Erratic Force Curve

[HPL]

Some weeks ago in our club one of the PM3s started to show erratic force curves with spikes on various locations of the curve. Two examples here:

erraticNearFinish.jpeg (22.92 KiB) Viewed 4568 times

erraticNearCatch.jpeg (23.69 KiB) Viewed 4568 times

It happens about every second or third stroke. Also does the force curve disappear immediately at the end of the stroke. Normally it disappears at the beginning of the next stroke.
Except this, one of about 30 strokes the number of spm goes wild. While I constantly row 20 spm, PM3 shows something like 90 or even 14 spm. When this happens also the pace goes from a constant 2:04/500m to 1:45. Don't know what happens to the recorded average(s).
The erg is a model C made before 2003 with a PM3 retrofitted.
PM3's data:

• Firmware Version 108

• hardware version 433

• serial number 300033446

• date code 2572005

• lifetime meters 794646

Is this a known problem?

[Citroen]

1. Check the PM3 is configured for the right model
2. Check the flywheel sensor
3. Check the cable from the flywheel sensor to the PM3
4. Check/replace the PM3 batteries
5. Swap the PM3 to another ergo
6. Try the PM3 from another ergo on this one
7. Check the magnets are in place on the flywheel
8. Call Concept2 for support

[jamesg]

Had the same thing a year ago on a 2004 C: odd readings and spikes on the bar diagram. After much bolt tightening and similar, I replaced the sensor. Most oddities and spikes disappeared.

Recently I tried Rowit with a laptop. On battery only there were some extra spikes on the bar diagram. When I plugged in the laptop power supply there was a spike every other stroke.

So a possible guess, apart from a sensor or cable fault, is that the PM3 is sensitive to voltage spikes from wherever; as it must be, it's job is to count impulses. Maybe even the long sensor cable can act as an aerial. If C2 have altered the arrangements (screening?) on more recent machines and PMs, best follow them.

[HPL]

Today I swapped the PM3 to another Ergo and vice versa, result: Problem is caused by the erg.
I had a closer look at the cable and found it broken near the plug.
I will see if I can get a new plug and somehow fix the cable or if I will have to buy (and mount) a new sensor with cable.

Citroen, thanks for the checklist.

[Citroen]

Get a whole sensor/cable assembly it'll be a better outcome that way.

[HPL]

Mounted a new bought sensor/cable but still the same.