Hi folks,
I'm totally new here, but have lurked for a while. I'm super new to tinkering with amps, but wanted to see if my problem might be easy enough for a noob to solve. Repair shops in my area want more than the amp is worth in its state to even look at it. But it's been with me since my parents bought it new and I've always loved the look and sound.
Problem started a few years ago after loaning it to someone. He's techy and said he did me a favour by spraying the volume controller as there was some crackling noise. I plugged it in when I got it back and it promptly blew a tweeter in one of my speakers (after a loud noise came out). Then...nothing. No sound from speakers or the headphones.
That was s few years ago now and it's been sitting around collecting dust. I'd love to bring it back to life. I've found a few good threads here on testing what the problem might be, but nothing conclusive. I've tried running the pre-amp out to another amplifier to test and that works! I just can't seem to get that signal to move past the pre-amp.
Any thoughts on what might be going on? I really don't know where to start. (fuses are fine). I've linked to a photo of what I'm dealing with below.
Thanks to any and all for their wisdom.
https://i.ibb.co/cNL2TTV/nad7250pe.jpg
I'm totally new here, but have lurked for a while. I'm super new to tinkering with amps, but wanted to see if my problem might be easy enough for a noob to solve. Repair shops in my area want more than the amp is worth in its state to even look at it. But it's been with me since my parents bought it new and I've always loved the look and sound.
Problem started a few years ago after loaning it to someone. He's techy and said he did me a favour by spraying the volume controller as there was some crackling noise. I plugged it in when I got it back and it promptly blew a tweeter in one of my speakers (after a loud noise came out). Then...nothing. No sound from speakers or the headphones.
That was s few years ago now and it's been sitting around collecting dust. I'd love to bring it back to life. I've found a few good threads here on testing what the problem might be, but nothing conclusive. I've tried running the pre-amp out to another amplifier to test and that works! I just can't seem to get that signal to move past the pre-amp.
Any thoughts on what might be going on? I really don't know where to start. (fuses are fine). I've linked to a photo of what I'm dealing with below.
Thanks to any and all for their wisdom.
https://i.ibb.co/cNL2TTV/nad7250pe.jpg
...spraying the volume controller...
Oh no!With what?
Aggressive cleaning agents are first aggressive, as a means to clear everything out, including the carbon tracks in the volume potmeter, which is a part of the preamp.
I should take it out, inspect it and try to find a replacement. A picture of it (& specs on it) well help.
Oh no!With what?
Aggressive cleaning agents are first aggressive, as a means to clear everything out, including the carbon tracks in the volume potmeter, which is a part of the preamp.
I should take it out, inspect it and try to find a replacement. A picture of it (& specs on it) well help.
You can find the service Manual on Hifi-engine.
Forget the tuner aligments since they should be probably OK.
Perhaps just a little tweaking when it outputs sound.
It could be just a worn pot or oxidized switches.
What happens when You turn the volume pot ?
Can You hear anything when pot shorted ?
Activating switches several times ... nada ?
Start with the basics:
In order not to induce more damage connect a 100W incandescent lamp in series with the amp.
Start by inspecting the PCB for bad / cracked solder pads.
Start by checking the PSU voltages. Cables & connectors.
Check if there is DC on the output before the protection relay since it is probably with protect engaged. Contacts could also be oxidized or relay bad.
Does it even click when powered on ?
Study the UPC1237 protection IC Voltages & datasheet which controls the protection circuit if no DC on the output.
Perhaps a NAD expert knows the common failures and can help You better.
Forget the tuner aligments since they should be probably OK.
Perhaps just a little tweaking when it outputs sound.
It could be just a worn pot or oxidized switches.
What happens when You turn the volume pot ?
Can You hear anything when pot shorted ?
Activating switches several times ... nada ?
Start with the basics:
In order not to induce more damage connect a 100W incandescent lamp in series with the amp.
Start by inspecting the PCB for bad / cracked solder pads.
Start by checking the PSU voltages. Cables & connectors.
Check if there is DC on the output before the protection relay since it is probably with protect engaged. Contacts could also be oxidized or relay bad.
Does it even click when powered on ?
Study the UPC1237 protection IC Voltages & datasheet which controls the protection circuit if no DC on the output.
Perhaps a NAD expert knows the common failures and can help You better.
Hi Styles, there is a moral to lending things 😊 From what you describe my first thoughts are that the amp was left with the volume control at max after cleaning so when you powered up the sound you heard was full power to the speakers. That could be the reason why the tweeter blew which has possibly done some damage to the output stages. It is also possible the amp was damaged before being returned to you.
Having looked at the circuit on HiFi Engine there are two power transformers, one for the tuner and one for the main amp. Both have fuses on the primary side and the main amp has two more on the secondary feeds. There are also some fusible links shown close to the transformers however, you say that the pre amp is working therefore all these must be OK.
Are both output channels dead? Power up the amp (with no speakers connected) and listen for the loudspeaker relay to click in, this should take about 10 seconds. If there is no click then the protection circuit has activated or the power stages are damaged. If the relay kicks in measure the voltage across the speaker terminals of each channel on the back panel. It should be 0.1 – 0.2 and no more. If there is a much higher voltage the output stage is faulty.
I see you have already opened the lid. Take care there are high voltages inside there. With the main power lead removed from the wall socket look at the power transistors, any signs of damage? Close to these transistors will be some 0.22 ohm 3watt resistors, made from white ceramic and about the size of a postage stamp. Are these cracked or blackened? Compare the left and right power boards and see if any components are burnt or look different. Post back if you find anything.
Having looked at the circuit on HiFi Engine there are two power transformers, one for the tuner and one for the main amp. Both have fuses on the primary side and the main amp has two more on the secondary feeds. There are also some fusible links shown close to the transformers however, you say that the pre amp is working therefore all these must be OK.
Are both output channels dead? Power up the amp (with no speakers connected) and listen for the loudspeaker relay to click in, this should take about 10 seconds. If there is no click then the protection circuit has activated or the power stages are damaged. If the relay kicks in measure the voltage across the speaker terminals of each channel on the back panel. It should be 0.1 – 0.2 and no more. If there is a much higher voltage the output stage is faulty.
I see you have already opened the lid. Take care there are high voltages inside there. With the main power lead removed from the wall socket look at the power transistors, any signs of damage? Close to these transistors will be some 0.22 ohm 3watt resistors, made from white ceramic and about the size of a postage stamp. Are these cracked or blackened? Compare the left and right power boards and see if any components are burnt or look different. Post back if you find anything.
Thank you all for the great feedback. Some may be beyond my ability to tackle but I’ve got some fun homework to do. Great community you all have here!