, service manual and troubleshooting chart
http://www.servicematters.com/m...ibrary/docs/16026750.pdf
http://www.servicematters.com/m...ibrary/docs/16023110.pdf
http://www.servicematters.com/m...ibrary/docs/63902110.pdf

Could not find a 8.8 error but 8 looks like it is a keyboard error.
Try to run the diagnostics, you may be able to narrow it down a little

Unplug the unit and open up the control console
Remove the ribbon cable from the control board
Looks like the ribbon cable has a connector on the end so clean the edge connector on the cable and the board with a tooth brush and some electronics cleaner (available at electronics supply stores) or isopropyl alcohol (available at drug stores).
Also check the ribbon cable for hairline cracks running across the tracks. A magnifying glass is useful here.
Be gentle and do not reinstall the cable till all the solvent has evaporated.

Give it a try, You may get lucky.

If no good, use a meter to check the keyboard switches.
You are trying to confirm that the keyboard is the problem since the most likely culprit is the keyboard but the control board could also do this.
You want to take the guessing out of ordering a part since most places will not allow the return of electronic components.