I haven't followed this thread for a day or so due travelling after a holiday
Just to clarify, I spotted on the 7020i manual there were two 120 primarys (one with a tap for 110), so that would say there should be 5 wires coming from the primary side
If there's six then it could be an undocumented thermal fuse connection that's now blown and O/C, but I couldn't quite see that from the photo's (which have now disappeared anyway?!)
If there are indeed six wires from the primary then I suggest emulating the blown thermal fuse by bridging at the pcb to regain the ~16ohms total primary impedance. The amp (if no faults) should now power up for you to check AC secondarys
I'm not suggesting return to customer in this state , but it would give you opportunity to get the secondary voltages (and currents if you break each winding in turn to measure current)
As for working out the secondarys without the TX working , one could simply work back from the DC levels on each rail, give a bit of headroom and bingo you have your AC secondarys. (and if you know the secondary DC values you can rig up a PSU to gauge current requirements needed.)
Heck I'm even run a dual primary on one of it's intact 120 windings on a variac (when one was damaged) to get the secondarys in the past.
I wouldn't bother with it personally but that's just me
Just to clarify, I spotted on the 7020i manual there were two 120 primarys (one with a tap for 110), so that would say there should be 5 wires coming from the primary side
If there's six then it could be an undocumented thermal fuse connection that's now blown and O/C, but I couldn't quite see that from the photo's (which have now disappeared anyway?!)
If there are indeed six wires from the primary then I suggest emulating the blown thermal fuse by bridging at the pcb to regain the ~16ohms total primary impedance. The amp (if no faults) should now power up for you to check AC secondarys
I'm not suggesting return to customer in this state , but it would give you opportunity to get the secondary voltages (and currents if you break each winding in turn to measure current)
As for working out the secondarys without the TX working , one could simply work back from the DC levels on each rail, give a bit of headroom and bingo you have your AC secondarys. (and if you know the secondary DC values you can rig up a PSU to gauge current requirements needed.)
Heck I'm even run a dual primary on one of it's intact 120 windings on a variac (when one was damaged) to get the secondarys in the past.
I wouldn't bother with it personally but that's just me
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Transformer Disassembly
Various stages of the NAD 7020i transformer disassembly:-
And a close-up view of the Primary connections:-
With the expert help of Forum Member Alan4411 we've deduced that the BLACK wire, the only one with an internal connection problem, must be linked to a thermal cut-off or fuse of some type?
Various stages of the NAD 7020i transformer disassembly:-
And a close-up view of the Primary connections:-
With the expert help of Forum Member Alan4411 we've deduced that the BLACK wire, the only one with an internal connection problem, must be linked to a thermal cut-off or fuse of some type?