Gottlieb Sinbad (Gottlieb, 1978) loud buzzing

[minkole]

Still working on this thing as a newbie...
I noticed my the set of 4 drop targets didn't work. One of the wires to the coil was cut so I checked it with a multimeter and the coil was bad.
So today, I soldered a new coil and had a good reading. I was excited until I turned on the game and it starts with a really loud buzzing noise. I immediately turned it back off.

I have new CPU and display boards for the game but am hesitant to put them until I know what causing the new coil to do this. I don't want to mess those up.

Any ideas?

 

[pinballdaveh]

When coils go bad they take out their driver transistor on the driver board. Sometimes a bad driver transistor will be blown apart making it easy to spot. Did the new coil come with a diode already installed?

 

[minkole]

Yes, it has a diode on it.

Do you think when the original one went bad that it messed up the driver board and that's why they cut the wire to to coil?

I have a new driver board that I can install.

 

[pinballdaveh]

On some system 1 machines a under playfield transistor is used to drive coils that the driver board doesn't have enough coil driver transistors for, but Sinbad is not one of those machines. So all coils are driven off of the driver board, except for flippers and pop bumpers. Drop target and bank reset coils are protected by fuses, usually mounted by the coils they protect. Remove the 3 playfield fuses and check their values. Swap out boards with new boards, turn on machine, and install proper value fuses 1 at a time. Coil problems should be solved. There is a 4th under playfield fuse near the outhole kicker, that fuse protects the outhole kicker coil. If the the outhole stops working check that fuse.