I have been working with a "K" machine for a while, and I am getting a 24 volt low error, I have changed the heater rod, the power supply, the complete card cage assembly, motherboard etc. Everything that would drop or draw the voltage down, I think I have covered. Anybody with suggestions, please, I am all ears...

When is this occurring, on start up, or when you go into dialysis or a cleaning cycle? Have you tried plugging in the hydraulics from another machine temporarily to see if you can isolate this problem to the hydraulics or the the card cage? Plug the sensor board cable and the actuator cable into the hydraulics of another machine. Turn the heaters off with the switches on the power supplies. Maybe you have a sensor or actuator cable that has been damaged, so check that out also. Most of our machines have the CMS208K equipment on them, and the box which is mounted inside of the upper back cover was hitting the ground wire terminal ends on the ground tree, and that was pinning the actuator and blood pump ribbon wires and damaging them. We had about a dozen shorted out ribbon wires before we realized what was happening. Now when new machines come in we have the Fresenius tech that installs them move the ground tree back about an inch so that the terminal ends don't hit the box and the ribbon wires.

This is happening in any mode. I will say however that when unplugging the sensor board and acutator board cables it went away. I changed out the sensor board cable to see if this would make any difference, no change.

Try a test board.

Could be one of your motors (dear/flow), try disconnecting individually at the distribution board, then turn the machine on to see if the alarm goes away.

Hunter1, the heater rod is 120V, so that wouldn't cause the problem. I'm not familiar with the K's so let us know what fixed the problem.

I had reached a end when I called tech support and that is when they advised me to try to change the heater rod, that it would/could cause the problem. I have tried unplugging the dear/flow motor, changed out every board down to the mother board, power supply, actuator board and ribbon cable, sensor board and ribbon cable. Even exchanged the blood leak sensor, but continue to get the 24 volt low? Talking about a puzzle, keep throwing out the ideas "ya-ll". It helps...Much thanks...

So have you isolated it to the hydraulic drawer? If so, maybe it's the distribution board itself? Usually the problem that we see with the distribution board is no 24 volts for the deair or flow motor and that doesn't happen very often. But you might have some kind of shorted pin(s) or contact in the board.

It would seem that the hydraulics are the direction to go, but I haven't changed the ribbon cable from the power supply to the power logic board. Ktech do you think this would be a possible?

I had a 24 volt low on an H the other day that someone else started working on. The machine would start up and allow you to select a mode, rinse or dialysis, and as soon as you did it would give a 24 volt low. I disconnected the actuator and sensor cables from the distribution board and that got rid of the 24 volt low so I figured it was in the hydraulic drawer. BUT, it wasn't, it turned out to be the power supply. I see you tried a power supply already. That is why I am telling you to plug that hydraulic drawer into a known good machine, and if the good machine will run that hydraulic drawer start looking somewhere else. If you have a good spare power supply set it on the top of the problem machine and wire it in temporarily with the rainbow ribbon wire to the card cage and the power logic ribbon wire. Shut the heater switch off and don't connect it. Its a tight squeeze, but if you arrange the power supply and the card cage just right you can make the connections work. If I had started working on that machine myself, I would have tried a power logic board first, then an actuator. Next step would be to try a power supply. Since I don't have a spare K function board(too expensive! we send them out to H&S as needed for repair) I would have swapped in one from another machine with the original RAM chip last. I hesitate to mess with the function baords unless I have to. Last step would be to hook the hydraulics into a known good machine if all else has failed. Or reverse that, plug known good hydraulics into the problem machine. This usually works for me with 24 volt problems. I never did check the 24 volt output of the bad power supply, but I suspect it is weak. I probably should have done that at the small test board on the mother board. And when you go into a mode and everything powers up at the same time the power supply just couldn't put out enough. You really gotta isolate this to one of three bigger areas, the power supply, the card cage or the drawer. Good Luck, hope this helps!

This message has been edited. Last edited by: Ktech,

So have you found the problem yet? How about a pinched wire between the UF pump and the bulkhead?

Unplug your sensor and actuator cables one at a time and turn the machine on each time. If the alarm went away after you unplugged the sensor cable, plug the cable back in and start unplugging each plug on the dist. bd one at a time starting at the right and going to the acid and bicarb pump-be sure the machine is off while plugging and unplugging. Likewise if unplugging the actuator cable does it, start at the acid and bicarb pump and go right through all the valves. Just remember to turn it off each time you unplug something. Also if you suspect the heater,flip the switch on the back and turn it back on. This works about 90% of the time. Hope this helps.

Hey guys I think I have isolated down to the hydraulics, I looked at the grounding tree, there is nothing obvious to the eye. But, I will keep trying. Will keep you guys informed, if anything else sparks a possibility let me know, thanks...Ya-ll..

Have you troubleshot the valves?

I have had this problem before and this is what I found to be the problem.
Blood pressure module power board (-12v DC/DC Converter). On the mother board towards the front of the machine next to power logic board. Also I have had a level detector cuase a 24v low. Good Luck.