07-09-2016, 09:28 AM
The Tektronix problem relates to solid tantalum beads used as supply rail decoupling. This mainly affects 500 power rack plugins, 7000 series oscilloscopes and their plugins. Tek, as we all did back then, used tant beads in this application, but with insufficient voltage overhead. So 6V parts on 5V rails and 16V parts on 15V rails - and that is why the voltage ratings are what they are.
The problem is when subjected to start-up transients - either voltage or current - in the fullness of time they randomly go short circuit. And they really are a hard short, either burning or causing other things to burn and/or the power supply to crowbar or go into protect mode.
The fix, as already suggested, is to replace them with aluminium electrolytics, with several times the capacitance to ensure ESR is comparable. In fact in later serial numbers, Tek did precisely that, perhaps because they had identified reliability issues with tant beads for rail decoupling.
I have not seen a failure in a tant bead used at other points in the circuits.
The problem is when subjected to start-up transients - either voltage or current - in the fullness of time they randomly go short circuit. And they really are a hard short, either burning or causing other things to burn and/or the power supply to crowbar or go into protect mode.
The fix, as already suggested, is to replace them with aluminium electrolytics, with several times the capacitance to ensure ESR is comparable. In fact in later serial numbers, Tek did precisely that, perhaps because they had identified reliability issues with tant beads for rail decoupling.
I have not seen a failure in a tant bead used at other points in the circuits.
