Hi Tina,
Not sure about repairing pH meters.
However, regarding testing pH of soil I can pass on a couple of techniques. Bunnings, or similar stores, often sell soil pH meters, with a long aluminium probe that you stick into soil, and a screen with a needle that gives you an analogue readout. Depending on what you are using it for, it's often sufficient. We use ours on excursions to the mangroves, where we can stick the probe in the lovely gloopy mud, and get a picture of the acidity of mangrove mud. In drier soils, weactually drive a tent peg into soil first, maybe drip some water into the hole, then put the probe in.
Another technique we've used with a fair amount of success is to lay one or two pieces of pH paper on the bottom of a beaker, cover them with circles of filter paper, then mix the soil sample with a little water and tip into the beaker. After a minute or so, dump the lot onto newspaper. That way the pH paper is not exposed directly to the dirt, but you can get a reasonable reading on the pH of the soil. Less chemicals etc than the old BaSO4 method.
Cheers, K
