Chuck wrote:

I wouldn't expect physical trauma to be the issue, more something
like a metal flash due to an arc, or tin whiskers... Something
like that.

The damage to the resistors in the unit was almost certainly caused by an electrical overload (the "trauma" to which I referred). Or, more likely, to a number of overloads perpetrated by one or more clueless previous owners on more than one occasion.

The other damage (disconnected wires, etc.) was caused by someone hamhandedly attempting to diagnose or repair the original overload damage, or contemplating harvesting parts from a unit they knew was damaged beyond any practical repair.

The only cure is to replace all damaged resistors with new resistors of equal or better quality. If they are in the oil bath, the complexity of any repair is raised exponentially. Note that there are almost certainly other damaged resistors in addition to the ones that the OP has identified.

As a practical matter, an instrument with damaged (overloaded) resistors will never work properly again. The only 720As I have ever seen that worked properly after damage of this sort were repaired by Fluke at astronomical cost.

Best regards,


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