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NAD 7020i - DOA
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Old 26th September 2021, 07:55 PM   #61
indianajo is offline indianajo  United States
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Manual is in post #2.
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Old 27th September 2021, 10:20 AM   #62
DonaldStott is offline DonaldStott  Scotland
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I previously downloaded and searched through all the manuals linked to in Post #2 above.

But as several Forum members have noted, there are no Secondary AC voltages shown on the NAD circuit diagrams/schematics.
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Old 27th September 2021, 11:05 AM   #63
MikePP is offline MikePP
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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

Last edited by MikePP; 27th September 2021 at 11:08 AM.
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Old 27th September 2021, 03:04 PM   #64
DonaldStott is offline DonaldStott  Scotland
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The Primary connections and their associated colours are shown in the attachment to Post #45 by ALAN4411.

We have established that any fault probably lies with the BLACK wire - there is no chance of repairing this Primary as it is usually the first winding on the bobbin.
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Old 27th September 2021, 04:24 PM   #65
indianajo is offline indianajo  United States
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DC voltage of full wave rectifier is (1.4*Vac)-1.4 v.
DC voltage of half wave rectifier is (1.4*Vac)-.7v
They may run some windings hard so a little higher on the AC voltage.
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Old 23rd October 2021, 12:25 PM   #66
DonaldStott is offline DonaldStott  Scotland
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Default Transformer Disassembly

Various stages of the NAD 7020i transformer disassembly:-

TA.jpg TA_1.jpg TA_2.jpg

And a close-up view of the Primary connections:-

TA_3.jpg

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?
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