Zenith 25EC58 Restoration Thread

[Electronic M]

Originally Posted by vol.2

I just want to make sure you know not to scope the B+ unless your set is plugged into an isolation transformer, or you're using an entirely battery powered scope. You cannot scope anything in the set without isolating it or using a battery powered scope because the neutral line will short out to the ground lead on your scope probe because the neutral and the earth are connected at the circuit breaker.

I would, in general, recommend that an isolation transformer always be used for doing any live testing on a set, no matter how safe you think you're being, but I know not all people will do that.

Sorry if this is unneeded advice, but I just wanted to make sure that at least someone said this to you.

IIRC all Zenith CCIIs, besides the one flat chassis variant that had a switch mode module, had a big honking power transformer with full isolation so you don't need an outboard isolation transformer on these.
Although transformers can short between windings and keep working as though nothing is wrong (I had my outboard bench isolation transformer do this to me and ironically cause the very problem it existed to fix... I learned the hands on way) and it's wise to check chassis to scooe ground voltage with a DMM before hooking up a scope.