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NAD 7100 Troubleshooting

Tuner has an independent power supply.

The DBT may be reducing the incoming voltage too much and the start circuitry is just cycling. Put F501 and F502 back in (be sure to grab the 0.5 amp ones) and try using a 100W bulb in the DBT. Any different?
 
If you have one of those two bulb adapters, you can use that and install two 60 or 75 watt bulbs.
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I do not, I should be able to update you by Wednesday. I searched my entire place, got a 40W and mini bulbs in my fixtures, so I'm at a loss tonight.
 
Wow, three shops later, I found a 100W (Teflon coated!) but I put it in the receiver. Still clicking :'(. The input at F501 is now reading 26V, and F504 is reading 46. F507 is reading 85 for kicks. I haven't looked at the diagram for a hot minute, but everything is reading a flat 5.5V too few. I'm going to look into that.
 
I switched to 8 ohm impedance and the inputs on the F504 and F507 went to 55 and 90 respectively, F501 went to 27.5, and no more clicking!
 
The impedance switch simply selects a transformer tap. Changing that switch position shouldn't have any effect with F503-506 removed. If you go back to the 4 ohm position, does it again start clicking? The switch itself *could* be bad. How does it feel mechanically?
 
I'm sorry, its Q551, its on the tuner, the heat sink was hot when I turned it off and was lifting for the preamp points. My suspicions are rising that the problem is early on in the amplifier though.
 
The tuner has an independent power supply. While there may or may not be a problem there, the fact that the clicking stops when you blew fuses F501 & 502 indicate the excess current draw is on the +/- 35 volt busses.

Try this.... connect the base of Q507 to ground. That should turn off the +/- 18.5 volt regulators, removing those as a load on the +/- 24.5 volt regulators. Replace F501, 502 and go back to the 75 W DBT. Turn it on and see if the clicking is still there.
 
75W light is *on*, as in lit up? Shouldn't be. Do you get one click when you push the power button - i.e. is the power relay pulling in?
 
not "on" as in lit, but on as in dimly not-off, it looks correct. More importantly, the fuses stayed working, and there was only the one click!
 
Before we go any further, with C529 shorted and the unit 'on', confirm there is +/- 24.5 volts on Q501 emitter and Q502 emitter respectively. Assuming that is good, remove the short from C529....

So it sounds like there is an overload on the +18 or -18 volt line. That +/-18 volts feed the two input switches (Q209, Q210) and the op-amps on that board (Q211, Q305 and Q306). It also goes off-board back to the power amplifier board where it is used by the amplifiers.

My first guess would be the input switches, as these devices seem to have more than their share of failures. Remove Q209 and try it. If that doesn't help, also remove Q210 and give it a try.
 
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