My attempt at fixing the NAD 2700THX

[killdozzer]

1. The Problem

These two potentiometer make so little contact that the channels loose signal for most part. You can barely find two or three positions where the speaker picks up the signal.



2. What I hope for

Is for this to be due to grease, dust, oxidization, patina and I will be able to clean them and everything will work again.

This is not always the case and if I do not succeed I will change the pots, but it will mean buying the solder iron and all. So first’s thing first, I’ll try to clean them.



3. Under the hood

The hot glue gives it away; I’m not the first one to open this amp.



4. First barrier – the tools

“Why don’t we put the nut deep inside of a hole so that conventional tools can’t reach it?!”

I have to pause in this phase until I get the tools that can loosen up the nut of the pot.

 

[<eargiant]

1. The Problem

View attachment 29432

These two potentiometer make so little contact that the channels loose signal for most part. You can barely find two or three positions where the speaker picks up the signal.



2. What I hope for

Is for this to be due to grease, dust, oxidization, patina and I will be able to clean them and everything will work again.

This is not always the case and if I do not succeed I will change the pots, but it will mean buying the solder iron and all. So first’s thing first, I’ll try to clean them.



3. Under the hood

View attachment 29433

The hot glue gives it away; I’m not the first one to open this amp.



4. First barrier – the tools

View attachment 29434

“Why don’t we put the nut deep inside of a hole so that conventional tools can’t reach it?!”

I have to pause in this phase until I get the tools that can loosen up the nut of the pot.

My guess is that the pots in that unit are not sealed. If so, do not take them out if you can access them from inside. Get some Caig Deoxit and use the straw to spray it directly into the pot openings as you turn it several times (unit off and unplugged- then let dry/evaporate).

https://caig.com/deoxit-d-series/

9 out of 10 times that will fix the issue with scratchy/intermittent pots. All pots and switches should be cleaned with the appropriate Caig product.

If that works then at the very least you should get your muti-meter and check and adjust the settings accordingly (DC, etc.).

 

[killdozzer]

It's a yes to most of what you said, but in my parts of the world it's the German products you rely upon so the spray is Teslanol Kontakt und Tuner Spray.

The pots are not sealed but I'm hoping to get inside to get the job done properly. I've had experience before with an amp going to the shop and back several times for the same problem. They would clean the pots and it would work as new, but 2-3 months and it's the same thing all over again. And they charge you each time.

I don't get what you're saying about the multi-meter. Don't tell me that the cleaning can alter the factory settings and properties? Shouldn't the pot just start working as it used to in the first place?

 

[<eargiant]

It's a yes to most of what you said, but in my parts of the world it's the German products you rely upon so the spray is Teslanol Kontakt und Tuner Spray.
View attachment 29444

The pots are not sealed but I'm hoping to get inside to get the job done properly. I've had experience before with an amp going to the shop and back several times for the same problem. They would clean the pots and it would work as new, but 2-3 months and it's the same thing all over again. And they charge you each time.

I don't get what you're saying about the multi-meter. Don't tell me that the cleaning can alter the factory settings and properties? Shouldn't the pot just start working as it used to in the first place?

Hopefully that product has similar ingredients to DeOxit because it really works wonders. Do your research to see what is available in your country that is closest to DeOxit. If that's the product, then by all means use it. Not all "contact cleaners" are the same. Properly cleaned pots should remain trouble free for a long time.

When you do it, be very generous spraying the fluid in the pots. Put a rag under to catch the over-drip. It is also very important to turn the knobs back and forth vigorously all the way many, many times (50+). In essence you are cleaning the wipers in the pot. Repeat the process after all the dirty liquid has dripped out of the pot. Also, wipe off any excess. You want to be thorough because you don't want to be in there every few months doing it all over. Again, the quality of the product used will have a lot to do with this.

As for the amp adjustment, don't worry- the cleaning won't alter the settings but it is good practice to check and adjust them while you're in there cleaning out the amp. I believe that is an older unit and I'd guess it has probably drifted over time. If the settings are off, the amp is not operating as intended and can adversely affect the sound.

 

[killdozzer]

Hopefully that product has similar ingredients to DeOxit because it really works wonders. Do your research to see what is available in your country that is closest to DeOxit. If that's the product, then by all means use it. Not all "contact cleaners" are the same. Properly cleaned pots should remain trouble free for a long time.

When you do it, be very generous spraying the fluid in the pots. Put a rag under to catch the over-drip. It is also very important to turn the knobs back and forth vigorously all the way many, many times (50+). In essence you are cleaning the wipers in the pot. Repeat the process after all the dirty liquid has dripped out of the pot. Also, wipe off any excess. You want to be thorough because you don't want to be in there every few months doing it all over. Again, the quality of the product used will have a lot to do with this.

As for the amp adjustment, don't worry- the cleaning won't alter the settings but it is good practice to check and adjust them while you're in there cleaning out the amp. I believe that is an older unit and I'd guess it has probably drifted over time. If the setting are off the amp is not operating as intended.

This is where we agree. That's the main reason why I'd like to open the pots and wipe of the dirt and not just spray. But if it proves too much trouble, I'll probably do it with them closed.

 

[highfigh]

This is where we agree. That's the main reason why I'd like to open the pots and wipe of the dirt and not just spray. But if it proves too much trouble, I'll probably do it with them closed.

Don't open the pots- they're made to be assembled once. The slot is for getting the spray in, to clean the contacts.

Put the knob on, connect it to speakers and turn it on with music paying before spraying the controls. Since it's open, clean all of the controls and switches. Spray the cleaner in and rotate the controls through their full range several times. Spray more cleaner in and repeat. The second time will flush the control and leave it clean and sparkling. OK, I made that part up but you should hear when the problem stops.

 

[<eargiant]

That's right, don't open the pots. Especially if they are the type I suspect are in there. It's probably a small sealed circular can with a few tiny holes. Spray into the tiny holes. If there is no metal enclosure (an even more basic pot) it's even easier just spray it directly onto the wipers.

 

[killdozzer]

Don't open the pots- they're made to be assembled once. The slot is for getting the spray in, to clean the contacts.

Put the knob on, connect it to speakers and turn it on with music paying before spraying the controls. Since it's open, clean all of the controls and switches. Spray the cleaner in and rotate the controls through their full range several times. Spray more cleaner in and repeat. The second time will flush the control and leave it clean and sparkling. OK, I made that part up but you should hear when the problem stops.

That's right, don't open the pots. Especially if they are the type I suspect are in there. It's probably a small sealed circular can with a few tiny holes. Spray into the tiny holes. If there is no metal enclosure (an even more basic pot) it's even easier just spray it directly onto the wipers.

Thank you for the advice. I'm opening them, though. As I said, I have a long experience behind me of all sorts of different shops doing what you recommend, charging it, only to have it behave exactly the same after 3-6 months. I'm just tired of that. When I brought it in to the shop for like the 8th time to be cleaned (you might remember it, it was the old Technics which I wanted to use as a power amp because of this exact same problem - to bypass all the knobs) they started with some story about the metal inside the pot simply been worn thin over time and that's why they can't do anything (which sounds like bollocks to me, but... until I prove it).

It roughly looks like this:

So the bottom basket should be easy to remove. I am aiming at this:

This is what would satisfy me the most. Clean like new.

 

[slipperybidness]

Thank you for the advice. I'm opening them, though. As I said, I have a long experience behind me of all sorts of different shops doing what you recommend, charging it, only to have it behave exactly the same after 3-6 months. I'm just tired of that. When I brought it in to the shop for like the 8th time to be cleaned (you might remember it, it was the old Technics which I wanted to use as a power amp because of this exact same problem - to bypass all the knobs) they started with some story about the metal inside the pot simply been worn thin over time and that's why they can't do anything (which sounds like bollocks to me, but... until I prove it).

It roughly looks like this:
View attachment 29445
So the bottom basket should be easy to remove. I am aiming at this:
View attachment 29446
This is what would satisfy me the most. Clean like new.

At that point, I would just replace them and be done with it! All that work for an old pot, and then you may or may not correct the problem. If I'm doing labor, I want to know that the problem is repaired.

I know you are not in the USA, but PE is awesome!

Likely a direct replacement:
https://www.parts-express.com/Search.aspx?keyword=pot&sitesearch=true

But......if I'm going to the trouble, I may be inclined to upgrade:
https://www.parts-express.com/Search.aspx?keyword=alps&sitesearch=true

 

[killdozzer]

At that point, I would just replace them and be done with it! All that work for an old pot, and then you may or may not correct the problem. If I'm doing labor, I want to know that the problem is repaired.

I know you are not in the USA, but PE is awesome!

Likely a direct replacement:
https://www.parts-express.com/Search.aspx?keyword=pot&sitesearch=true

But......if I'm going to the trouble, I may be inclined to upgrade:
https://www.parts-express.com/Search.aspx?keyword=alps&sitesearch=true

Yes, but there's a lot of context needed to explain every decision and I don't want to bore people here. The Technics is back at my family house on the island where if you expect to find any pot, you'd be considered optimistic (crazy). And bringing pots here and looking for spare ones... It's too much. I visit home twice a year, it boils down to undoable.

However, I did find a place where I could get spare pots for the NAD, the more the reason why I'm not afraid to go ahead and open them up.

At one point I considered bypassing those pots as their function is something I don't use and have no need for. The reason I gave up is because it would considerably lower the second-hand market price.

My goal is restoring it and not deteriorating it.

Yes, I've been recommended spare-parts several times, but it's not for someone in Croatia. I found them here though.

 

[highfigh]

Thank you for the advice. I'm opening them, though. As I said, I have a long experience behind me of all sorts of different shops doing what you recommend, charging it, only to have it behave exactly the same after 3-6 months. I'm just tired of that. When I brought it in to the shop for like the 8th time to be cleaned (you might remember it, it was the old Technics which I wanted to use as a power amp because of this exact same problem - to bypass all the knobs) they started with some story about the metal inside the pot simply been worn thin over time and that's why they can't do anything (which sounds like bollocks to me, but... until I prove it).

It roughly looks like this:
View attachment 29445
So the bottom basket should be easy to remove. I am aiming at this:
View attachment 29446
This is what would satisfy me the most. Clean like new.

It's possible that the Technics' pots were cleaned with the wrong chemical- some can damage the material on the piece with the three tabs.

 

[killdozzer]

It's possible that the Technics' pots were cleaned with the wrong chemical- some can damage the material on the piece with the three tabs.

That was what I suspected. Just using the dry contact spray and you're doing wrong, let alone some other spray. Anyway, I'm trying to take every precaution to do it right. Taking my time and choosing what comes highly recommended. Also, as I said, If I see force needs to be used to take the ports apart, I'll stop and just try to clean them on the outside.

 

[killdozzer]

Product description:
Application:

Contact spray for cleaning and care of contacts, switches, relays, potentiometers, transistor tuners and channel switches. No after-treatment necessary. Cleans, cares for and protects high-quality contact elements and connectors in a single operation. Do not use under tension.


Properties:

Particularly productive. Produces a micro slide film that sustainably preserves the contacts and keeps them longer. Abrasion of thin metal layers is reduced. No frequency changes. Transition resistances are reduced rapidly. Impregnating against moisture and dirt. Damaged precious metal layers are protected against corrosion.

 

[highfigh]

That was what I suspected. Just using the dry contact spray and you're doing wrong, let alone some other spray. Anyway, I'm trying to take every precaution to do it right. Taking my time and choosing what comes highly recommended. Also, as I said, If I see force needs to be used to take the ports apart, I'll stop and just try to clean them on the outside.

If you can find Cramolin, buy it. It's apparently not allowed into the US anymore, but that stuff was awesome! Caig is what we have access to now (as well as some others).

 

[killdozzer]

Cramolin is the producer, I guess you meant this (I can get it):

 

[highfigh]

Cramolin is the producer, I guess you meant this (I can get it):

Get the kind with lubricant and you should be good for years. For the controls, you understand.....

 

[killdozzer]

Get the kind with lubricant and you should be good for years. For the controls, you understand.....

Sure, sure... That's what I always say. I say "it was for controls your Honor".

 

[killdozzer]

Moving on with the cleaning today. Few shops I visited don't have a wrench that would go into such a narrow deep hole to unscrew a hex nut. Change of plans, I'll try to clean them your way first.

I need some reassurance; Is it really completely safe to clean them this way? Is it really safe to turn them 50 times and more from side to side to make the slider do all the cleaning on the inside and scrape the dirt? Won't this affect them? Isn't that too much scraping?

 

[<eargiant]

Moving on with the cleaning today. Few shops I visited don't have a wrench that would go into such a narrow deep hole to unscrew a hex nut. Change of plans, I'll try to clean them your way first.

I need some reassurance; Is it really completely safe to clean them this way? Is it really safe to turn them 50 times and more from side to side to make the slider do all the cleaning on the inside and scrape the dirt? Won't this affect them? Isn't that too much scraping?

You don't have to turn them that many times. Use your judgement based on the results you get. I only suggested that many turns (gently) because it seems the pots are either really dirty or the previous tech has not been doing a thorough job cleaning them.

You really just want the fluid to get in there and flush all the dirt and oxidation out.

Good luck.

 

[<eargiant]

Since you're cleaning this unit to try and get it up to snuff, I highly recommend you at least check the DC offset measurements at the speaker terminals. It is very simple to do with a multi meter.

Ideally you should have 0 mV +/- 5mV on each channel. If you are +/- 15 mV you are still fine. If the measurements are higher the sound quality will suffer (the greater the variance from 0).