Repairing an old NAD power amp

[owieman]

Hello,

I have a NAD 2200 power amp (2-channel, 150w each) which I've had since the 80's. It's served me very well up until just recently when the left hand channel blew.

After closer inspection I found a few burnt resistors, mosfets and ceramic capacitors. Since this is a pretty old amp its no surprise as it seems alot of the resistors are starting to corrode.

Last week I took the NAD amp to an authorized hifi shop where they can repair it, but they quoted me 600-$700AUS to repair! They repair by the hour, and said all the resistors would need replacing aswell. The 2200's are getting snapped up on ebay for that much at the moment.

I'm not very keen on spending this amount for them to repair it, and they said later down the track the other channel could give way as well which I believe after seeing the state of all the components.

So rather than paying so much on getting someone else to repair it, I wanted to know if its possible to do it myself?

I'm very cluey with electronics and have lots of experience with using a thermal controlled soldering iron. I also downloaded a service manual that tells me the type and value of every component in each channel.

My biggest concern is that each component have alot of specific variables. I.E. Ohms, Tolerance, type (carbon/metal oxide/flame proof), Wattage.

e.g. Carbon 1/4W 1KΩ ±5%, Ceramic 50V 1000pF ±20%

These are clearly listed in the service manual for each component. It's just a matter of getting my hands on them really.

So I guess my second question is, is there a good place online where I can find the resistors and capacitors i need to fix my amp?

I'm new here btw, I've been lurking around this forum for a long time reading up, its been great so I thought it would be time to join

Any advise would be greatly appreciated!

 

[robot]

sounds like a very cool project, and most definitely doable. since there are no surface mount components the soldering won't be difficult. if you replace all the components then you should have no need to troubleshoot, assuming you don't make any mistakes.

the manual you got is definitely an asset, and yes the component values and tolerances are important.

unfortunately i can't help you out with an online supplier, i always deal with local shops, but i would also like to know of good online ones.

 

[TLS Guy]

Hello,

I have a NAD 2200 power amp (2-channel, 150w each) which I've had since the 80's. It's served me very well up until just recently when the left hand channel blew.

After closer inspection I found a few burnt resistors, mosfets and ceramic capacitors. Since this is a pretty old amp its no surprise as it seems alot of the resistors are starting to corrode.

Last week I took the NAD amp to an authorized hifi shop where they can repair it, but they quoted me 600-$700AUS to repair! They repair by the hour, and said all the resistors would need replacing aswell. The 2200's are getting snapped up on ebay for that much at the moment.

I'm not very keen on spending this amount for them to repair it, and they said later down the track the other channel could give way as well which I believe after seeing the state of all the components.

So rather than paying so much on getting someone else to repair it, I wanted to know if its possible to do it myself?

I'm very cluey with electronics and have lots of experience with using a thermal controlled soldering iron. I also downloaded a service manual that tells me the type and value of every component in each channel.

My biggest concern is that each component have alot of specific variables. I.E. Ohms, Tolerance, type (carbon/metal oxide/flame proof), Wattage.

e.g. Carbon 1/4W 1KΩ ±5%, Ceramic 50V 1000pF ±20%

These are clearly listed in the service manual for each component. It's just a matter of getting my hands on them really.

So I guess my second question is, is there a good place online where I can find the resistors and capacitors i need to fix my amp?

I'm new here btw, I've been lurking around this forum for a long time reading up, its been great so I thought it would be time to join

Any advise would be greatly appreciated!

The resistors are not burnt from age, but burnt because the output devices have broken down.

Your problem is going to be finding where the damage trail ends. I do not advise you taking on this project unless you are prepared to invest in a FET VOM, a signal generator dual channel scope and Variac. You will have to carry out every test recommended in the service manual and purchase all test equipment mentioned to carry out the tests

I have repaired more than a few amps after these disasters, and you won't repair it by just replacing burnt components.

I can guarantee the output devices and the driver transistors are blown and many if not all the associated diodes.

If there are regulators in the power supply specific to that channel they should probably be replaced also.

There will be some type of protection circuit to prevent DC off set. From its date this is probably some type of TRIAC crowbar circuit. This will have sacrificed itself to protect your speakers from a huge DC voltage. If you don't analyze and repair this circuit correctly it will blow up your repair instantly.

You also have to know how to properly install semiconductor devices. You need to know where to correctly place the insulation devices and using heat sinking compounds correctly is a skill to be learned. You also will require appropriate heat sinking devices to protect components, especially semiconductors, from thermal damage during installation.

I have no idea where to buy components in Australia. In the US I use Digi-Key and Mouser electronics.

If you are prepared to take these steps then go ahead, it is certainly doable on that basis. But be warned, with a major fry up like that there will be no room or tolerance for short cuts or half measures.

 

[gregz]

TLS guy's response was on point. I work for a company that produces electronic circuits, and trying to repair a board by replacing random components without diagnostics (and a circuit schematic) is called "shotgunning." Shotgunning has a low success rate, and is strongly discouraged among our test technicians because as mentioned above, it often burns up the new components until the upstream cause is found.

Your best bet is to start shopping for a replacement amp.

 

[highfigh]

Hello,

I have a NAD 2200 power amp (2-channel, 150w each) which I've had since the 80's. It's served me very well up until just recently when the left hand channel blew.

After closer inspection I found a few burnt resistors, mosfets and ceramic capacitors. Since this is a pretty old amp its no surprise as it seems alot of the resistors are starting to corrode.

Last week I took the NAD amp to an authorized hifi shop where they can repair it, but they quoted me 600-$700AUS to repair! They repair by the hour, and said all the resistors would need replacing aswell. The 2200's are getting snapped up on ebay for that much at the moment.

I'm not very keen on spending this amount for them to repair it, and they said later down the track the other channel could give way as well which I believe after seeing the state of all the components.

So rather than paying so much on getting someone else to repair it, I wanted to know if its possible to do it myself?

I'm very cluey with electronics and have lots of experience with using a thermal controlled soldering iron. I also downloaded a service manual that tells me the type and value of every component in each channel.

My biggest concern is that each component have alot of specific variables. I.E. Ohms, Tolerance, type (carbon/metal oxide/flame proof), Wattage.

e.g. Carbon 1/4W 1KΩ ±5%, Ceramic 50V 1000pF ±20%

These are clearly listed in the service manual for each component. It's just a matter of getting my hands on them really.

So I guess my second question is, is there a good place online where I can find the resistors and capacitors i need to fix my amp?

I'm new here btw, I've been lurking around this forum for a long time reading up, its been great so I thought it would be time to join

Any advise would be greatly appreciated!

"All of the resistors"? I seriously doubt it. Maybe all of the bias resistors, but they're nothing special, aside from needing to be the value required with a good degree of accuracy. MOS-FETs are available and if you can't find the OEM parts, I'm sure some equivalent should work fine. The caps aren't anything special, either. That estimate is awfully high, IMO.