The design of the MicroMag 2900 AGM has a few shortcomings. One of them is the linear z-slide mechanism that the instrument came initially equipped with. It is a Velmex Manual UniSlide (Model # SPA2509DM-S2.5, see picture) with Rapid Advance, scale, and Vernier. The slide features a limited fine adjustment by means of a clamping-like drive that can be engaged/disengaged by operating a lever (B). When engaged the slide is clamped onto the center rod (C) which can be fine adjusted by operating knob A. The fine adjustment has no end travel stop other than the end plate D, which on out instrument got regularly bent, as shown in the picture.
Also, the locking/clamping mechanism experiences mechanical fatigue after years of use. This leads to failure and ultimately to a sudden vertical drop of the slide and the attached transducer/probe, after which the probe detaches from the transducer and usually breaks.
To overcome the described problems I replaced this slide with another model from the same manufacturer. The new slide has the same specs as the old model, but has an unlimited fine adjust feature. The plain center rod is replaced by a threaded rod unto which the slide is attached to via a locking mechanism operated by the lever B. The center rod will now remain stationary vertically which fine adjusting, solving the problem of the bent end plate. Also, the mechanical fatigue will be highly reduced due to the presence of the threads, which provide vertical support. The model # for this new slide is A2509HM-S2.5 and it fits perfectly, with no need of modifications.