I've worked on several of the tb120's. The EMS system is a pain. But I will say I have never seen one of the ems boxes go bad. Every lift problem I've had has been because of a limit/safety sw. The TB 120 will not let you go above a certain height or extend the boom unless the axle is extended and the lock pin is reinserted in the hole. You can not fully extend the boom unless you raise it past a certain height. So there for, you can not come down unless the boom retracts. Usually it's automatically. If not, the EMS will squak and you boom in, then down. As stated, you operate within a very tight envelope of height vs extension. If it were me, I would be looking at the telescope limit sw, of which I think there are 2 and they are on the left side of boom, if you standing in the basket. They are mounted to a chessey bracket that is easily bent. Lil boxes, 2 inches top to bottom, 3 to 4 inches long, lil roller on end of arm. It may be sensing that the boom is too far extened and wont let you come down, but it will let you go up. Some had an EMS overide on the ground side controls just in case of emergency. These older 120's and such were old school man killers that were retrofitted with every safety sw known to man using the technology of the day! The new booms are soooo much easier.
