Repair.IT – Eagnas Plus 8000 Electronic Tension Head

A follow-up to my recent “Review.IT” article is in order. This is the one where the load-cell had a wire pulled off of it. After some inspection of the load cell – that is, after removing the silicone compound that covers much of the strain gauges, I could see that everything else was intact. If I wanted to do the repair, all I had to do is to connect the yellow wire and then put a blob of silicone sealant on it.

Sounds easy, doesn’t it – except that the pads are very small and the wire is very thin. I put it onto a holder that allows the load cell to be held by clips, then positioned a magnifying glass over the load cell. In this way, I could clearly see the pad that I was soldering to, and of course the yellow wire. This was done in due course – then the other three load-cell wires were connected. All joins were then covered in heat- shrink.

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Load cell connected finally!

The other tension head came in as expected – so using this one, I was able to determine the load-cell connections. On inspection, the white goes to green, black to red, yellow to yellow (which was still connected) and red to black. The photo above shows the heat-shrink in place, but not yet shrunk.

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New Eagnas Plus 8000 internals

Here is the load cell and connector mounted back into the tension head with the chain re-attached.

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load cell attached with chain

Here is a close-up of the mounted load cell – I had to replace both of the screws that hold it to the chain and the carriage because the old ones had been stripped – I think because the original screws were not strong enough – hopefully, these ones will last longer.

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The New Eagnas Plus 8000

Now a final photo of the completed unit attached to my test bench ready to have its calibration checked and adjusted if needed.

By the way, notice how the blue gripper assembly doesn’t yet have the gripper installed? The reason for this is that I had to modify the assembly because the fastening screws were bent, by going through a 6.4 degree bend – that is the slope of the assembly relative to the horizontal. The holes drilled and counterbored in the assembly were perpendicular to the assembly, but were not lined up with the vertical holes in the mounting.

I put the gripper assembly into my mill and adjusted it to have a 6.5 degree slope, then used a 10mm end-mill to do the counterbore. This was followed by a 6.5mm drill to ensure that there was a vertical hole going through the assembly at the right angle. After doing this, the mounting screws can now be tightened up properly without having to bend in the middle.

The next tension head to look at is the one that came in, apparently had been smoking – and the transformer looks like it has been cooked, with the varnish having boiled out of it.

Review.IT – Eagnas Plus 8000 Electronic Tension Head

Just a couple of weeks ago, after the repaired Eagnas Plus 8000 Electronic Tension Head had gone back to the client, another came in – this time it had been opened, with case screws removed and no gripper head. I took the case off and found this.

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Broken load cell

Obviously, one of the problems of having an inline load cell – that is, a load cell that is connected in line with the pulling force, in this case the chain – requires that the fasteners that connect the load cell should not come apart. In the previous tension head, the bolt that connected the chain to the load cell had come off – however, in this case, the bolt that connected the load cell to the carriage failed, which meant that the wires to the load cell, the yellow one – had been pulled off.

Usually, this means getting a new load cell as it might be difficult or near impossible to repair. Another thing is that getting an equivalent load cell could be difficult if the manufacturer is unwilling to provide spare parts – which is the case in this situation.

On the bright side, I realized that one of my digital luggage scales that I use to check the tension heads might use a similar load cell – and it seems to be the case.

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Digital luggage scale – cover removed

I opened my luggage scale and sure enough, the load cell is the same size – but is it similar enough? The wiring color is different, green, white, red & black instead of yellow, white, red & black. The notation on the circuit board indicates that green is +excitation, and black is -excitation, hence white is +signal, and finally red is -signal.

I found a site that showed some load cell wiring colors – Load Cell Wire Colors which shows that this is a common wiring arrangement, so that is good to confirm.

Now the broken load cell has yellow – probably instead of green. The load cell strain gauges are covered in a soft silicone sealant for protection, and I could scrape it off and have a look at the strain gauge and see if I could perhaps reconnect the yellow wire.

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Load cell

It looks like I can reconnect the yellow wire as it had broken off on the solder pad.  If I reconnect the yellow wire, I then need to work out where the other wires should go to – three wires to connect to three other wires – what could go wrong? Ok – the yellow wire is still connected to a yellow wire, so the other wires on the connector are red, black and green – so presumably, red to red, black to black and green to white would be an obvious first try.

Anyway, I don’t have to rush on this repair because the client came back to me saying that the other one I had repaired had started smoking and his customer no longer wants them both, so now I can wait until the other tension head comes back eventually and check the wiring colors. In the meantime, I might order a similar load cell from aliexpress.

[P.S. When the smoke leaves a machine, it generally stops working, until we can repair it to put the smoke back in.]