NEED HELP Arrow 750 2100 Controls Air Pressure Switch Problems

[Industrial Tool]

Hello to all. I am trying to figure out what is happening with my Arrow 750. When I power up, the display shows the NCA Air Pressure Alarm for switch PS_AIR_SYS(I00:00/01). I have temporarialy jumped the 4 air pressure switches on the back off with no luck. Also, this machine has the DropsA oil lube unit installed. The LED lights that show pump healthy etc. do not light up. Any ideas on what could be causing these problems?? Any advice will be greatly appreciated.

[maver1ck]

That alarm sounds like the primary air pressure switch (see pic), not one of the switches that is part of the Dropsa unit.

Just follow your main air line into the machine, and there will be a pressure swtich as part of the regulator assembly.

[Industrial Tool]

The main air supply pressure switch was the first to get jumped. Even with it, and the others jumped, the NCA Air Pressure alarm still pops up.

[maver1ck]

Sorry, I misread your post to say you only did the switches on the Dropsa unit.

The alarm means the control is not seeing the 24V signal from the pressure switch, so I'd start with figuring out where in this chain you are losing the voltage.

There's not much in this circuit, start by checking to make sure you have +24VDC at the switch. If not, check for voltage on 424A. If this is +24, then check wire 1002-1 (pin 1 on the R1/P1 plug if your prints are the same as mine).

If you don't have +24 on 424A, you probably have a short somewhere bringing your whole 24V circuit to 0. If this is the case, start going through your prints and determining what else is drawing power on 424A. Disconnect these items individually to determine where the short is.

If you have voltage at the switch, check if it is being lost on 1002-2 (pin 2 of the R1/P1), etc, until you find where it is dropping out.

[maver1ck]

Originally Posted by maver1ck If you don't have +24 on 424A, you probably have a short somewhere bringing your whole 24V circuit to 0. If this is the case, start going through your prints and determining what else is drawing power on 424A. Disconnect these items individually to determine where the short is.

I jumped to this a little to quickly because I've seen 24V shorted in these machines a few times. If you don't have voltage on 424A, check the obvious things first, fuse, power supply, etc....before you start chasing down non-existent shorts.

And, once I thought about it I was getting a different alarm in those previous cases. If you have a short on the 24V, you shouldn't be able to power-up control up since the machine uses +24 to pull in TR1 for control power.

[Industrial Tool]

I replaced the 24V Power Supply within the last month. I checked the +24V on 1002 at the pressure switch, nothing. I ohmed out the 1002 wiring and showed continuity. Went to the Input Board, nothing at the board on 1002. Checked the new PS, it has 23.8V. Went to 424A at F9, 23.8V. Went to CB1, 23.7V. Followed 424A to the Input Board, 23.7V at TB3-1. I looked at the circut on the board and didnt see any breaks in this feed.

[maver1ck]

Assuming your machine uses the same prints as mine, if you have power on 424A at TB3_1, but don't have it on P1/R1, my next guess would be something on the input board.

It looks like you should should be able to remove 424A from TB3_1 and remove plug 1. If you check TB3_1 to pin 1 on R1 what do you see. If there's nothing there, either a bad connection to pin 1, or internal break on the circuit board.

Start by thoroughly checking the wires/connectors on P1/R1 to ensure you have good contact. I have seen some of these boards burn out the circuit path on the backside (although I think that was always on the 110V), so if you haven't pulled the board and checked the back side, it wouldn't hurt to verify no damage.

You could try bypassing the input board and bring +24 to directly to the pressure switch and see if this eliminates the alarm.

[Industrial Tool]

Well after a week with the flu, I'm finally back again. Removed the Input Board and there was a blown lead on the back. Already have a replacement in the machine, but now when I flip the main breaker in the back it wont power up. The drives at the bottom of the panel all start up but mothing else. I checked all of the fuses again and all were good. Also checked the powersuplies and they were good as well. Anyone else have this problem??

[maver1ck]

When you say "it won't power up" I'm assuming you mean the control doesn't come on. If so, I believe the relay to pull in the 110V is 24V coming through the I/O board you just replaced.

Since you indicated you have already checked the 24V power supply, since the board was just replaced, I would start by double checking all connections and wires to this board to make sure they are all seated well and where they are supposed to be.

If everything looks good, check at the green power button on the OSA to see if the power is making it there. This will at least let you know which side of the power button the problem is on.

[Industrial Tool]

It's more than just the control that wont power up. The red LED's on the communication board wont light up as they normally do. As a test I replaced the 110V Power supply that is next to the 24V Power supply from a working machine. Still nothing. I removed the new board to inspect it again and all leads look good. I checked each of the connections at the bottom of the as I re-installed them. All seated with no problems. All of the plugs are seated nicely to the new board as well.

[Industrial Tool]

Ok new news. I checked the new 24V Power Supply, only 1.2V to earth rail. Completely inspected every inch of 405 to fuse and 424 to all components, no frays or burns.

I unhooked everything from 424, checked power supply 23.8V. Started hooking up components one at a time and checking voltage.

Everything checked good until I hooked up the "new" input board (part# 1269581 rev E Serial 1070). Voltage dropped to 1.2V. With the input board out of the circuit I show 23.8V at all connections.

Luckily I had taken pictures of the old board for reference and all wires/plugs are in the correct places. Before installation of the "new" board, I placed it beside the old one and carefully inspected/compared the two. They were identical, except for the blown lead on the back of the old one.

Any ideas on what could drop the voltage from 23.8V to 1.2V when the input board is hooked up?

[Industrial Tool]

The connection in question is wire 424 to TB1-1 on the Input Board. I looked at both sides of the board to see where the circuit goes and didn't see anything coming out of the rail. What all does TB1-1 feed 24V to on this board?