KRK RP10s Crossover surgery

[barbaroja]

Hi, I got a KRK RP10s to complement my RP8s. However, the crossover in it is not working ok. One side sounds completely different from the other one, even different levels. Changed cables to mogami, no difference. I suspect of a bad crossover. So I opened the unit in search for some flimsy or leaked capacitors, not finding any. Now I think of an upgrade to caps may solve the problem. I am posting some pics so you guys can see what I am talking about.

I have a failry low knowledge of electronics, so I will ask few "basic" things.

This is the complete unit, dissasembled.


This is a board named "RP10S-PRE V2.3". I suppose this is not the crossover. The pots on it control the sub volume (left) and the other one controls the sub´s cutoff frecuency from 50Hz to 130Hz.


This one is the circuit I believe has the crossover. The XLR outs and ins are placed here, as well as the TRS. All of them balanced.


Any help would be great!

[infinia]

Hi
What are the other detailed symptoms, other than sounds different. Were they dropped, left outdoors, in a hot place, anything like that might help. We need better clues to go by.
I think it would be anti-productive to start replacing parts willy nilly.
My experience has been with hairline cracks in PCB solder joints around component leads that see mechanical stress due to heat cycling or external force. Things esp. like RCA connectors, pots, switches, transistors that are heat sunk, etc. Best to spend time with a magnifying glass and good light.

[barbaroja]

Well, it exactly: Sounds softer than the other side. Also, there is no depth in the sound, like id a blanket was placed between you and the speaker. I had to compensate to -6dB in the back of one of the monitors. Also, it is not cutting down to 80Hz (its fixed cuttoff). I did some test with a sinewave gen, and it goes down to 45 hz with plenty of volume.

The sub is a gift from a friend, so I really do not know if he dropped, or splashed it. Being realistic, I do not think so because it used to be in his studio for some time, but he did not seem to use it much.

I have a coleman audio LS3 switch I am planing to use as a speaker switcher. Some people say you should bypass the crossover in the sub and sum the output of monitors (unfiltered) + sub (filter at 80Hz) so the signal does not get damaged by external crossovers. I feel that it could be adding too much signal in overlappping areas of the spectrum, like 40-80Hz. Any word on this, would be highly appreciatted, too.

I will do a magnifying glass check right now.

[barbaroja]

I checked the board, and there are no shorts or leaked caps. Judging by the pictures, is there a specific place in the board(s) to start checking?

[barbaroja]

Anyone?

[infinia]

Originally posted by barbaroja
I checked the board, and there are no shorts or leaked caps. Judging by the pictures, is there a specific place in the board(s) to start checking?

Your looking for opens not shorts. read closer

"hairline cracks in PCB solder joints around component leads that see mechanical stress due to heat cycling or external force. Things esp. like RCA connectors, pots, switches, transistors that are heat sunk, etc."

Look esp. at parts that are soldered on the pcb and then screwed to sheet metal parts. Look underside for a microscopic crack/s around soldered pins and leads. These are very hard to see with normal vision and are usually intermittant in operation. Likely, if this is your problem and you buttoned everything back up again it might be working.

[barbaroja]

Yeh, I could not find anything unusual. However, I was fiddling with the left channel input XLR, and it happens to be a mechanical failure in the input. Due to this, I connected the sub via the unbalanced RCA connectors, and the problem is not present.

Your advice was right, thank you very much.

I have not fixed it, though, but will do tomorrow

[infinia]

Hi
Glad you found the problem.
Now the surgery part.
1) Check and re-tighten all screws first, esp. PCB and connectors mounting.
2) Re-solder all pins at PCB of all panel mounted connectors.
3) Clean up flux with alcohol and small cotton swabs.

Best