One side of a DPDT relay failing?
« on: July 29, 2012, 06:51:40 PM »
Have you ever heard of just one side of a DPDT relay failing? I've been going round and round with TC electronics tech support about my BM6a's that have the well know tweeter dropouts. I'd heard the problem could be the speaker protection relay, and tech support, while they still won't give out a schematic or outwardly admit these speakers have/had some issues, finally told me what the common issues were, first being the relay, second cold solder joints in the HF section, third chip MOSFET/HEXFET failure.

I popped open the speaker to check and resolder any suspect connections. I Thought it odd when I noticed a double Pole relay, I guess I thought there would be 2 single pole relays, and thought to myself...can one side fail and the other side still work? My guess with all the vibration that their is most likely a bad solder joint, especially with the symptoms, but I guess it could be any of the options I was given. I was most curious abut the relay possibly only having one side fail, I've never seen this before. I have yet to test it either.


Re: One side of a DPDT relay failing?
« Reply #1 on: July 29, 2012, 08:19:07 PM »
I have this exact same problem with a BM6A. The relay is for speaker protection, one side for each (bass/treble).

I even have a replacement relay ready but I haven't got around to fixing it because the problem only happens on speaker switch on, and I can just twiddle the on/off button a few times and it stays on.

I have never heard of one sided relay fails either, but I could not think of anything else that could be broken. It's mechanical after all. Everything measures perfectly and I actually did go through just about all the solder joints.

Let us know how it goes should you happen to replace that relay.


Re: One side of a DPDT relay failing?
« Reply #2 on: July 29, 2012, 08:58:31 PM »
Of course anything can fail or wear out... especially if switching high current and /or inductance.

Back about 50 years ago, I repaired the family dishwasher when one throw, of one pole, of a motor/cam driven switch contact (to open the water valve solenoid) burned out. Since the switch was double throw but the machine only needed one set of good contacts to work, I pulled out the armature, flipped it upside down and reinstalled it so the good side was now facing the working end, and presto I had a like new switch contact.....

Of course modern relays are not likely to be built so repair friendly or survive you taking them apart and putting them back together again, but they should be easy enough to troubleshoot with a VOM. 

Cancel the "cancel culture", do not participate in mob hatred.


Re: One side of a DPDT relay failing?
« Reply #3 on: August 01, 2012, 12:10:35 PM »
I was discussing this with byoung in private already but an important thing needs to be said: yes, sealed relays can break.

I went ahead and finally replaced that suspect relay. The problem is finally fixed. The broken relay actually rattles inside. That's not supposed to happen with relays sealed in plastic! This particular Omron relay is not available as a replacement and it's long gone obsolete. That's a good thing. Maybe even Omron eventually noticed they have a model that is bound to break and they stopped making it.

This is the part I have now, the one that works:

5A 240VAC
5A 30VDC


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