UcD180 Repair

[anomalous]

I have a UcD180 based amp that has failed, and I am trying to determine whether it is repairable, and if so, whether I can do the repair myself.

The cause of the fault was a short or overload in an active crossover unit immediately before the amp in the signal chain, resulting in the explosion of an electrolytic capacitor, C35. not having a circuit diagram, i am not sure what function this cap plays, and whether or not it is likely to be the only problem. there appears to be no other damage to the unit. I'll try replacing that cap and powering up the unit to see what happens.

its a UcD180 Rev 1.0, serial No 0068. the pcb has a date: 14/04/2004 etched on it.

thanks in advance to any help anyone can offer.

[classd4sure]

C35? Right next to the mosfet? On my revision 4.1 thats' a 22uF 63V cap (high ESR) meant for rail snubbing.

Were your modules DC coupled?

[ptwining]

I blew mine up in a similar fashion (nasty DC on the inputs). C35 blew up spectacularly but nothing else was visibly damaged.

I spoke to Kevin who was quite dubious about my chances to repair it so I put the blown UCD's on the shelf and bought another pair.

It would be great if someone could post a board map so we could identify components and have a reference.

Please post your results - I'd be really interested if you can repair it. Maybe I could do the same.

Holding my breath and crossing my fingers for you (and me too)!

Regards,
Tom

[classd4sure]

Now Now!!.. I've been awake for a grand total of 5 seconds and still say, at least remove the remnsance of the cap and test it without it?!?

With DC on the input you probably slammed the output to one of the rails for some extented period, that would have put very high ripple on a high ESR electrolytic... test it without for about 2 seconds and if it works at all just replace it, the cap that is.

[anomalous]

I must admit, given the bang and the amount of magic smoke that came out of the amp, i feared the worst.

after cleaning off the remnants of the exploded cap, it seemed like everything else was undamaged, so i replaced the cap, powered it up, and it works perfectly!

Im glad i didnt have to send it back to Hypex - postage charges between Europe and Australia are out of control.

so, a happy ending - if other people have had similar problems, i encourage them to try replacing the capacitor and seeing if they have any luck.

cheers,

ben.

[classd4sure]

Good stuff!! Thanks for following up here too, I figured it would be OK.

Just make sure whatever caused the failure in your crossover gets fixed too

Cheers,
Chris

[anomalous]

i dont suppose hypex keeps a version change log somewhere online? i dont know what other differences there are, but on my Rev1.0, that cap was only 50V rated. given its spectacular explosion, i dont think being higher rated would have saved it - in fact it may have allowed something more crucial to fail further down the line.

i'd love to know whats changed in the design, especially since i have the earliest version there is.

these modules are just fantastic. my next project is a UcD400 based amp for my folded horn subs. Its pretty funny when the most difficult thing about building a high quality amp is designing and fabricating the case!

cheers,

ben

[classd4sure]

They don't keep such a log but I think we'd rather they all keep working on nice revisions than posting every change they make.

On version 4.1 as I stated they're 63V, but those also have higher shutdown and current ratings.

Also the reason it blew is the very high ripple current it had to endure while having the output slammed to one of the rails. They're high ESR for snubbing purposes, help damp ringing. High ESR and high ripple current = high dissipation and a fast road to failure.

It very likely did save the larger decoupling caps from the very same fate.

Anyway glad you got it going again, you must be thrilled The 400's will not disappoint either.

[ptwining]

I'm glad for your success!

I simply bought another pair of 180's and am really enjoying the amp - it's fantastic and works like a champ. Actually built a pair of MTMWW floor-standers because my 3-ways couldn't do it justice.

But I have a question about the repair. I can't seem to find the caps easily (unless I order 1000 of them it seems) and when classd4sure says :

at least remove the remnsance of the cap and test it without it?!?

Does he mean that literally or should I put a bridge across the spot where it was or just pull it out and do nothing else?

He's tried to help me before but I am too far behind the curve to be able to fill in the gaps. I hate being an annoying noob but it's a fact. At least I'm trying tho...

I'd kinda like to find out if I fried these suckers before I buy a grillion caps (actually I'm sure I could buy less but my local DIY electronics place has no idea where to get a 63V 22uF cap and the web shops want to sell me a truck-load!)

I know that's probably a dopey question but my training-wheels get in the way of more complex ones...

Anyway, thanks for sharing your experience and a big remote thanks to classd4sure for being patient!!

Best Regards,
Tom

[classd4sure]

Hi Tom,

Yeah I mean it litterally.

Caps block DC (high impedance for DC) and pass AC, (the higher the AC frequency, the lower their impedance, the more AC flows through).

In this case, they go from the power rail, one at the positive and one at the negative, to ground. They pass high frequency noise (ringing brought on by high speed switching transients exciting all kinds of little resonant networks created by circuit parasitic inductances and capacitances, both of a parasitic nature and also intential like other low ESR bypass caps at the power rail inputs).


In order to ensure they don't just add to those resonances, a high ESR cap is used (equivalent series resistance). In other words they use a parasitic value to advantage, that of actually helping to damp the ringing.

By removing the cap totally, there's just going to be some increased ringing. I don't think a harmful amount though, especially just for a two second test at low power.

If it oscillates /switches like normal and plays 2 seconds of tunes you know for certain nothing else is damaged, at which point you can shut it off and find yourself some decent replacement caps.

Under no circumstances should you ever consider jumpering the leads where the cap was installed, that would create a direct short from the high voltage rail to ground, something you'd normally avoid at all costs.

Hope that helps.
Chris