Hey there,

No easy way in. You have to learn how to get under the playfield, locate the faulty target, unsolder it and resolder it (if fixed targets on the right, for a drop target see below).

For the drop targets (left ones), what you describe clearly shows that the whole bank should be taken out and cleaned. That should solve your issue.

From pics I saw (don’lt own a haunted house unfortunately), you only need to remove the upper playfield to have access to all targets.

https://www.ipdb.org/showpic.pl?id=1133&picno=40161