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Relay for Bosch SHX46A02UC/46


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28 replies to this topic

#21 kdog

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Posted 23 November 2011 - 11:43 PM

Might be worth checking with Bruce over at fixyourboard.com and see if they have a solution for you
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#22 kdog

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Posted 23 November 2011 - 11:48 PM

I put the full model number in a subsequent reply


OK - found it and edited title
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#23 fixyourboard

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Posted 24 November 2011 - 01:07 PM

Kdog is correct. The relay is not the problem. The problem is the design of the pc board lands that the relay pins are soldered to. In our shop we repair these by using an "eyelet" (rivet) to re-inforce the connection so that it can sustain the high current required by the heater. You can achieve the same result by using a piece of copper wire to surround the relay pin and flow the solder around the wire, pin and pcb land. You need a decent soldering iron for this but it's not difficult if you have good soldering skills.

Happy TG everyone! (ok, kdog, I know yours was last month -- belated!)

#24 kdog

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Posted 24 November 2011 - 04:34 PM

Thanks for that
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#25 kenahoo

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Posted 26 November 2011 - 12:28 AM

I just ordered a replacement board from RepairClinic.com, should have it in a few days. I also made a couple of photos of the fried board, with 5-year-old son for perspective:

http://imgur.com/uqz4Z
http://imgur.com/d71VP
http://imgur.com/Bsz9P

The offending relay I was thinking about replacing is circled.

Attached Files



#26 kenahoo

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Posted 26 November 2011 - 10:20 AM

In our shop we repair these by using an "eyelet" (rivet) to re-inforce the connection so that it can sustain the high current required by the heater.


That makes sense. I didn't have a good mental model of how the relay could make its pins hot. =)

You can achieve the same result by using a piece of copper wire to surround the relay pin and flow the solder around the wire, pin and pcb land. You need a decent soldering iron for this but it's not difficult if you have good soldering skills.


I have mediocre soldering skills, and a crappy soldering iron (which keeps getting badly oxidized because I can't seem to tin it well), and a relay with no pin left on it. So I think the odds are against me on this one. :blinky:

#27 RegUS_PatOff

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Posted 26 November 2011 - 10:44 AM

... I didn't have a good mental model of how the relay could make its pins hot. =)

bad connections (series resistance) cause heat,
either from bad / broken solder joints / vibration,
or when the actual Contacts in the Relay wear out (get pitted / corroded)

and this thread mentions a replacement Relay from Newark (and other places)
which is actually an NTE Relay R46−5D12−6
http://www.applianto...w-she44c05uc40/
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#28 certified tech group 51

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Posted 26 November 2011 - 12:05 PM

As all repairs go, we need to start with the cleanest solder points...If the old solder cannot be remove, adding new solder to old, contaminated solder, it will fail..... If the leg of the relay is almost burnt off and the controller is removed, there is still life to be had...remember you are saving money....( for some of us, we have more time than money )...There's gotta be a Radio Shack close to acquire some desoldering braid.....Also locate a set of 'riffler' files..(very small files, some with curved ends ) to clean up the post and remove some of the 'solder mask' ( the green stuff)......give it the old collage try........ Us techs do it to keep the customers budget from getting busted plus a good chance of getting a another service call down the road...................................Go Seahawks....

#29 fixyourboard

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Posted 28 November 2011 - 08:01 PM

Good comments. While we replace a LOT of relays, I've found that the blown open solder joint is usually not accompanied by a bad relay. That surprised me at first ... but it makes sense. We often see this problem when the relay contacts are still showing really low resistance (like 8 milli-ohms!). If you do the math, say for a 10 Amp heater, the heat dissipated in the (normal) contact resistance doesn't create a very significant increase in the heat at the soldered pin. Only a few degrees. If the contact resistance goes up by 10X it still doesn't come close to melting the solder at the pin (but there is a heat rise that speeds up the failure mechanism).

I think the cause of this problem is usually a combination of the design of the circuit board pad, the diameter of the hole vs the relay pin, and the parameters set during wave soldering the board at the factory. Sometimes the result is that the cross-sectional area of the solder bridging the gap is not enough to sustain 10 Amps for the lifetime of the machine. I've sawed open relays that came off boards with this problem to inspect the contacts and they usually look good visually, sometimes new looking. Even though the resistance measured out good I wanted to see if they showed visual signs of failing. And usually ... not.

If in doubt, swap out the relay of course. But for a quick fix, your chances are good if you can fix the solder joint. As mentioned above you need a cleaned up surface for sure. The end result needs to be a nice shiny looking solder joint.




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