Krell KSA-250 Output Relays - Clean Contacts

SCompRacer

Just started this month, every now and then I was experiencing crackling on left, then right channel with music playing on my KSA-250 amp. Yes, it's an old, complicated amp but when they are working properly, they still sound fantastic.

A Krell tech told me it could be the output relay contacts have some slight corrosion. He suggested closing my fist and banging on top rear corner of amp. Crackling went away! Three choices were offered. $end it for $ervice, build a hefty load bank and apply full tilt power to clean contacts or disassemble and manually clean contacts.

I must admit the load bank-full power fix sounded exciting, but I opted for disassemble and clean. I did it in place in living room as I am older, maybe wiser, and won't carry 140 pounds by myself. (I was reminded of its delivery by Ed, the SRT king during a bad winter storm. As I donned a coat, too late, Ed brought it in by himself)!

I placed some 2x4's under the five footers on amp stand to gain access to bolts holding sides to base. Removed one side at a time. The relays are attached to output board and surrounded by gold-plated copper-beryllium busbars.

A simple 100-watt lightbulb with pull chain was used to discharge those four big caps. That way no sparking when connecting alligator clips. With side on bench, remove the heat sinks, separate driver/input boards, remove straps to get at relays. I took some pics but not all during disassembly. Like the wire colors to the Wego board connectors.

My way to remove plastic relay covers...channel locks, layer of tape on each jaw. Gently squeeze side with release tab, center of cover bows out, pull off. Using sharp probe can sometimes crack cover. YMMV. I cut a thin strip of file folder, wrapped it with a Kimwipe, sprayed some contact cleaner on it. Inserted between row of four contacts and pressed contacts closed, pulled it through a couple times. I Ohm'd contacts out and pressed them closed before and after and there was a difference after cleaning.

You must remove board from speaker output panel to get straps off speaker output terminals. Notice there is a flange on XLR and the XLR soldered to board. There is a fourth hole in XLR. Insert tiny screwdriver and give it a 1/16 turn to release cam lock. Arrow points to tab that holds it together.

Two days now, no crackling when playing music. Huge relief.




Not my amp but shows one compete channel.



Input board removed.

F1nut

For reference the relay is available.
https://www.digikey.com/en/products/detail/omron-automation-and-safety/LY4-0-DC24/365858

pitdogg2

Very nice Rich!

SCompRacer

Yes sir, I'm aware. If contacts did not Ohm out zero I'd go with replacing.

JayCee

Perfect timing! Per usual, nice work Rich, and exactly what I need to see.

A few months ago I was graciously karma'd a broken Anthem MRX-500 from szhleppy with the hope I can fix it and gift to my son for paring w/3.1tl's I gave him.

https://forum.polkaudio.com/discussion/197020/broken-anthem-mrx-500




Haven't had the time to seriously troubleshoot but couldn't resist cracking the case the first night I received it. Powers on but has an oscillation sound. Blasted Vanilla won't let me upload a sound file, so linking the recording on Google Drive:

https://drive.google.com/file/d/1iHxPB41542Eby1EFikOzyh9yK93t6TCq/view?usp=sharing

Wasn't comfortable hooking the receiver up to speakers but letting it idle for a while it goes into protection mode. Did spend an hour or so tearing it down but this monster has layers of boards. Reminds me of a big A$$ HT PC.

Located what I believe is/sounds like it's coming from the relay. Lives on the bottom output board in this pic.


Unfortunately, I can't get to it with power on because it's buried under several boards. Also, not 100% sure I've found the culprit as the sound could be traveling from another area of the receiver. Powered off, I disassembled all the boards to reveal the lower board and relay.



Searching on-line I'm able to find the OM and similar part...but, can't match the "30VDC". Current production looks to be only 28 Amp.

Put everything back together, powered on and it's back to the same condition I received it.

Plan to start my own thread when I have time to work on it but hope you don't mind me asking...can a relay cause this oscillation? Initially, my thought was to disassemble/inspect the relay but don't know if this is a worthwhile attempt to troubleshoot. Your post is like Dejavu re. what I was thinking of doing. Any suggestions re. if this could be the problem and if it can be addressed by cleaning are appreciated?

treitz3

I can't imagine a scenario to where a relay would cause oscillations. FWIW.

Tom

JayCee

Thanks, that's my thought but every time I tried to locate the sound I was back to this part.

txcoastal1

GB=Model number
2C=Form
D24=Coil Voltage 24VDC
P=PCB

So it's a 24v probably peak 30vdc



http://www.handouk.co.kr/english/02_product/general/products/gb-4c.php

JayCee

txcoastal1 wrote: »

http://www.handouk.co.kr/english/02_product/general/products/gb-4c.php

Thanks, I'd found that. I'll be the first to admit I have no problem replacing exact parts but don't have much electronics training/experience outside XO upgrades. If it's not something obvious, simple or a proven solution I'll cry uncle and take it in for an estimate.

SCompRacer

Man, I see complicated! LOL Is relay buzzing? You'd have to check if the relay is getting steady power.

In my case, no power, relay cover off, I could push contacts closed and measure resistance through contacts. I could visually see contact faces, check for pitting. My relays were closing solidly with click and I could physically see that with top cover removed, so no need for me to test circuit powering relay coils.

Using relay data sheet, you could tack solder some different color wires onto board relay terminals and remotely test for steady voltage when powered on and output through contacts, but that's a lot of disassembly/reassembly. You'd have to secure the ends of wires too, mark them for function, don't cross the streams, don't touch, be careful, etc.

JayCee

SCompRacer wrote: »

Is relay buzzing?

Don't think so and, coincidentally, I had this happen on an old Belkin surge protector a few days ago. Distinct buzz, not oscillation. When I opened the case and placed a finger on the relay housing I could feel it. Buzzzzzzzzzzzzzzz!

SCompRacer wrote: »

Man, I see complicated! LOL...that's a lot of disassembly/reassembly...You'd have to secure the ends of wires too, mark them for function, don't cross the streams, don't touch, be careful, etc.

LOL...I'll quote myself....

JayCee wrote: »

If it's not something obvious, simple or a proven solution I'll cry uncle and take it in for an estimate.

EndersShadow

Good luck @JayCee ! I’m rooting for you being able to get it fixed.

@SCompRacer ….. once again stellar work but that’s pretty much expected from you

JayCee

EndersShadow wrote: »

Good luck @JayCee ! I’m rooting for you being able to get it fixed.

Thanks, bud. Still have the HDMI board (or more) earmarked for you in the event it doesn't work out.