hypex ncore

[sek]

As the problem of risking a perfectly good PCB during rework seems to affect a couple of users - and hopefully not an increasing number in the future - I thought I'd chime in briefly and share my two cents about how to approach it.

It always amazes me how people risk three-digit-bucks products (computer mainboards, cell phones, audio gear) while desoldering a fraction-of-a-buck component (passives, ICs, interconnections). The way I see it, it's the PCB that should be preserved at all cost, not the component that goes into the bin anyway.

After having this happen to myself a lot - delaminated copper, broken vias, cracked PCBs - I nowadays resort to strictly (and purposefully) destroying the component while going as easy on the PCB as possible.

In most cases, the component in question is either damaged anyway, cheap or won't survive the heat of desoldering - at least not without application of proper specialty rework tools.

Thus, generally speaking, physically decoupling/separating the solder pads from each other is the way to go that I would recommend from my own experience.

An IC is removed by cutting it's legs of (scalpel-sharp knife), then desoldering them one by one.

A through-hole electrolytic capacitor is best removed by pulling the metal can off the electrodes, then desoldering the residual two pieces of wire.

Given how little force/leverage is required in order to desolder a piece of wire either from a pad or out of a hole, the risk of damaging a PCB while doing so is minimal compared to keeping the component fully intact.

Now, with smaller two-pole SMD components, it's different. Trying to crack the ceramic carrier of a resistor or capacitor is very hard on both PCB and tools.

Here I'd recommend applying heat to both pins/pads at the same time, patiently waiting for the solder to start flowing before using any force.

The lead free solder in modern industrial soldering has a very high melting point (and isn't very ductile until just below that). Thus, patience and a powerful soldering tool really are a virtue here.

If the tip of the iron is too small or the power insufficient, a second soldering iron does the trick. For one-of jobs, this can be virtually any tool that won't torch the PCB (even if it's originally intended to solder the gutter).

As a rule of thumb, as long as force is required to dislocate an SMT component at all, it's still too early (read: too cold) to apply force in the first place.

Now, if something bad has already happened to the PCB, not all is lost in every case. Reworking the PCB doesn't have to stop at trying to replace components, it can extend to replacing copper traces and vias.

With a single-layer board, this is straight forward (trace the copper, replace by wire).
With a two-layer board, broken vias can be replaced by fiddling (thin) wire through the broken via and soldering it to the respective copper layers.

With a multilayer PCB, this is - again - different, as only superficial damage can be repaired without requiring extensive knowledge of schematic and circuit.

But most damage on multilayer PCBs will presumably still be superficial (as long as you didn't pry that capacitor through it's holes until the copper came off...).

Again, that's just my recommendation from my own experience.
Every case is different and mileages do vary.

Cheers,
Sebastian.

[sek]

Originally Posted by Paulkouhan

I was thinking the same, but the toothbrush wash did not help.

One of the "pad" of R141 came with the resistor. I dont know if that can be the problem.

The toothbrush alone might not have done the trick, but using isopropyl alcohol (rubbing alcohol) or other PCB cleaning agent might. There's still some residual flux on the PCB that can be removed in order to make things easier.

Both pads of R141 came off (even though the right one in the picture still sticks in place). Both will require rework.

From over here I can't see any vias directly affected by the lost copper. Both pads had traces connected to them, none had a via directly underneath them.

In such a situation I would carefully remove the laquer from the connected signals and find a good spot to solder a thin wire to.

When done precisely, both the via and the trace can possibly be exposed for soldering.

I'd send a message to Hypex' support department, they are generally very helpful in such cases. Maybe they can confirm the degree of damage and some optimal locations for rework.

Good luck,
Sebastian.

[StigErik]

The method for safely removing R141 is really simple: Flood the entire resistor with solder core, and then the resistor will follow the solder iron when you remove it. Simple as that!

[pos]

Originally Posted by ds23man

I know what gainstructure is, been in pro audio for many years.

What I mean is the ncore has an output noise of 25uV and a signal to noise ratio of 125 db. Gain is only 26 db ( most pro audio amps are 36db). So if you get a hiss out of your speakers, the gainstructure before the ncore is wrong.

You have to solve the problem at the source!

I get hiss even without any source connected to my ncore on my 110dB+ compressions drivers (and these are 16ohms drivers...).
Correct me if I am wrong, but reducing the internal gain of the amp will reduce that hiss, whereas reducing the gain before the amp would obviously have no effect (other than reducing any additional hiss comming from the source, of course).

Now about the "why a 200W amp" (100W/16ohms in my case) question...

Well, do you know of any amp that could match the nc400?
The highs are where it shines the most, and the powersupply can be shared, so why choose anything else? (except for the price, of course )
I am still not sure if I will need a supertweeter in my system, but if I do I am sure I will buy another pair of nc400 to power those...

Another candidate would be The Wire LPUHP, but it cannot be get as an assembled kit... (and even the boards are long sold out...).

[Paulkouhan]

Thank you all for this constructive help !

=> sek, StigErik : I understood that yesterday, unfortunatly too late !! I hope it will help the ones that need to remove R141 (to optimize the gain chain )
=> pos : the ncore is a very good amp, and YES 100dB + speakers are very happy with it !!

I get some fast support from Hypex. At the same time I get the nc400 at work to look at it under a microscope.
Same conclusion as Hypex : there was a connection under the pad !!!



I managed to fix it, it was not easy...

And now the Ncores are playing music !

I will need 2 more to drive my bass dipoles. I may let R141 this time as they need more power ...

[Julf]

Originally Posted by Paulkouhan

I managed to fix it, it was not easy...

Great! Well done!

[sek]

Originally Posted by Paulkouhan

And now the Ncores are playing music !

Yay for DIY.

[Regnad]

Originally Posted by dan92075

ok - thanks - that makes sense now!

also, out of curiosity how long and what size is the cable with the NC1200?

They are bi-wired Acoustic Zen Hologram II, about 12 feet long and fat.

[ds23man]

Originally Posted by pos

I get hiss even without any source connected to my ncore on my 110dB+ compressions drivers (and these are 16ohms drivers...).
Correct me if I am wrong, but reducing the internal gain of the amp will reduce that hiss, whereas reducing the gain before the amp would obviously have no effect (other than reducing any additional hiss comming from the source, of course).

Now about the "why a 200W amp" (100W/16ohms in my case) question...

Well, do you know of any amp that could match the nc400?
The highs are where it shines the most, and the powersupply can be shared, so why choose anything else? (except for the price, of course )
I am still not sure if I will need a supertweeter in my system, but if I do I am sure I will buy another pair of nc400 to power those...

Another candidate would be The Wire LPUHP, but it cannot be get as an assembled kit... (and even the boards are long sold out...).

Maybe a L-pad will be the best solution, this is a clear case of a complete mismatch between amp and driver. Use some high quality MOX resistors to soak the power you do not need for this driver.......

[Julf]

Originally Posted by ds23man

Maybe a L-pad will be the best solution

And lose the low output impedance / high damping factor of the amp?

this is a clear case of a complete mismatch between amp and driver

is it? I can see the reasons for why pos wants to use the nc400, and lowering the gain would definitely help in his situation.