PM2 not counting strokes.....suspect MAX 859 regulator

[TSUM]

I have a model C with PM2 that no longer counts.

I had the battery leakage issue but managed to restore all functionality for a short while. initially the count function worked, went intermittent and then stopped completely. The rest of the display functionality is fine. I assume the LCD is powered from the MAX 1044 which is working OK....apart from displaying counted strokes and time/meters etc.

The sensor wire measures 104 Ohms and the resistance changes up and down if I rotate the fan. With the fan removed I can trigger the PM2 to switch on by "flicking" a magnet very near to the sensor. I've checked the magnets in the fan, they are in good condition. I've ensured the fan bolt is tight.

I'm speculating that there is a sensitivity issue somewhere. I'm assuming the sensor and its wire is fine .......so the monitor counting circuity is suspect?
As the count function did work initally after repair perhaps there is poor connection somewhere?

Further investigation indicates an issue with the MAX 859 regulator. Based on the data sheet it should output 3Volts, it shows 2.6volts. Most of the other pin voltages are out of spec. If the 859 is not powering the op amp etc in the sensor pick up chain then this could explain the sensitivity issue?

I plan to replace the 859, but before I do, have others seen a similar problem?

Any suggestions of voltages or other things to check would be much appreciated.

thanks Tim

[Carl Watts]

If you change the supply Voltage to the PM2 from between 1.3V and 3.6V, the output of the 859 should remain at 3.0V.

I think you will find you have lost the earth connection to the 859. This results on the display coming on but the Voltage to the Op-Amp that in connected to the tach sensor will not work because it needs 3V and the ref Voltage from the 859 which is 1.25V.

The left hand side of the chip mono cap at the top of the board side of the 859 should be connected to the negative of the battery.

PM me if you need some help directly via e-mail.

[TSUM]

Hi Carl, thanks very much for your expert suggestions...very much appreciated. I'll get to work and be back to you. thanks Tim