Broken PM2 monitor

[rabinkin]

I have a CII Model C with a PM2 monitor which failed. The batteries leaked, and caused some PCB erosion (seems like a not-uncommon occurance) around the battery leads. It looks like R24 is eroded away, and a one of the traces from the battery leads is exposed and cut. Does anyone have a schematic for the PM2, or even a notional drawing of what the the power supply side looks like... I'd like to wirewrap solder in a repair.

Conversely, does anyone have a cheap PM2 for sale?

Thanks,

Dan

[schweinlew]

Hi Dan,

I have a PM2 with the same issue: battery corrosion fouled the circuit board. I, like you, would like to get my eyes on a schematic so I could trace and fix the problem(s).

I hope that there is a solution out there. If you find any helpful information, please post it here.

(I would hate to drop $160 on a PM3, when I could fix what I have and am happy with.)

Thanks,
Will

[rabinkin]

Will,

I was sent here by the folks at concept2, specifically they said that Carl Watts might have some info for us... Where are you Carl?

Thanks much,

Dan

[Carl Watts]

lots of posts on this already if you do a search on this Forum. A very good one with photo's

http://www.c2forum.com/viewtopic.php?f=10&t=11589

The are others.

http://www.c2forum.com/viewtopic.php?f=10&t=10903

So far I have managed to get 90% of failed PM2's going again. The corrosion can get so bad the MAX859 falls off the board and at this stage it's game over when the tracks start falling off and you need a new PM3 or PM4.

The MAX 859 is a dc-dc converter that provides a constant +3V output for a wide battery voltage of about 1.8 to 3.6V input.

The LT1044 or MAX 1044 is a charge pump that provides a negative 3V for the LCD using one of the big yellow Tant capacitors. Later versions like V2.3 do not have the 1044 as the switching function must be provided by the Micro.

You don't need a schematic, just a sound electronics background and some patience with a multimeter and good rework solder gear.

Essentially you are looking for open circuit tracks. The most common to go open is the one lower right that runs under the battery terminal.

[rabinkin]

Carl,

Thanks for the advice. I got the PM2 fixed. We'll see how long it stays fixed - I'm worried about the the remaining battery acid crystals somehow doing more damage - but it's working like a champ for now. I replaced one surface mount resistor, and soldered in about 5 wirewrap wires across traces that got eaten away. Because the board is only 2 layers, its pretty easy to track down which traces got disconnected.

Dan

[Carl Watts]

Put vinegar on the board over the crystals then wash with water.

The PM2 is easy to wok on compared to the PM3

[rabinkin]

Yeah, the PM2 is just 2 layers, and the spacing is still such that you can work on it with a soldering iron. I haven't done any soldering since grad school - 13 years ago now. It was a walk down memory lane. I imagine the PM2 board was designed in the early 90's - a pleasure to work on!

Dan

[schweinlew]

Dan,

Any luck on the soldering? I am afraid that my fine motor skills are not up to soldering on a PM2 board. Sad, sad.

Will

[1212sports]

I picked up a model c but the computer was not working. Same senerio where the battery leaked and even one of the battery contacts was completely gone. After some research I read a forum where a person used aluminum foil crumpled into a ball to create a contact area. I carefully cleaned the computer with bakingsoda and water. After letting it dry with the help of a hairdryer I used the foil and it has worked like new for weeks. Ultimately I would like to replace the contact but hey I'm too busy rowing now

Please note that this is not the right way to do this repair. I just don't want to be responsible if someone's computer gets fried or shorted out.

Hope this helps!