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NAD 7100 Troubleshooting

I took out Q507 again to check it, and P525 is .65 and P524 is 1.8, which sounds to makes sense from above. Q505, Q506, Q507 all are checking okay. I am going to check R520 for kicks at this point, but I need the clicking to stop when all 8 transistors are installed in this section!
 
F503 - F506 are removed, right? Is the DBT connected? If so, does the bulb go on and off with the clicking?

What sometimes happens when the DBT bulb wattage is too low for the unit under test is that when the unit comes on, the current through the bulb causes the voltage at the UUT to drop too low, causing it to shut down. With it shut down, the voltage goes back up and it tries to restart. This cycles causing the 'clicking'. But with F503 - F506 removed, the UUT should not be drawing enough current to cause that to happen.

Assuming you do have the DBT connected, what bulb are you using in it? Confirm it is an incandescent bulb, not an LED.
 
F503-F506 are removed, the DBT is connected with a 100W incandescent (teflon coated) bulb that does not go on, the 75W bulb does go on, but the clicks don't effect it all that much. The clicks do go away without Q505 and Q506, I was assuming the problem lies somewhere in the extra 1.8V
 
The NAD-7100 is a devil. Please remove and test Q507 & Q508. Assuming those are good, then let's reinstall Q505, Q506, Q507, and Q508. That should put it back into a 'clicking' mode. Put your voltmeter on either end of R501and see if the voltage is stable or jumps with the clicking. Now do the same with the voltmeter connected to either end of R627 - check if it is stable or jumping.

The power relay depends entirely on the power supply on the tuner board. The +12 that feeds R501 comes from the Tuner board P555. The signal that controls the relay is applied to P208 and the base of Q500, and comes from the display board Q801 pin 14 (G5). The display board is powered from the tuner. So if it is the power relay that is clicking, then there is an issue with the tuner power supply.

The speaker relay is controlled by the protection chip Q605, and *that* is powered from the +/- 18 volts. So I suspect the clicking is the speaker relay.

So let's get it back to the point that it is clicking. Still leave F503-F506 out, but reinstall all the transistors.
 
I think i had a short on Q505 based on bad soldering between the base and the collector. While embarrassing, it's now powered on and not clicking!
 
So how close are we to +/- 24.5 volts on the emitters of Q501/Q502 and +/- 18.5 volts on P524/P525
 
Let me add that I replaced Q504 with 512-KSP2907ACTA
MFG Part No: KSP2907ACTA
ON Semiconductor / Fairchild PNP Si Transistor / Bipolar Transistors - BJT
US HTS:8541210095 ECCN:EAR99 COO:HK

and C513/C514 with RFS-50V102MK9#5
Elna Aluminum Electrolytic Capacitors - Radial Leaded
US HTS:8532220020 ECCN:EAR99 COO:TH
 
Replacement parts should be fine.

Please remove and check Q508 with the diode mode of your DMM. If that tests OK, put it back in circuit and
Check:
Q508 emitter: 0.0 volts
Q508 base: -0.6 volts

Q506 collector should be at that -23.75 volts,
Q506 base should be 0.6 volts more negative than the Q506 emitter.
 
Q508 tested fine, but clicking came back when it was reinstalled. The R627 is fluctuating between 0 and 14.89.

Q508:base 0, collector -18.64, emitter 0
Q506: is BAse-18.6, Collector -23.86, Emitter-18

I am going to reinstall Q508 in the meantime
 
I noticed a solder cracked off from the board on C529 between C529 and Q507, but I put it back after measuring a dodgy 4.7uF. I don't know when the crack happened.
 
So are we pretty close now to +/- 24 volts and +/- 18 volts? We need those to be right before we go any further. If the clicking bothers you (and it might be a good idea anyway for now) lift one end of R625.
 
I believe you have removed and tested the output transistors; Q437, Q438, Q439, Q440, and they were all good.

I'm debating whether to have you power it up without the output devices or the install them first. Since the output transistors were good, there is no reason to suspect a blown driver, so let's put them back in - being sure to get the PNP's and NPN's in the right spots. Do we have any other parts removed (other than one side of R625 lifted)?

Reinstall F503, F504, F505, and F506. Put the impedance switch in the 4 ohm positions, and be sure you have the DBT inline. Cross your fingers and power it up. What does the DBT do?
 
Light went on bright and the receiver turned off immediately. Then I did it again for kicks, and it turned on and the bulb went bright, then turned to low after a while. Fuses are still good.
 
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