Help with PM2 Rev 2.1

gmiller · Post by **gmiller** » September 14th, 2020, 2:05 pm

Hi,

Recently started having issues with my PM2. For a bit it seemed like it almost needed to heat up and would work after 5-10 min of rowing, but now it doesn’t come on. It looks to be in good same with little to no corrosion. When I take it apart and and test a few connections with a multimeter it starts working again. After not using it for a few hours it won’t turn on again. Tough to troubleshoot without a wiring diagram.

Any ideas on how to get it working again would be appreciated. Hoping to avoid buying a PM5.

Carl Watts · Post by **Carl Watts** » September 15th, 2020, 2:48 am

Do a search on this forum is all be covered in the past.

gmiller · Post by **gmiller** » September 15th, 2020, 10:36 am

I’ve gone threw a bunch of the old posts. I see no obvious trace breaks or corrosion, so I tried some simple diagnostics. I’m no expert but handy enough.
1) I am getting 3v when measuring between the +3D via and battery negative, across the top battery leads, and across +3D and R46 (next to C1). I think my battery terminals and main power traces are fine.
2) On the MAX859 I'm seeing 3v between pin 6 (out) and pin 7 (gnd) and 1.25v between pin 2 and pin 6.
3) On the Max1044 I’m seeing 3v between pin 3 (gnd) and pin 8 (V+) and 1.48v between pin 3 (gnd) and pin 5 (Vout)
4) Top negative battery terminal to R46 is 0.3 ohms
5) 2.7v (seems alittle low) across large yellow tantallum capacitor below battery terminals and 3v across the one at the bottom by C17.
6) C10 to top negative battery terminal is 0v and C11 to top negative battery terminal is 3v. Could C10 be my issue?

https://imgur.com/a/y5ByHRS

Carl Watts · Post by **Carl Watts** » September 15th, 2020, 4:26 pm

1. I now replace C9 in the later versions of the PM2 because its the wrong capacitance. Earlier versions used a tant here and it should be 10uF and not the 1uF installed and then you will see the negative Voltage from the 1044 go from -2.77V to -2.99 or even -3.00V.

2: Check you have continuity between the lower 2 battery terminals as there should be a short circuit here.

3: You really need a decent milliammeter to diagnose the problem. The Rev 2.1 should use about 1.6mA to 1.7mA when turned on on like 0.050mA when in standby. Various other currents indicate different types of problems. How much current is it using on run and standby ?

With the 3V present at the output of the 859 and the two 3V present across the two yellow tantalums to the 1044 indicates the power supply is correct. The 1.25V is used as a reference and it also goes to the top of the board for the Op-Amps, however the screen should come on.It should still run with a DC supply to the PM2 as low as 1.3V and a "LO BAT" appears on the PM2 screen. With 1.28V to a 3.6V supply, the output from the 859 should stay close to 3V.

The most common fault on these is the 1044 fails. There should be -3V across C10 and +3V on C11.

gmiller · Post by **gmiller** » September 16th, 2020, 4:25 pm

Yes, continuity between the lower 2 battery terminals.

I measure 2.6mA running and 0.17mA in standby assuming I measured at the right spot.

Would this point to C10 being the problem or something else?

You really know a lot about these. Thanks for the help!

Carl Watts · Post by **Carl Watts** » September 16th, 2020, 5:31 pm

C10 will not be the problem.

Have you got the plus and minus 3V from the 1044 ? Put you meter across the two yellow tantalums C10 and C11 observing the polarity of the capacitors.

When the 1044 fails it drops the -3V output. The LCD display requires an AC supply of +3V and -3V and will not come on without both.

How much corrosion on the board ? if the board is totally clean then I put money on the 1044, just replace it they are a few dollars.

Current draw indicates the micro is working, it just cannot display anything.

gmiller · Post by **gmiller** » September 17th, 2020, 10:49 am

The -3v across C10 is not there. Board is very clean. I’ll try a new 1044 and test my soldering skills. Thanks for all the help. I really appreciate it.

Carl Watts · Post by **Carl Watts** » September 17th, 2020, 5:15 pm

You can just put solder down both sides of that 8 pin IC, whip the iron from one side to the next quickly and just flick it off the board.

Thats what make the PM2 such a great monitor, you can easily replace all the parts on the board. Try removing and soldering some of the later devices like the BGA micros and they are almost impossible even with expensive hot air gear.

RR · Post by RR » October 3rd, 2020, 9:44 am

Similar problem with a PM2.
Worked ok but then with cooler weather and room temperature would cut out and not restart.
Stripped it down, used a hairdryer to add some heat and try and remove moisture.
It worked
Kept an eye on it and it went nuts again after about 7hours of checking every 30mins.
Applied a bit of heat and i5 worked again!

Carl Watts · Post by **Carl Watts** » October 3rd, 2020, 8:34 pm

RR wrote: ↑
October 3rd, 2020, 9:44 am
Similar problem with a PM2.
Worked ok but then with cooler weather and room temperature would cut out and not restart.
Stripped it down, used a hairdryer to add some heat and try and remove moisture.
It worked
Kept an eye on it and it went nuts again after about 7hours of checking every 30mins.
Applied a bit of heat and i5 worked again!

The MAX1044 is faulty, The PM2 should still work even if you put it in the freezer for 30 minutes and take it out it should still turn on.

RR · Post by RR » October 7th, 2020, 11:58 am

Carl
Ok thanks for that. It is now working perfectly after being in the house since Sunday.
What does 1044 look like, I’m not very techy

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