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SX-727 Mono Both Channels after Protection Relay Change

C

ChiefStu

New Member
Help again for a newbie! I changed my protection relay to an Omron LY2F-DC24 and now have only MONO and new noise at higher volumes, immediately after start-up. Switches were cleaned two months ago and again now after the trouble. No difference, get mono. Balance to either extreme still powers both speakers, just at a little less volume on the channel that is supposed to be off. Balance pot was fine before relay swap.

SX-727 that I picked up locally, very clean never messed with and sound great for about two months. Then channel dropouts started and led to a relay change. I’ve read a lot and this site has really helped me and someday hope I can give back. I am not an electronics tech in that I can read and find values on the circuit design sheet. I can follow the components layout diagram and can solder.

After the relay change NO more channel dropouts! But as for the MONO - the balance has no effect or any of the speaker settings. Main amps are fine. Mono comes from either pre-out. Also sounds "noisy" at more than mild volume, where it did not before. New relay solder joints are good, continuity from relay pin to end of all wires is good. Before close up at the swap out, I checked DC Bias and offset, both on spec. Relay clicks on after appropriate pause. The wires, colors and screw location all match to before the relay change.

A day after nothing working, I then pulled the relay out, removed the cover and checked continuity from inside the relay to the distal ends of all the wires. I then with the relay "floating" up on the wire bundle, turned on the unit and watched both sides of the relay move and lock in. I then measured voltage at both inside the relay and at the relay pins to the distal ends of all six wires. I don't know what the measurements should be, but I saw voltage on all legs, at both ends, typically a bit different from side to side on a relay pin pair.

Then at the amp power board where four of the wires from the relay end up, the DC offset was all but "O" Zero on both channels. Then checked the DC bias and it is within norms at 23. I was very careful and did not touch anything, other than to slightly loosen the wire bundle under the relay to get some slack when changing. This unit has NOT been recapped or otherwise repaired when compared to original pics in Pioneer documents and internet pics.

1. Can a relay be bad and cause mono?

2. Could a good relay with good outputs have failed an old part elsewhere?

2. Is the Omron LY2F-DC24 the best for a SX-727 produced in May 1973?

3. Suggestions on measures at pins on boards to begin to trace? I don’t have a signal meter or scope.
 
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You had stereo BEFORE the Relay Change??? And NO STEREO AFTER on ALL FUNCTIONS? Sounds like you wired up the relay incorrectly. Check for a solder bridge between pins 1st. The Stereo / Mono Switch could also be causing problems. You may have to tear it down, and physically clean the connecteor slides with a pink eraser, the re-assemble it.

1.) Yes. But it's only gonna give you one side. The "RELAY" is actually 2 relays (one for each channel). So if one side goes bad it dies(contacts mainly), but the other stays running)

2.) Relay is just an off / on switch operated by a circuit. It won't affect anything down stream unless it's told to. (ie: blown speakers because the protection circuit is gaffed and doesn't open the relay. )

3.) Yes, the LY2F-DC24 is the correct replacement now. It used to be the LY4F, but OMRON redesigned it and it's GROWN too much to fit. See this link https://audiokarma.org/forums/index...-relay-replacement.150439/page-2#post-6759577


On the 727 only connect ONE RCA CABLE from source to LEFT AUX INPUT. Set Stereo/Mono Switch to Stereo. Balance to center, tone controls centered, Loudness off, Tape monitors OFF. Do you get sound from one channel or both. If one channel, swap the cable to the other channel and repeat. If you get both channels, repeat on other channel. Report findings.
 
Thanks for your help again - FIXED IT.
First your input testing found the "mono" sound and noise across both individual channels using the Aux input test. Then loosened the relay to recheck the soldering. From the underside when I was checking relay pin clearance to the metal hole edge, before final tightening (darn larger relay), I touched the wiring loom that I had loosened to provide slack for the first install, and out of the corner of my eye saw a large red wire move! On the rear most large ACH-014 capacitor the top most of three red positives on one pin had cracked off and fallen below the other two, so at a glance it looked hooked up. But with a wiggle it detached. It barely had a tip soldered on, no wrap. Re-soldered properly and tested and yippee full stereo and all switches function!! This wire fed to the Power Amp Board above the cap.

I knew I had not soldered wrong and knew all the switches and pots were working before the relay R&R, so why after the relay swap did I have this instant failure? I felt I caused it, but by only looking at other connections and not gently touching, I missed the fractured connection. Now I know what a partial wire loss from a main cap sounds like - AND I had to go back and rebalance the DC bias adjustment.
Now everything sounds great!
 
Sometimes you gotta look under the rock that's under another rock that's under another rock, to find the problem. Glad you found it.
 
I got a question: I have the same stereo that I been wanting to restore and recap. Which place would you guys recommend to buy the restoring kits including all the capacitors and relays and etc?
Thanks,
 
rudolfo said:
I got a question: I have the same stereo that I been wanting to restore and recap. Which place would you guys recommend to buy the restoring kits including all the capacitors and relays and etc?
Thanks,
Click to expand...
Others here are better sources. I have not had to do board components, still dealing with the Vol Pot likely casing a right channel drop out.
 
rudolfo; kits (good kits that most of us would approve of) are generally NOT available. E-BAY is not to be trusted for electronic parts unless it's something otherwise unobtanium from normal sources, (ie: Germanium transistors for early Solid State stuff then it's a toss up). The best way is to pull the Bill of Materials (BOM) from a SX-727 rebuild, usually from MarkTheFixer (aka MTF) it's gonna be a few years old so it will need to be vetted for updates, superceded parts, etc.

I would start a NEW THREAD and insert the old BOM and ask for it to be vetted. Once it's vetted you can order parts from Mouser or Digikey. The only 727 rebuild I know of that has a MTF list, is this thread and the list is from 2011. MTF may have an updated BOM. https://www.audiokarma.org/forums/index.php?threads/sx-727-has-a-sad-left-channel.385351/
See post #2.

RELAY List is here.....https://audiokarma.org/forums/index...-1010-939-838-et-al-relay-replacement.150439/ Post 39 or 40.
 
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larryderouin said:
rudolfo; kits (good kits that most of us would approve of) are generally NOT available. E-BAY is not to be trusted for electronic parts unless it's something otherwise unobtanium from normal sources, (ie: Germanium transistors for early Solid State stuff then it's a toss up). The best way is to pull the Bill of Materials (BOM) from a SX-727 rebuild, usually from MarkTheFixer (aka MTF) it's gonna be a few years old so it will need to be vetted for updates, superceded parts, etc.

I would start a NEW THREAD and insert the old BOM and ask for it to be vetted. Once it's vetted you can order parts from Mouser or Digikey. The only 727 rebuild I know of that has a MTF list, is this thread and the list is from 2011. MTF may have an updated BOM. https://www.audiokarma.org/forums/index.php?threads/sx-727-has-a-sad-left-channel.385351/
See post #2.

RELAY List is here.....https://audiokarma.org/forums/index...-1010-939-838-et-al-relay-replacement.150439/ Post 39 or 40.
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Great deal and that's a very good information. Thank you so much for being there and I know that youre very knowledgeable about this amp. I will look at the BOM too. Meanwhile and sadly one of the my 6800uf / 50 VDC is going out. I'm trying to get an excellent audio grade (around 32.00 each) but theres one that's promising and its 80mm = 3.15 inches and it will be sticking out of the cover. I really want to get a good one for this part.
.... In reprisal to this recap job, I just made a decision to do it. I need a receiver or integrated that I can trust so I can attach my cassette and reel recorder and a phono so I can record a lot. My old 81 sony is dying and I looked at the inside and its got millions of capacitors.. so thats out of the question especially in making a BOM. Not too long ago, I bought a Yamaha AS701 integrated amp. Its got a lot of power but its not really the sound I'm after for so I decided just to restore the SX-727 anyways I have the perfect speaker for it. I had a nice SX-727 before and I sold it and regretted it because I had my sony and I thought it would run forever. But hands down the pioneer dominates. My brother in law bought the same model back in 1979 and I been listening to that same amp since when I was young and I know exactly how it sounds in a form of an almost new or perfectly dialed amp.
Thank you again... CCG

suzook said:
Get in touch with @EastPoint , he can probably hook you up with a good quality kit.
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Will do and I appreciate the follow-up.
 
Take a look at the KEMET. It looks promising. You don't need an Audio Cap for Power Supply Main caps. And in the SX-727 UKL Nichicon's in the audio circuits work very well. Boutique or Audio grade usually doesn't make a noticable difference in SQ in these receivers. https://www.mouser.com/ProductDetail/KEMET/ALP20A682DD063?qs=gt1LBUVyoHm%2BUBVEZB23dA==

You CAN gut the Can caps and stuff them, maintaining the original casing (alleviates the size problem. The UVR series Nichicon would do well inside the can. https://www.mouser.com/ProductDetail/Nichicon/UVR1J682MRD?qs=KXh8wMBzxN%2Bgtv77A3%2BY2w==
 
Right on. The kemet will fit perfect and its a low esr.Ill put that on my list now. This is definitely an excellent big capacitor!
Thanks,
 
Rodolfo.

I suggest researching a Bill of Materials ( BOM) from earlier restorations, ans and simply dropping it into Mouser or Digikey BOM tools.
Are you located in North America?
 
elvi. I referred him to one of the only BOM's (granted it's more than a couple years old) for the 727 here, asked him to post that BOM and then ask to have it vetted. Chances are @MTF may have an updated BOM in his database.

I also forgot about EASTPOINT.
 
I got the bom and thank you again. There might be a few changes in parts but atleast its already that close, very well narrow my time and help me out so much in getting it. So far I ordered 85% already and a few still looking for it due to the low supplies at mouser. I would pick this any day than parts they sell somewhere else.
But bottom line is, this is going to keep me rolling.
Good thing I got this and I was able to recap my nakamichi cassette deck. I wanna order a bigger tip. However and still It was lightning fast!
Hakko_Desoldering_Gun.JPG
 
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