First timer wants to replace a cap in a hypex PSU - advice?

[kemmler3D]

I have a couple Hypex NC500 monoblocks from Nord Acoustics. One of them fails to power on promptly when it's been off of mains power for a long time. It takes about 20 minutes for it to actually switch on after both switches are on.

I contacted Nord, and Colin North (to his great credit) replied promptly with a diagnosis of a specific cap, along with photos and instructions on how to replace it. It should be noted I told him I was the second owner of these amps, and he replied with a full solution within <24h anyway. So if anyone's wondering about the service over there at Nord, here's a very positive anecdote for you.

Since he didn't have follow-up questions to my inquiry, I assume this is a relatively common issue with a known fix.

My problem: I have no electronics background whatsoever. I know how soldering works (vaguely) and I've seen it done, but haven't done it myself. So I'm at square one, presumably needing to buy a soldering iron, multimeter, any maybe some other stuff?

I think I am happy to own those things for future repair tasks, so if I have to spend a few $$ it's OK.

I also figure I should practice desoldering / soldering on some scrap electronics before going ahead with this one.

But is there anything else the wise members here would advise I do / don't do in attempting my first amp repair?

 

[Rick Sykora]

So, have a spare A700 power supply (just in case) ...

If you post or pm Nord's instructions, can give you an idea of what you are up against. Practice will be key for success but also depends on which cap and where it is located.

If Nord did not already emphasize, allowing the caps to discharge is essential. Sitting unplugged for at least a half hour should do.

 

[kemmler3D]

Here's Colin's reply... seems straightforward enough, but then again, maybe those are "famous last words"...

Replace C38 220uF 35V 105 degree aluminium capacitor
Remove PSU, 6 screws underneath the case.
Remove 6 screws in Aluminium vertical heatsink.
Remove 3 screws underneath the aluminium base holding the edge of the PCB.
Locate C38 red arrows. Desolder apply lots of heat as on a ground plane. Pull C38 out held in place by silicon.
Replace Capacitor ensure correct orientation Positive Negative leaving long legs to bend away from the output transformer.
Rebuild PCB into heatsink.

 

[Rick Sykora]

Thanks, sounds like it is a bit tricky. Will check underside when I have some time.

 

[kemmler3D]

Thanks, sounds like it is a bit tricky. Will check underside when I have some time.

I have a lot of DIY spirit, enough to try stuff I'm not qualified for anyway, and worst case I just need to buy a new PSU.

 

[radix]

You should get a capacitor discharge tool (they are inexpensive). Capacitors can keep dangerous levels of power in them for a while after power off, unless the circuit was specifically designed to discharge them. Maybe the Nord are, I don't know. Anyway, I'd always feel safer putting a discharge tool on them first.

If there are a bunch of small ones in parallel, one contact should discharge them all.

 

[radix]

Also, there's basically 3 ways to desolder something: a wick. a solder sucker, or a vacuum tool. The vacuum tool is the cleanest as it combines a hot tip with a vacuum. If that's too expensive for you, get a decent solder sucker. They are like a spring loaded syringe that sucks the heated solder up. A wick can also work, but generally doesn't get it as clean as the other two.

When you go to resolder the capacitor, a good trick is to put it in, then attach an alligator clamp to one lead at the PCB. This will keep it in place while you solder the other lead.

Just don't overhead things.

You can checkout the helpful links here. There's specifically one on soldering.

DIY Audio 101

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microphone-parts.com

 

[Sokel]

Also make sure not to leave any long solder tails as they can make contact with the heatshink which is always (it should) tied to ground.
Practice a LOT with older crappy boards where caps are in tricky places as this one and make sure to keep a steady hand so you won't desolder anything near.

Make sure to inspect everything with a good magnifying glass after so no remains of solder,paste,etc are left and clean it thoroughly.

Good luck!

 

[alex-z]

If that's too expensive for you, get a decent solder sucker. They are like a spring loaded syringe that sucks the heated solder up. A wick can also work, but generally doesn't get it as clean as the other two.

Specifically get a solder sucker with a flexible silicon tip, it is far more effective than the cheap models.

https://www.amazon.com/Engineer-SS-02-Solder-Sucker/dp/B002MJMXD4

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Another tip is add more solder to the components before you remove them. A larger thermal mass means more time to position the solder pump. Same reason why it is best to not trim component legs until soldering is complete.

When you are done clean the board with a soft brush and isopropyl alcohol. Most flux used in soldering is corrosive. If you are having trouble soldering you probably are not using enough flux, it removes oxidization.

Make sure you have a temp adjustable iron, not a generic one. Different types of solder have different melting points.

Use a properly sized tip for the joint you are working on, this will help you avoid excess temperature.

Always tin your solder tip after cleaning, and clean it regularly with brass wire while working. The solder protects the tip from oxidization and acts as a thermal bridge.

Always heat the component/pad you are working on and feed solder onto the joint. Do not feed solder onto the solder tip, soldering is closer to welding than painting.

 

[SIY]

Super important: make sure the + and - terminals of the cap are in the correct holes. Otherwise you will become an alchemist and transmute silicon to carbon.

 

[kemmler3D]

Thanks, great tips so far. Sounds like my shopping list for now is:

• Soldering iron with a small tip / attachment
• Solder
• Solder sucker / wick
• Capacitor discharge tool
• Magnifying glass
• Alligator clips for holding stuff
• The actual capacitor in question
• Multimeter?

 

[alex-z]

Thanks, great tips so far. Sounds like my shopping list for now is:

• Soldering iron with a small tip / attachment
• Solder
• Solder sucker / wick
• Capacitor discharge tool
• Magnifying glass
• Alligator clips for holding stuff
• The actual capacitor in question
• Multimeter?

I updated my previous comment with more advice, but here is some other stuff.

A fume extractor, if not working outdoors. You can also build your own, a box fan + furnace filter is overkill but cheap.

Full sized helping hands. I like this 6 arm model, it is big enough to work on amp or keyboard PCB's.

Amazon.com

For solder, I would specifically recommend 60/40 or 63/37 for beginners. Lead free takes higher temps and doesn't flow as easily. For sizing, don't buy over .8mm. Big stuff is meant for soldering pipes and stained glass.

 

[radix]

Super important: make sure the + and - terminals of the cap are in the correct holes. Otherwise you will become an alchemist and transmute silicon to carbon.

It can be helpful to mark the existing cap with like a red sharpie, then take a picture so you have a permanent record of the - lead orientation. Most (all?) polarized electrolytic caps mark the - lead with a stripe down the side.

 

[Sokel]

Thanks, great tips so far. Sounds like my shopping list for now is:

• Soldering iron with a small tip / attachment
• Solder
• Solder sucker / wick
• Capacitor discharge tool
• Magnifying glass
• Alligator clips for holding stuff
• The actual capacitor in question
• Multimeter?

Also soldering paste,makes things way easier.
Here's a good one:

https://www.amazon.com/Kester-EP256-Solder-Syringe-Dispenser/dp/B006UTCYM2

 

[MCH]

As I newbe diyer camerade, my advice is not to do it yourself, unless, as @Sokel pointed out, you practice extensively beforehand, and even after that... This small repair lights a few red alerts:

It is your first one
+ Chances are one of the terminals goes to ground = perfect for a cold solder
+ it is in a mains powered power supply if I am not mistaken.

Only 1 and 3 should be enough to reconsider doing it yourself imo. Once you buy all the tools you will be at a similar expense of paying someone to do it for you. Think about it.

 

[MaxwellsEq]

+1 on practice, practice, practice. And practice over several different days, it's surprising how things work out well one day, but not the next. You can buy very cheap tag strips and prototype boards to solder components to and then desolder them.

Soldering is a useful skill to have, you get the freedom of making your own cables exactly how you like them

 

[Rick Sykora]

Good news is the target cap has lots of space around its pads and some decent access top side. There is a dab of rtv you will need remove as this will be key to pulling it out cleanly. Also, would not add any solder, but do use flux paste to help desolder. The pads are small so important not to overheat them. When you remove to bottom plate, there are washers and other small parts. Be sure they are all tracked and put back. Not much worse than a stray metal part to ruin your repair attempt.

Do wear googles both soldering and during power up after repair. Would also have some baking soda nearby in case something goes awry, and you need to deal with electrical fire. After repair, only wire AC power to the module to test. If there are any new problems, you will avoid exposing the other boards to potential damage. After that, let the SMPS discharge and complete the wiring. If you do not, you may arc the pins on the 6-pin power connector to the amp boards.

 

[kemmler3D]

This is all great advice, thanks to everyone who has chimed in so far.

I am more wary of trying it myself now, but not totally dissuaded. It's a higher-stakes repair than I'd prefer for my first real attempt, but I had been thinking about getting a soldering setup for quite some time, and so this seems like "a good enough reason" to dive in, despite the risks.

Things I won't do myself: gas line plumbing, water plumbing, or electrical work beyond swapping out fixtures, because those activities have the potential to destroy my house... this doesn't quite meet that threshold.