have a Linkbelt 3400 quantum (late 90s model) with no power at the key switch. the machine was running fine until it shut off randomly while working and lost all power. checking with multi meter there is 24V going from wire at main battery cable terminal on the battery relay to the fuse panel. back of fuse panel shows 24V. However, all fuses are dead except the "shut down" fuse has 24v. all other fuses including key switch fuse have 0V. Batteries are good, I have replaced the battery relay (positive disconnect) during the process of trying to figure out the power to the key as the old relay was not functioning and was bypassed to make the machine run. The new relay is wired correctly as it matches the old one and the electrical diagram for the machine. I am working on checking all other connections and grounds. does any one have any ideas of things to check? Thanks i have attached pictures of the wiring diagram from the batteries to the key switch. WR 206 has 24V at the fuse box.
Does your machine have a thumb installed? The thumb controls won't be in the schematic. If you have one look for a diode in the circuit somewhere. We used to put them by the relay mounted behind the cab.
no thumb or aux hyd on this machine
You have three fusible links in the area of the master disconnect numbered 26 and 27. Those supply power to the fuse panel. A Q model is a pretty old machine even for me. Do you see any corrosion and can you unbolt the panel and tip it out to see the connections behind it?
The symptoms point to a break in the main power distribution bus at or inside the fuse panel. You have confirmed 24 V arriving at the fuse panel (WR 206 and the back of the panel), and the “shut down” fuse is live. Every other fuse—including the key-switch fuse—is dead (0 V). That pattern means the common feed that supplies the majority of the fuse positions is open, while a separate or upstream tap still powers the shutdown circuit. Most Likely Causes (in order) 1. Blown main / mega fuse or fusible link that feeds the main fuse bus Many of these late-90s Link-Belt Quantum machines have one or more high-amperage fuses or fusible links that supply the bulk of the panel. The shutdown circuit is often tapped before that protection, so it stays live when the main feed opens. 2. Failed or high-resistance connection inside the fuse panel Cracked bus bar, burnt terminal, loose stud, or corroded internal link between the incoming power stud and the main fuse rail. 3. Main power relay (if equipped) that is not closing Some versions use a relay to energize the main distribution bus. If that relay coil or contacts fail, you get exactly this split: limited always-hot circuits live, everything else dead. 4. Open or high-resistance in the heavy feed wire after the point where the shutdown circuit branches off. Recommended Checks • Visually and electrically inspect the entire fuse panel Remove the cover and look for burnt spots, melted plastic, loose nuts on the main power studs, or a separate large fuse/fusible link that is open. Meter from the known-good 24 V incoming point (WR 206) to the metal bus that should feed the dead fuses. You should see continuity / 24 V; if not, the break is right there. • Locate and test any mega-fuse or fusible-link holders near the battery relay, starter, or fuse panel. These are common failure points on these machines and often look like short heavy links or large blade/cartridge fuses. • Verify the new battery relay is fully closing and that both large terminals have solid 24 V with the relay energized. Also confirm the control side (small wires) is getting the correct signal and good ground. • Check all major grounds (battery negative to frame, engine block, and any ground studs near the fuse panel and key switch). A poor ground can produce confusing voltage readings, although your description sounds more like a missing positive feed. • Trace the key-switch power circuit from the fuse panel outward. Confirm the key-switch fuse position itself has no power on the supply side of the fuse. If the supply side is dead, the problem is upstream (bus/feed). If the supply side had power but the load side did not, the fuse would be blown—but you already noted the whole group is dead. Because the machine died while working and then lost all key power, the most probable single-point failures are the main feed fuse/link or an internal fuse-panel connection that opened under load/heat. If you can describe or note any large fuse, fusible link, or relay located near the fuse panel or battery relay (or post clearer photos of the back of the fuse panel and the main power studs), the exact component can be identified more precisely. In the meantime, start at the fuse panel bus—that is where the 24 V stops according to your measurements.