AU 717 Protection Relay are there better choices?

Scott Muni

Scott Muni

Well-Known Member
Five months ago I finished recapping and general rebuild of this 717. It has been playing ok until a few days ago. Noticed the right channel looses volume and goes out shortly after turning amp on. Increasing volume will bring it back to life. Further investigation, if I lightly tap on the speaker relay case, it will come on.
The relay was replaced during the restoration with Omron MY2-02-DC24. Pretty disappointed that I have to go back in and replace it.
Are there better choices to use here? Plus, I see digikey and Mouser are both out of stock.

Ideas, thoughts and a shoulder to cry on are appreciated.
 
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Interesting, I never had one fail. Panasonic used to make one however looks that that is nla. In a pinch you could sub MY4-02-DC24 by trimming off the extra legs, have done that in the past, they are readily available.
Did you check for cracked solder pads?
 
usedto said:
Are you sure it's not the switch in the back? They're notorious for dropping a channel. Sometimes tapping anywhere on the unit will make the connection - for awhile.
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Switch was removed, disassembled and cleaned during the restoration. Moving it now makes no difference.
 
Overundr1 said:
Interesting, I never had one fail. Panasonic used to make one however looks that that is nla. In a pinch you could sub MY4-02-DC24 by trimming off the extra legs, have done that in the past, they are readily available.
Did you check for cracked solder pads?
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I have poked the solder side with a wood shish kabob skewer, no change. Can't really see well enough in there to check pads. Very light tap to the case of the relay is all it takes.
 
Might be a failing relay driver transistor (TR603) and/or relay diode (D608). Were these replaced during the rebuild?
 
Leestereo said:
Might be a failing relay driver transistor (TR603) and/or relay diode (D608). Were these replaced during the rebuild?
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According to my notes, D608 was replaced with 1N4004T, and TR603 was replaced with KSC945C.
Those would effect just 1 channel? I guess if the coil was not pulling hard enough to fully seat the contacts.
 
My last AU-717 was cosmetically mint but had output problems in one channel. It would be lower than the other channel, and would sometimes come to normal level again if the volume was turned up and back down. I replaced a lot while I was in there, but I am 90% sure it was the relay. The pre-main switch was also bad on mine, but that was fixed first and didn't fix the problem.

I read that some people have cleaned contacts on the original relay by removing the clear top, damping a strip of paper with Deoxit (D5), and using it to wipe the contacts. But new relays were still available when I did my rebuild so I just ordered one.
 
Since both D608 and TR603 have already been replaced, the relay may be at fault. Was ZD601 replaced?
 
ZD601 was replaced with 1N5234C.
Increasing volume will cause it to come back. That's why I'm pretty sure (guessing) it's the relay contacts.
 
I will double check solder joints. I'm working on the 331, so will update when that's done .

Thanks guys!
 
MIJ_Pioneer said:
Sounds exactly like the issue I was experiencing recently. It was a cold solder joint and my board was flexing a bit due to missing some screws securing if to the bracket.

Relay was not the problem. Measure across the contacts when engaged to note before / after attempting fixes to see if your fix attempt improved anything.

https://audiokarma.org/forums/index.php?threads/au-717-chances-of-a-bad-modern-omron-relay.986159/
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I didn't notice until you posted this link that the OP was suspecting an *already* replaced relay -- I should have read more carefully! I would also doubt the relay was the issue in that case. But to avoid the hassle of having to take 2663 out multiple times, maybe there's some experimentation that can be done.

You mentioned measuring the relay, but would need to have voltage applied to close the contact. That made me think of another approach I used. Last year I bought a pair of speakers that came with a B&O Beocenter 9500, and it had the same problem with one quiet channel until the volume was raised. I suspected the relay, but it was on a board that was tricky to remove. To rule it out (or in) I soldered temporary jumpers across the relay in/out for each channel on the back of the board. It played perfectly then, so I knew the (original) relay was a dud. Unfortunately that meant having to pull it, which was another story.
 
Before you condemn the relay, don't forget the speaker selector switch - the signal to the speakers runs through that too, and the contacts can get very oxidised.

I have experienced one bad 'new' MY4-02-DC24, I found it by accident almost, as I decided to check it as I had done with the old one to confirm it needed to be replaced. So I got the cover off and gave it the contacts a clean with DeOxit soaked strips of paper trapped in the contacts and pulled through to get the crud off - the relay contacts were perfect after that. Note you should NEVER use anything abrasive to clean relay contacts no matter how fine it is, unless you are looking for a temporary fix.

Note that MY2-02-DC24 (DPDT) is the relay for the AU-517, and MY4-02-DC24 (4PDT) is the relay for the AU-717 - but you can use either relay in either amplifier. The 'MY4' is a 'drop in' replacement in the AU-717, but you have to cut the 'NC' contact pins off for its use in the AU-517. (or drill the PCB).

Finally, if you have lost confidence in the Omron relay, some have used a 'Finder' relay with success, I am sorry I don't know the type number of that relay off hand.
 
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I restored a Kenwood KA-7100 that once sold, came back to be for dropping channels. It turned out to be the brand new Omron relay had dirty contacts. Now, I'm wary/leary of just replacing them for the sake of. And even new relays get their contacts cleaned now.

Interesting that the relay I used was "designed in Japan, made in China". Omron make the same relay with an LED indictor that is made in Japan. Not sure if there are any differences, just pointing that out.
 
Relay problem
I had similar problems with new Omron relays. My undersgtanding is that the new ones are "general Purpose" relays, not as robust as the originals. I just rebuild the original, and have no problems.

The original au717 relay shows as a DPST, or DPDT, but has special dual contacts internal for each pole. (smaller contact and larger contact per side)

Take the cover off
Remove the spring
Slide the contact plate out
Use a pink pencil eraser to polish the contacts
Then form (cut) the eraser so that you can use it to polish the stationary contacts
I then spray the contacts with deoxit gold, wait a few minutes, and spray off any residue
I reassemble contact with the spring, and manually close the contacts as what would happen when energized
Make sure you see the contacts bend a little. If you dont really see that, lift out the contact plate, and ever so lightly, bend the contacts evenly so they there is a very slight bend when you manually close the relay contacts. This bending action "wipes" the contacts, and is necessary to keep them clean.
When finished, (before putting the cover back on, and installing) make sure to test the relay contacts with an ohm meter to make sure you have 0 ohm resistance when closed.
 
I found a Panasonic 4PDT relay that may work (MFG. PN HC4E-HP-DC24V). You may want to check the pin width. They are definitely wider that those of the OMRON MY2/4, but look the same as the original relays.
 
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