NAD 2200 protect light

[Caleb M]

Hi. I am new to this forum and I'm not sure if I'm posting on the right spot or not but I have a NAD 2200 power envelop that my dad had and it's stuck in protection mode.

So far I've done research and found the 2 relays to be a common problem on it but I've unsoldered them and inspected and they are good.

Relays click when you power it on after it's been unplugged for a while but other than that they don't click.

I looked for burnt circuits and I found that C208 and C208 capacitors have some burn marks under them. I pulled them out and tried plugging it in ant protection light went away which leads me to believe the problem is in that circuit. I then replaced the capacitors.

After doing so, same issue. I found that both of the 1 amp fuses (F605 and F606) were also blown.

I jumpered across where the fuses were with a very fine wire to see if the capacitors fixed it, and then both of the capacitors I had just replaced popped.

Any help would be greatly appreciated

Thanks!
Caleb.

 

[AnalogSteph]

I looked for burnt circuits and I found that C208 and C208 capacitors have some burn marks under them.

Are you sure these part numbers are correct? C208 would be a capacitor in feedback that is protected by a pair of back-to-back diodes.

Did you possibly mean C408 and C409? If these go pop, your rectifier D403 is probably toast. Use diode test to check for shorts, it should be a standard bridge rectifier. 1 A, 100 V reverse voltage in a 4-pin DIP, nothing exotic.

 

[Caleb M]

Are you sure these part numbers are correct? C208 would be a capacitor in feedback that is protected by a pair of back-to-back diodes.

Did you possibly mean C408 and C409? If these go pop, your rectifier D403 is probably toast. Use diode test to check for shorts, it should be a standard bridge rectifier. 1 A, 100 V reverse voltage in a 4-pin DIP, nothing exotic.

Thank you for correcting me you are correct both the C408 and C409 capacitors popped. Would I be fine just replacing that D403 rectifier and trying it again?

And if I was to test for shorts where would I do so?

Thanks again for your help it's much appreciated!

 

[AnalogSteph]

Would I be fine just replacing that D403 rectifier and trying it again?

Pretty much. Suddenly getting way excessive voltage out of a transformer secondary seems unlikely.

And if I was to test for shorts where would I do so?

The rectifier is one of these guys internally:

https://www.electronics-tutorials.ws/diode/diode_6.html

You should be seeing a diode junction from the "-" leg to either of the AC ("~") ones, and from them to the "+" leg.

If you happen to have a bunch of 1N400x diodes floating around, you could also build a replacement out of those.

 

[Caleb M]

Pretty much. Suddenly getting way excessive voltage out of a transformer secondary seems unlikely.

The rectifier is one of these guys internally:

https://www.electronics-tutorials.ws/diode/diode_6.html

You should be seeing a diode junction from the "-" leg to either of the AC ("~") ones, and from them to the "+" leg.

If you happen to have a bunch of 1N400x diodes floating around, you could also build a replacement out of those.

Awesome thank you! I ended up ordering a pack of those rectifiers and after replacing it and trying it it blew the 2 big capacitors C408 and C409.

I just replaced them again and I'm not quite sure where to go from there.

Thanks again for any help!

 

[AnalogSteph]

Something very fishy going on there. I would say remove the rectifier and measure what's coming in in terms of AC at the 1 A fuses. Check voltage both between them and between either and circuit ground (wherever you best have access to it, between C408/409, the regulators or C406/407 perhaps). You should be seeing a dual 27.5V secondary, i.e. 55 V~ between the fuses and 27.5 V~ from either to ground. Probably a bit more unloaded.

Has the unit been worked on before?

I can only assume that either some wires from the transformer have been swapped around or the transformer has an internal insulation fault or something (very rare). This circuit should be fed by a secondary with two yellow wires with a grey one being the center tap that goes to ground.

 

[Caleb M]

I will try these things whenever I can get around to and and I'll let you know what I find.

I do not believe that the unit have been worked on but it was my dad's and I don't know an awful lot about it.

Also is there a way I can confirm that the transformer is operating as it should while I'm in there?

Thanks!

 

[Caleb M]

Something very fishy going on there. I would say remove the rectifier and measure what's coming in in terms of AC at the 1 A fuses. Check voltage both between them and between either and circuit ground (wherever you best have access to it, between C408/409, the regulators or C406/407 perhaps). You should be seeing a dual 27.5V secondary, i.e. 55 V~ between the fuses and 27.5 V~ from either to ground. Probably a bit more unloaded.

Has the unit been worked on before?

I can only assume that either some wires from the transformer have been swapped around or the transformer has an internal insulation fault or something (very rare). This circuit should be fed by a secondary with two yellow wires with a grey one being the center tap that goes to ground.

Ok so that top part was a little confusing but I removed the rectifier and was able to power it up without blowing C408/409. I then measured a/c voltage from frame ground (the heatsink) and I got about 29 V~ through both the F605 and F606 fuse with the rectifier removed.

I measured a/c voltage between the two fuses F605/606 and got about 57 V~.

I made the same fuse measurement but instead of measuring from fuse to ground, I measured from fuse to C408/409 and came out with the same measurement as it was to frame ground.

I hope this is useful. Is there a quick way to check the transformer?

Thanks!

 

[Caleb M]

Ok so that top part was a little confusing but I removed the rectifier and was able to power it up without blowing C408/409. I then measured a/c voltage from frame ground (the heatsink) and I got about 29 V~ through both the F605 and F606 fuse with the rectifier removed.

I measured a/c voltage between the two fuses F605/606 and got about 57 V~.

I made the same fuse measurement but instead of measuring from fuse to ground, I measured from fuse to C408/409 and came out with the same measurement as it was to frame ground.

I hope this is useful. Is there a quick way to check the transformer?

Thanks!

Here's a couple just pictures of it in case that helps at all. The unit did sit up in a barn for a good amount of years and we live on gravel so I blew it out pretty good before I tried turning it on

 

[Caleb M]

Something very fishy going on there. I would say remove the rectifier and measure what's coming in in terms of AC at the 1 A fuses. Check voltage both between them and between either and circuit ground (wherever you best have access to it, between C408/409, the regulators or C406/407 perhaps). You should be seeing a dual 27.5V secondary, i.e. 55 V~ between the fuses and 27.5 V~ from either to ground. Probably a bit more unloaded.

Has the unit been worked on before?

I can only assume that either some wires from the transformer have been swapped around or the transformer has an internal insulation fault or something (very rare). This circuit should be fed by a secondary with two yellow wires with a grey one being the center tap that goes to ground.

Sorry I posted a lot just now but a may have found something suspicious around the transformer. Take a look at these pictures.

If you look close, in the first picture you can see the orange and red wire are burnt which looks like a solder iron burn.

In the second picture it looks like on the black and orange wires were the terminal is, clear plastic is a little melted.

 

[Deleted member 48726]

Those caps. Are they okay? -Looks bulgy on the top plastic cover.

 

[AnalogSteph]

I then measured a/c voltage from frame ground (the heatsink) and I got about 29 V~ through both the F605 and F606 fuse with the rectifier removed.

I measured a/c voltage between the two fuses F605/606 and got about 57 V~.

Looks alright to me. You sure you didn't have C408/9 soldered in backwards? Which terminal on which capacitor goes back to rectifier + and - pins? According to the picture they seem to be installed with the minus stripe facing each other, which does not seem correct. Both of them should be installed with minus facing away from the rectifier side, which means that C409 would be installed incorrectly as shown.

While you're in there, verify that wirewrap terminal P-16 is connected to C409(+) = C408(-), and that the grey wire from the transformer is attached to P-16.

Those caps. Are they okay? -Looks bulgy on the top plastic cover.

That's not uncommon and not generally a reason for concern, it's basically just a cosmetic defect. Has something to do with shrinkage, and the bulges should be hollow. The vents for these are at the bottom.

 

[Kbang]

My NAD M3 went into protection mode at startup and I just had it repaired. In my case it was a defective optocoupler. I think it was in the PSU. I hope you find the issue!

Best regards
Kristian Bang, DK

 

[Caleb M]

Looks alright to me. You sure you didn't have C408/9 soldered in backwards? Which terminal on which capacitor goes back to rectifier + and - pins? According to the picture they seem to be installed with the minus stripe facing each other, which does not seem correct. Both of them should be installed with minus facing away from the rectifier side, which means that C409 would be installed incorrectly as shown.

While you're in there, verify that wirewrap terminal P-16 is connected to C409(+) = C408(-), and that the grey wire from the transformer is attached to P-16.

That's not uncommon and not generally a reason for concern, it's basically just a cosmetic defect. Has something to do with shrinkage, and the bulges should be hollow. The vents for these are at the bottom.

THANK YOU SO MUCH I totally didn't pay attention to the orientation of the polarity on the capacitors one was backwards and when I flipped it over it powered up and the relays clicked and protection mode shut off! Got it. Playing through the system and sounds great, except for on the downbeats there's a little bit of fuzziness but I imagine it's probably because of those relays being factory. Maybe the contacts are a little fuzzy. But thank you so much!

 

[Caleb M]

Thanks everyone for the help!
Turns out I installed one of the capacitors backwards and when I flipped it around it worked!
I appreciate the help everyone!

 

[Doodski]

THANK YOU SO MUCH I totally didn't pay attention to the orientation of the polarity on the capacitors one was backwards and when I flipped it over it powered up and the relays clicked and protection mode shut off! Got it. Playing through the system and sounds great, except for on the downbeats there's a little bit of fuzziness but I imagine it's probably because of those relays being factory. Maybe the contacts are a little fuzzy. But thank you so much!

I'm dropping into this thread late so I'm not familiar with all the comings and goings. Have you opened the relays or are they inert gas sealed?