RME Fireface 800 - Line Output Caps

[angelo2979]

Hello!
I'd like to ask your opinion about an RME FireFace 800 showing chronic disease with the Electrolytic Capacitors on Line Outputs Signal Path.
We have 2 units in our facility, one has always been perfect, while the other one requires a recap every 1-2 years of intense use... Line Outs start dying, so we have no choice but to replace those caps.

I can't understand what makes those caps wear so often... any ideas?

Here is a picture of the inside, where you can see the caps starting to get wasted:

https://i.postimg.cc/RF5f0t8Y/IMG-5298.jpg

 

[Khron]

What sort of DC voltage (if at all) is on their input side (ie. coming from the circuitry)? And do the devices those outputs connect to, have any DC on them?

Line output capacitors (rarely rated for more than 25V) don't often enjoy getting connected to, say, a mic input with phantom power present.

Also, where were the capacitors that the recap was performed with, sourced from? Those vents look Panasonic-ish, but i've seen crappy Hermei ones with the same vent design.

 

[angelo2979]

Thank you for your reply.
The strange fact is this: it's always been properly connected to Line level devices, where there's no reason to assume there is any DC at all. No phantom, nothing.
Those capacitors are Panasonic, as we recapped the unit.

I think there must be something in the circuit stressing the caps, somehow...
so we should test the caps for DC?

 

[Khron]

The source of those capacitors is still unknown, then? But even if they were fakes, they look quite convincing.

Then again, it's not unheard of for even reliable manufacturers to have bad batches now and again (Nichicon HM/HN from 2006-2007 - or 2001-2004? - come to mind, found in Dell Optiplex GX desktops, or United ChemiCon KZG/KZJ series).

But yes, it would be interesting to know if and what DC voltage they might be subjected to at idle. Should be easy enough to probe at one end of those 75 ohm resistors (marked "75R0", with the track going to the associated capacitor).

And as doubtful as it is, even if the opamps were oscillating for some reason, i still doubt they could put out enough power to cook those capacitors.

What series / value / voltage ratings are they, by the way?

 

[angelo2979]

no sorry for been unclear. The source is well known, as I bought them from mouser. I found the link to the exact product I bought, here it is:
https://www.mouser.it/ProductDetail/Panasonic/EEU-FM1E221?qs=MtOUKumLmnbKI/bDacBg9g==

220uf, 25V as you can see. But we already changed them before, so it's likely a problem that keeps coming back, despite the capacitors we use for the recap.

 

[Khron]

The DC idea would have meant that, for whatever reason, they ended up being DC-biased in the opposite direction to their polarity on the board. That still can't be ruled out, but i'm starting to wonder what shape the power supply is in. They seem to be rather notorious / infamous for failing, one way or another.

 

[angelo2979]

Made some measures. Power supply is giving +15,5v and -16v, I assume the difference is not important. These same voltages I am measuring on pin 4 and 8 of those JRC4580 on output.

DC on the 75Ohm resistors legs going to the caps is around 7-10 mV. It really changes from one channel to another... if I output a Sine it looks like DC changes and oscillates diferently, depending also on the sine amplitude.

 

[Khron]

An oscilloscope would be handy as well here...

 

[angelo2979]

I know ... no access to a scope unfortunately

 

[cyrano]

I've currently got a FF400 on the bench. Need to replace the same line output caps. But this one is almost 20 years old, spent it's life in a fairly hot rack.

You could use the mic input from the other FF800 to use as a scope? Just use one of the new caps to block the DC from the PSU.

The only thing I know that blows caps and PSUs on the Fireface range, is heat. Could it be the bad one is in a hotter spot in the rack?