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PM2 Rev 2.1 Display turns on but no reading, remains zero
Posted: July 16th, 2023, 4:29 pm
by tdixo
Hi all
Im currently in the process of repairing my PM2 rev 2.1
The battery tabs had corroded off so I soldered on some new ones.
The display turns on but remains on zero when rowing.
I haven't check the sensor, I'm not sure how to. The sensor wire has a resistance just over 100ohms
The MAX859 has two voltages which go through the two 100ohm resistors below the batteries.
The sensor cable plug is slightly corroded but the solders and solid.
Here is a photo of the pcb
https://imgur.com/a/DCZohUs
Any help to identify the cause of this issue would be greatly appreciated.
Thanks
Re: PM2 Rev 2.1 Display turns on but no reading, remains zero
Posted: July 16th, 2023, 5:43 pm
by Carl Watts
Make sure the 1.25V reference voltage from the MAX859 actually makes it to the top of the board along with the 3V as well.
The voltages end up at a chip ceramic C7 and the yellow Tant C15.
If the Voltages are present then chances are the Tach Op-Amp has failed, its the 7611 directly above the Heartrate socket.
Try a strong magnet on the sensor and if the monitor turns on but doesn't work on the rower, its probably the Op-Amp as the gain can crash. Its probably NOT the MAX922, only ever had one of those fail in over 10 years and what was a couple of weeks ago.
Check the yellow Tants C1 and C15 that can crack in half. Not sure how this happens, battery leakage either causes a reverse polarity, high Voltage or something that can kill them.
If the battery leakage is bad then the monitor is stuffed, Acid gets into that component array next to the heartrate socket and that Op-Amp will not work either.
In most cases now the monitor is scrap, I would probably just bin it and buy a new PM5. If its just a component that's has failed on an otherwise perfectly clean board, they are an easy fix, if the leakage is bad its not worth your time on a one off repair on something that's made in 1996.
Just checked your picture, that's pretty clean. U13 has probably failed. The sensor on these reads about 100 Ohms, its just a coil of wire.
Re: PM2 Rev 2.1 Display turns on but no reading, remains zero
Posted: July 17th, 2023, 7:59 am
by tdixo
Carl Watts wrote: ↑July 16th, 2023, 5:43 pm
Make sure the 1.25V reference voltage from the MAX859 actually makes it to the top of the board along with the 3V as well.
The voltages end up at a chip ceramic C7 and the yellow Tant C15.
If the Voltages are present then chances are the Tach Op-Amp has failed, its the 7611 directly above the Heartrate socket.
Try a strong magnet on the sensor and if the monitor turns on but doesn't work on the rower, its probably the Op-Amp as the gain can crash. Its probably NOT the MAX922, only ever had one of those fail in over 10 years and what was a couple of weeks ago.
Check the yellow Tants C1 and C15 that can crack in half. Not sure how this happens, battery leakage either causes a reverse polarity, high Voltage or something that can kill them.
If the battery leakage is bad then the monitor is stuffed, Acid gets into that component array next to the heartrate socket and that Op-Amp will not work either.
In most cases now the monitor is scrap, I would probably just bin it and buy a new PM5. If its just a component that's has failed on an otherwise perfectly clean board, they are an easy fix, if the leakage is bad its not worth your time on a one off repair on something that's made in 1996.
Just checked your picture, that's pretty clean. U13 has probably failed. The sensor on these reads about 100 Ohms, its just a coil of wire.
Hi Carl, thanks so much for your help.
Ye, the voltages at C7 and C15 are present. Will go ahead with trying the 7611.
Having a bit of trouble finding the original Harris chip online, do you know if either of these would work (I have a Farnell account)?
https://uk.farnell.com/analog-devices/i ... 02?st=7611
https://uk.farnell.com/renesas/icl7611d ... 66?st=7611
Thanks again
Re: PM2 Rev 2.1 Display turns on but no reading, remains zero
Posted: July 17th, 2023, 8:24 pm
by Carl Watts
You need the SOIC surface mount version.
https://uk.farnell.com/renesas/icl7611d ... 15?st=7611
TIP: Put solder down both sides of it and bridge all the pins. Then flick the iron from side to side melting all the solder enough and slide it off the board.
If changing it doesn't fix it, then you ideally need a scope to check the input to it and the output of it that then goes through the bottom of the MAX922 and onto the micro.
You should check the 3 magnets in the flywheel, they should each hold the weight of a paper clip.
Check the solder joints on the TACH socket connector for a dry joint.