NAD 7240PE Dead Tuner

[seabass23]

I'm in the need of some expert advice!

I acquired a 7240PE for next to nothing. Amp section works great with CD source but tuner is dead. Front panel lights up but no sound at all from the tuner. The FM stereo light never comes on even when tuned to known stations.

I'm no electronics expert but can handle some basic troubleshooting. I checked the output from the tuner power supply transformer. From the yellow wires, I get 5.6 and 5.9V AC. From the blue wires, I get 22.4 Volts on one and 0V on the other (according to my schematic, I think I should see 12.2V on both blue wires). My schematic is for the 7220 but it would seem that they have the same tuners.

Is my problem as simple as a bad tuner supply transformer? Any fixes (other than the obvious replacement), or any other recommended tests to perform?

I'd greatly appreciate any troubleshooting assistance any experts could give. I can forward a copy of my schematic if any gurus are willing to help.

Thanks!
Matt

[nigelwright7557]

Disconnect the output wires from the transformer and check it no load for AC voltages.
This will show if the transformer is being overloaded or not.

[seabass23]

Okay, disconnected the load from the transformer. Ac voltage across blue wires is 24V , AC voltage across yellow wires is 12.7V. These numbers seem to make more sense.

I realize now that I was measuring my voltages to ground before, rather than across the two wires. (I have more experience in the DC world).

I have a good quality multimeter and some basic electronics knowledge, I'd really appreciate any help in determining the next steps in troubleshooting my tuner!

Matt

[seabass23]

I'd still love some help troubleshooting my tuner.

As mentioned before, the pre/amp sections of the 7240 work great. The tuner display lights up but is dead silent and won't lock on to any station.

I think I ruled out the A/C power supply to the Tuner, so i guess I need to start troubleshooting the tuner itself.

I have a tuner schematic for a similar NAD reciever (7130 I think). It looks like the tuner is identical so I've got that to work from. I've noticed about a dozen TP (test points?) on the tuner board. Is there any tests I should be performing?

[whitelabrat]

I recently tried reviving a 7240pe. Replaced almost all of the capacitors in the tuner and preamp sections, and even swapped out some op-amps with good results. The tuner was great for a while then it started having issues recently. It just won't lock in on a channel. I get sound. Seems to need adjustment and perhaps some of the parts I haven't replaced have failed.

The amp section is toast. Might be worth fixing but the heat sink is too small.

[whitelabrat]

I was reading through the service manual. There are quite a few adjustments that can be made. I'm guessing things are out of spec. I don't have much for test equipment but a DVM will at least give a clue. Get the service manual and start measuring.

[gain-wire]

What usually is the problem in amplifier sections (especially in equipment that has had a "questionnable" past) is the power transistors have been damaged. Along with them they can take out the the driver transistors, so you'll have to remove all the transistors (that's at least four per channel: two output transistors in either TO-220 or TO-3 packages and one driver per output transistor) and verify them with a multimeter.

then again it could as simple as the signal links in the RCA Pre-out to Power amp-IN missing...

Whatever the problem is, make sure you have No D.C. on the speaker outputs, Highest level acceptable would be around 100mV, and even that's a bit high.