PM2 monitor problem

[matt_sargent@yahoo.com]

My PM2 Monitor is going on the fritz and hoping someone can help me out. I have replaced batteries, cleaned contact points and LCD (with alcohol), etc. The problem is that the numbers display either very faintly or not at all. What's really weird about this issue is that if I row for about 20 minutes, the numbers all of a sudden reappear. Its like the monitor needs to "warm up" or something. Anyone hae any thoughts as to what this could be and if there is a good way to fix it?

[Carl Watts]

It's probably related to the LT1044 or MAX1044 IC that controls the LCD contrast by generating a +3V and -3V supply.

It's an off the shelf IC but you would need some repair skills or know someone with an electronics background to replace it as it's a surface mount device.

If there is any sign that the batteries have leaked in the past, ie any white or white & Green deposits on the board it will also cause problems.

[brianm8]

I have the same problem - a PM2 with extremely dim display (only visible under bright light, at an angle). I measured 3.03V between GND and V+ (input voltage?), and 0.39V between GND and VOUT pins on MAX1044 chip. Does it sound like this is causing the issue? Could you elaborate on how it is supposed to work?

[Carl Watts]

There are two small yellow rectangular tantalum capacitors labeled C10 & C11to the left of the 1044 which have the +3 and -3V on them with respect to the top left negative (-) battery terminal. The 1044 creates a -3V supply as it is being used as a negative Voltage convertor.

http://cds.linear.com/docs/Datasheet/lt1044.pdf

Look for any corrosion on the board as 90% of this time this has caused the problem with tracks going open circuit rather than a component failure.

PM me if you need more information.

[mccleanbavx]

Hi Carl,
I have a PM2 revision 1.7 I also have a screen problem, the screen will only turn off after installing the battery 5 -6 times then finally will light up, when it does the sensor will not read at all. i got a new sensor , but still not working , any ideas, i have looked for the max chip on this board but cannot find it

many thanks for ur help

Bryan

[brianm8]

Exactly what I was looking for, thank you!
I discovered that there is no -3V signal where there should be. I built a temporary -3V DC power source and connected it across the appropriate pins on the chip, and the PM2 has been working perfectly. Haven't yet decided if it is the chip or an open circuit (there is some corrosion and a few ugly solder traces on the board), will continue looking for a more permanent solution.

[2tx]

Nice post,
I know this is an old post, but I have a simular problem.

MAX1044 IC don't seems to get any power when pushing on button.
Have to row to get any power on the chip...

Dark display
No battrey corusion on the bord

C10 is missing the -3 volt