How do I test an electronic sensor ( on a rowing machine ) - NOW FIXED!

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Darkman
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How do I test an electronic sensor ( on a rowing machine ) - NOW FIXED!

Postby Darkman » 7 Feb 2020, 10:22am

Years and years back, I bought a rowing machine. It didn't get used and was in the garage for years. It's a Marcy RM413, from 2011.

We got it out a few weeks back and cleaned it up, all working, or so it seemed.

There is an LCD display on it, which connects to an internal sensor that sits by a rubber belt that pulls the flywheel. The display works, but it all stays at zero. The stroke counter, distance counter etc - nothing. It's getting no feedback from rowing at all. I've had it apart and there's basically a couple of wires going down to an internal sensor. I've cleaned all the electrical connections with switch cleaner, and the sensor itself with IPA but nothing's helped. Googling has turned up little information.

If I could source a replacement sensor it would be a five minute job to change it. So I emailed Marcy in the US, who told me to try their UK distributor Puretec Fitness.

They've basically said that they can't supply a new sensor as it's an "internal part" and something something something health and safety. :roll:

It's a bit annoying as it was a £200 machine and basically a [probably] £5 part is broken. Think they want me to just buy a whole new one. :?

Sooo.....

Does anybody here know how I might go about testing the sensor/wiring and getting this thing working? Anything else I haven't tried before I consign it to the nearest skip? Kinda don't want to do that as it works, but you've got no sense of progress/achievement with the computer not registering anything.

Ta!
Last edited by Darkman on 8 Feb 2020, 4:12pm, edited 2 times in total.

kwackers
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Re: How do I test an electronic sensor ( on a rowing machine )

Postby kwackers » 7 Feb 2020, 11:44am

You need to know what sort of sensor it is.

Could be a reed relay, or a hall effect device, or an inductor or optical or a simple mechanical switch.
Does it make physical contact? If not then you can discount the last.
The first three require a magnet to whizz past - can you see one? (Try waving a magnet at it see if anything happens).

A picture might help - particularly if you can see whatever it is that triggers the sensor.

backnotes
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Re: How do I test an electronic sensor ( on a rowing machine )

Postby backnotes » 7 Feb 2020, 1:42pm

At the risk of stating the obvious, have you tried replacing the batteries in the “computer” with fresh ones if the machine has been in storage? There might be enough juice to activate the display but not enough for the sensor to do its thing.

Then, it might worth checking that the leads that go from the sensor up to the computer are not either cut or shorted out, if you can get at both ends. A multimeter or similar would help with this.

If the sensor is a reed switch then a multimeter would also tell you if the switch is making a contact every revolution if you measure the resistance.

This manual https://www.manualslib.com/manual/98716 ... e=8#manual is for a related model, but suggests that you may be able to get at the wires to the sensor, and separately at the wires that come out of the computer part.

There’s a discussion here https://forum.arduino.cc/index.php?topic=598285.0 with a picture of the sensor and a magnet (but probably a completely different make of rowing machine) that may be helpful - the claim is you can tell if there is a simple reed switch or a Hall effect device depending on whether there are two or 3 wires going to the sensor.

Shame this guide https://firstdegreefitness.com/wp-conte ... -GUIDE.pdf isn’t for your machine, but the approach / advice / steps may help if the sensing mechanism is similar you yours.

In the past I have verified that a cycle computer driven with a reed switch operated by a magnet on the wheel is working by using a paper clip intermittently short out the two contacts on the back of the computer when it was removed from its bracket.

Good luck.

Darkman
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Re: How do I test an electronic sensor ( on a rowing machine )

Postby Darkman » 7 Feb 2020, 3:56pm

Hm, never thought to get a pic of the sensor as I wasn't planning on asking anyone for advice when I had it apart!

The batteries are rechargeable ones - charged them and put them in about two minutes before I noticed it wasn't working.

The sensor looks similar to the one in backnote's last link, except it has two "sticky-out-things" (excuse my technical terms) on it - one slightly shorter than the other. So is that two sensors built into one unit? There are two wires going to/from the computer so maybe it uses two sensors to calculate speed or something... I dunno. Anywho, when you pull on the pully-rowy thing, it pulls round a drive belt, which turns the fly wheel. It's this drive belt that the sensor is pointing at. The sensor doesn't touch the belt physically, so I guess I should be looking for a magnet. I can't say that I saw any - am assuming it/they should be attached to the rubber belt. Saying that, I didn't know I was meant to be looking for magnets as I have no clue how these things work.

On the other hand, if there's meant to be a magnet, and it's fallen off, it'd perfectly explain why nothing's working.

Think I need another go with my screwdrivers and look for/test with magnets. It's a pig of a job as there's about eleventy bazillion screws holding it together so gonna be a job for the weekend.

Thanks all!

rjb
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Re: How do I test an electronic sensor ( on a rowing machine )

Postby rjb » 7 Feb 2020, 5:25pm

If you cant get it going you could fit a cycle computer. attach the magnet to the flywheel and position the sensor as you would on a bike. It may require a bit of maths calculation to get the wheel size to approximate what you are trying to measure. Ive used one on a wind turbine to measure the revs per minute. :D
this link may be useful if going down this route.
http://www.reuk.co.uk/wordpress/wind/us ... rbine-rpm/ :wink:
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backnotes
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Re: How do I test an electronic sensor ( on a rowing machine )

Postby backnotes » 7 Feb 2020, 6:19pm

If you open it up again, then waving a loose magnet (e.g. off a bike with a cycle computer) near the sensor and seeing if the display wakes up might show if it is working / sensing a passing magnet.

I'd have thought a magnet would be on the flywheel rather than somehow attached to a drive belt, but I know nothing of rowing machines.

On a bike, the cause of a cycle computer not working often turned out to be that the sensor on the fork had just got bashed slightly and was no longer lined up with and close enough to the passing magnet, and simply needed twisting back. So that might be worth checking.

Darkman
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Re: How do I test an electronic sensor ( on a rowing machine )

Postby Darkman » 7 Feb 2020, 7:17pm

Well, couldn't wait til the weekend. It's not my style. :lol:

Took it all apart again, and sure enough, there are three suspicious-looking recesses on the side of the pulley, by the sensor. But all are empty. :?

So I had a rummage around, and found, stuck to the underside of the chassis out of sight, two small round magnets! Whatever they were held in place with has perished and they've just fallen off the plastic pulley.

But only two? Not three?? Turns out that it looks like only two of the holes have ever had anything in them as I can see residue from the glue in them, but the other one is squeaky clean. So, stuck the magnets in with double sided tape for now, and everything has sprung to life. All working perfectly.

20200207_183939.jpg


I do need to get some of that super-strong glue at some point and fix them in properly, but at least now it's working and I know that neither the sensor or the computer are faulty.

Massive thanks for all the info. Really appreciated and it's saved me a few quid as I was all set to buy a replacement machine this morning.

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NATURAL ANKLING
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Re: How do I test an electronic sensor ( on a rowing machine ) - NOW FIXED!

Postby NATURAL ANKLING » 10 Feb 2020, 11:55am

Hi,
Silicone rubber in a tube or evostick.
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philvantwo
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Re: How do I test an electronic sensor ( on a rowing machine ) - NOW FIXED!

Postby philvantwo » 10 Feb 2020, 10:12pm

Silicon is not an adhesive.
I'd use 'Sticks like sh*t' I've stuck loads of things with it and it's never let me down.
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NATURAL ANKLING
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Re: How do I test an electronic sensor ( on a rowing machine ) - NOW FIXED!

Postby NATURAL ANKLING » 10 Feb 2020, 10:20pm

Hi,
philvantwo wrote:Silicon is not an adhesive.
I'd use 'Sticks like sh*t' I've stuck loads of things with it and it's never let me down.

Liquid silicone rubber RTV.............Silastic etc.
I was thinking super glue but the adhesive needs not to set hard due to vibration, although super glue might well do the job?
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philvantwo
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Re: How do I test an electronic sensor ( on a rowing machine ) - NOW FIXED!

Postby philvantwo » 11 Feb 2020, 7:27am

Super glue dries hard and becomes brittle, I've always used 'Mitre mate' apply the glue to one part, spray the activator on the other, hold together for 10 seconds and its bonded. Used it 1000's of times on MDF mitres!
Sticks like shi*t remains flexible and it's never let me down once.
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NATURAL ANKLING
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Re: How do I test an electronic sensor ( on a rowing machine ) - NOW FIXED!

Postby NATURAL ANKLING » 11 Feb 2020, 10:27am

Hi,
Your evidence is anecdotal.
We all know superglue is brittle, but in some instances it is the only thing that will glue something really well, like rubber.
Like I said vibration might kill that sort of thing so I would go for a more flexible with strength.

of course it does depend on the substances you are trying to stick together, not all plastics glue well with superglue.
Something like silicon rubber wrist straps for watches I have not found a adhesive that works well with them?
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