I think it is a MPU issues but I wanted to make sure what else I can try before I go out and buy a new board. Trident, when turned on, the speaker makes a loud continuous sound (medium pitched) and will not stop. All the lights turn on and do nothing else. Displays do not show anything I can see it has power.

This is the first STERN I am working on so this is new territory for me. Before I do anything else, wanted to get advise what to do next. Checked fuses and look fine. I do have a multi-meter, what/where should I check the voltages? There is battery corrosion on the MPU but the previous seller stated they had it working. Assuming that all the lights come one and it does play a sound, would indicate that the PS, rectifier and sound board are fine.... is that a safe assumption?

Is there a away to put the board is a diag/test mode?

Thank you all. I will work on this first. I will have time tomorrow to check this.

The MPU is crap. Tried swapping out the U chips and no results. Ordered another board. Now I need a SB-100... any ideas?