Reassemble.IT, Repair.IT – Eagnas Plus 8000 Electronic Tension Head

Last Saturday, I got a message that there was a Eagnas Plus 8000 Electronic Tension Head for me to look at. It was apparently new, but not working. I picked it up on Monday, after it had been returned by the customer.

This is a newer model of the Eagnas Plus 8000 that I had worked on previously – a white case instead of the older grey case. This one had been sold to a customer who said it wasn’t working, so the supplier sent a spare circuit board to the customer. Due to some problem with the assembly, it came back to the supplier – which is where I got involved.

The gripper assembly had been removed already – when I examined it, I noted that the microswitch wasn’t clicking when the white plastic actuating lever was pressed. I knew from previous experience that this would cause an error in the self test procedure that would stop the tension head from working.

I proceeded to remove the case and found that the internal circuit board had been removed from its supports, and cables had been removed from the board. Also I found that the drive chain for the carriage was disconnected. This tension head differs from the older one by using a different load cell, a much smaller one, which is connected in line with the drive chain. The older model used a much larger load cell (and probably more sensitive) which was indirectly coupled to the carriage.

Anyway, I had to reassemble everything before I could test it and work out what problem it had other than the suspect microswitch. This reassembly took some time, to remount the circuit board, and while attaching the cables, I found a couple of the contacts on one cable were a little loose – which was causing heating at the contact point. I removed the contacts and adjusted them so that there was better contact between the pins.

Next was to reconnect the chain. The bolt that had been used was a M4 bolt which was bent, and the end was stripped – looks like the nut had pulled loose. If that was the case, perhaps it had not been tightened properly in the factory. I replaced the bolt with a M4 bolt from my nuts and bolts collection, cut to the appropriate length and tightened up. The chain was then reattached which took some effort because it has a spring inside the joiner, but eventually it was done.

I then examined the microswitch which is mounted at an angle so that the plastic lever pushes the switch lever down, however – the switch lever was not bent to the correct angle, so when assembled, the switch was always activated. I bent the lever to an angle such that when assembled, the switch was not pressed. Then pushing down on the white plastic lever, I now heard the familiar click of a working microswitch.


Switch assembly

Here you can see the white plastic lever – and next to it, the silver microswitch lever. Pressing the white lever pushes down on the silver lever.

I then connected the switch cable and plugged in the power cable, and was glad to see that the self test shows three ticks.


Eagnas display panel

From experience, if the switch was pressed or not connected at power on, there will be a cross next to 3. Load-cell cable instead of a tick – which can be a red herring, since you need to know that the load-cell cable doesn’t just connect to the load cell, but also to the gripper microswitch. Most people don’t know this, and hence suspect that the circuit board might be the problem.

Once everything was back together, I set the tension to about 20 lbs, then put some string into the gripper with a digital luggage scale to pull and see if it stops pulling, which it did, but it wasn’t at 20 lbs, more like 14 lbs – which is probably ok. Why is this? Because the tension head is usually calibrated at the factory to suit tennis tensions at 50 or 55 lbs. If this tension head is going to used for badminton, then we would adjust the calibration to be more accurate at around 25 lbs. If the user has a digital luggage scale, they can also test it at various settings and end up with a calibration chart which shows what setting gives a particular tension.


Eagnas Plus 8000 Electronic Tension Head

Here is a final photo of the assembled tension head before I put it back into its box – looks quite nice, doesn’t it.

[Note] Other work done on this was to fix up the slide covers, that had been wrinkled a bit and to realign the slide cover guides to be parallel to the carriage movement. Not doing this causes the slide covers to jam.