Yamaha S08 Synthesizer not outputting in stereo

I am a retired computer geek with a lifelong interest in music and electronics. While I can recognize a well crafted tune when I hear it, sadly my only musical ability is very basic strumming of an acoustic guitar, with no musical writing, composing, or producing ability.

Lately I’ve been visiting the local Salvation Army Thrift Store, searching for vintage electronics, and have repaired DVD players, printed documentation, found replacement remote controls on Amazon, and returned functioning systems back to the Thrift Store for other people to repurchase. The nice people working there recognize me, and let me know if something interesting shows up in donated electronics.

Most of the items I find are between $3 and $20, and I’ve found a 2006 Pioneer VSX-516 AVR, and a very rare 2005 Toshiba D-R4SU DVD-RAM player/recorder, both of which actually still work. So when the 2002 Yamaha S08 Synthesizer came on display with all pedals, power supply, and accessories, I decided to buy it for $250, which is the most I’ve ever paid so far at the Thrift Store.

After wiring it up to the CD input on the VSX-516, searching through my man cave for some 1/4 in mono cables, and trying to play the Demo songs through a pair of Salvation Army Panasonic speakers, I discovered only the R audio was coming out. I’ve since tried CPR-202 Hosa Technology Stereo Interconnect Dual 1/4 in TS to Dual RCA cables, and OneOdio Fusion A71 Stereo Headphones, with similar results,

The S08 manual says the headphones should be stereo, with L/R 1/4 inputs outputting L side for mono. My latest exercise was carefully disassembling the entire S08 (hey, I’m retired and have the time!) where I found the 1/4 in jacks that Syntar sells are all PCB mounted and sealed parts. My soldering skills aren’t as good as they were in my younger days. Before I carefully reassembled everything, I replaced the (probably original 2002) Sony coin battery, which I’m not sure yet what it’s used for.

Everything else (so far) appears to work on the keyboard, and I’m planning on installing the latest Windows 11 Yamaha USB MIDI driver on my cheap Windows Gateway laptop, and try sending some MIDI files, and play around with the Wave Editor. So this is still the most interesting musical thing I’ve worked on in quite some time.

Hope someone finds my blathering interesting.


The Yamaha S08 looks interesting. That’s quite a find.

That battery (typically) keeps RAM alive when the keyboard is off to retain any sequences and sounds stored in memory.

My story is similar to yours. I sound horrible when I play, but I do it for my own enjoyment. (And all I’ve ever done with my Ensoniq SD-1 was to play its demo song…) So long as no one else is harmed we are okay. They leave us alone. No one has accused me of torturing animals yet.

I decided a couple years ago to actually teach myself to read music but haven’t made much progress. Instead, I play with the controls and see what sounds I can make. I got into repairing instead, which is what I’ve wanted to do for decades, and have been enjoying myself.

Sounds like we also share a similar slightly warped sense of humor! As I wait for California to warm up again, so I can play in my man cave that my little brother helped me build in the back of my detached garage a couple of years ago, my multiple ongoing “inner child” projects have temporarily been relocated to the warmer, but somewhat more congested, master bedroom. Salvation Army Thrift Store (SATS) vintage “bright & shiny” electronics goodies keep piling up.

As a Synth Repair specialist, do you have any idea what might be causing my S08 audio problems?

Oh! I thought you had it working after replacing the jacks. I should have read that a bit closer.

I think you’re going to have to trace that audio signal with a scope. Looking at a schematic, I’m seeing two op amp stages following the DAC for each channel. You could have a break anywhere along that chain. Since you don’t have the Right channel coming through the headphones, you’ve eliminated 1/3 of the path already.

Between the two stages of IC16 and IC13, the signals take a detour off the board to the volume control and back. That introduces several components that could cause issue. I would definitely check for a bad connection somewhere along the line.

By any chance, do you have a link to a PDF for the Yamaha S08 Service Manual?

Never mind. I just found it.

I cautiously downloaded the S08 Service Manual PDF from ElectroTanya, avoiding the colorful DOWNLOAD HERE!! crapware buttons covering the webpage. Finding the TEST PROGRAM on page 30, everything passes until T13. OUTPUT-L SOUND on page 33. (Sorry, audio output is dead on L, not R.) So no 13:OUT L Doing with the headphones, but 14:OUT R Doing works fine. As far as I can tell, all the other tests work correctly.

On my cheap Intel i3 Gateway Windows 11 laptop with 8GB RAM from Walmart, I was able to install the latest Yamaha USB Midi Driver that supports Windows 11, and the S08 is recognized as a MIDI device over USB. I’ve also installed the free MIDI sequencer Anvil Studio, loaded up a free MIDI file, and the file appears to play through the S08 Tone Generator, with the MULTI LED flickering in time with the tune. However, even though the default Piano voice plays from the keyboard on the R channel, and I figured out how to switch Host Set from MIDI to USB, I don’t hear any playback of the transmitted MIDI file through the headphones.

So my questions now are:

  1. Is this enough info to identify a specific component on the S08 schematic to check for the dead L channel?
  2. What button or knob do I need to push or turn to hear at least the R channel side of the MIDI file playback?



Yes, I got my copy of the service manual from ElectroTanya too. I hesitate to direct anyone to random websites, but the copy they have is excellent quality.

How old is the synth? 21 years? Keep in mind that electrolytic capacitors drift over time, and it’s possible for one to be shorted out - even if it doesn’t look bulged. There are meters to test them in-circuit but I’m not sold on them yet - A decent one is expensive, and I think it’s cheaper to just replace a cap if I suspect it’s bad.

I’m looking at the top left of page 68 of the manual. This is our signal path from the DAC to the output jacks - and is the only place where the left and right are separate. We want to follow that signal path all the way out to the output until we don’t have a signal. That would narrow the problem down to a handful of parts.

Are the IC’s socketed? It might save a lot of work if simply reseating IC13, IC16, and IC18 cleans up a bad connection. We could also be looking at a bad solder connection.

Are you experienced using an oscilloscope? When I was going to school, oscilloscopes were the must cumbersome piece of equipment. Bulky. Heavy. Cables. (The school equipment was junk, too, but I digress…) But I eventually learned that using one is sometimes the easiest way to narrow down an issue. I now use mine almost as much as my meter.

It looks like test T13 outputs a steady tone. If it doesn’t, you’ll have to keep hitting keys to get a signal while you do the following checks. Since the right channel works okay, you can run the same tests on the corresponding pins using test T14 to get an idea of what the signals should look like.

This is a bit lengthy, but it only takes a couple of minutes.

The first stage in audio amplification is IC16. If we attach one channel of the scope with AC coupling to pin 3, (right channel pin 5) we should see the signal coming from the DAC. The amplitude won’t matter to us as long as we see something of a signal.

If all is good there, move your scope lead to IC16 pin 1. (right channel pin 7) If we don’t see a signal here, then we know we have an issue with this chip.

From here, the signal takes a detour through the volume control. Make sure it is at full volume.

Now we enter the second stage on pin 3 of IC13. (right channel pin 5) A loss of signal here means that it went to the volume control and didn’t come back.

Since we don’t have audio from the main output or headphone jack I’m assuming that there is nothing at IC13 pin 1. It’s possible that a short in either of these two paths could kill the signal. Luckily, removing C16 or C17 will isolate one of them and eliminate it.

Wowzer! Thank you, Kind Sir! I’m making sense of your very detailed analysis of the dead S08 L channel problem, reading the schematic PDF (blown up, on my aging, but still functioning, and originally costing $400 from Best Buy, 25.5" Samsung monitor, to 200%!) on page 68. Electronics correspondence courses, taken in the previous century with the GI Bill, gave me the ability to sort of read schematics, but I was too lazy to apply myself and actually understand or design them.

I will check for socketed ICs, and I’ve also wondered about failing electrolytic caps from 2002. I like the oscilloscope idea, as I’ve seen compact digital versions online for around $100. Recent attempts at using cheap, but supposedly precise, soldering/desoldering equipment, while trying to repair some old flight simulator yoke gear hardware, with broken teeny tiny wires and miniscule PCBs, did not go well, and were sadly abandoned. But I’m willing to crawl around on the floor looking for miniature screws that dropped, magically defying gravity and basic laws of physics, and give it the old arthritic septuagenarian non-college-but-self-educated try.

Any ideas for hearing at least R channel audio output, through the S08 headphones jack, of the MIDI files played back via the USB MIDI connection from my laptop?


P.S. I hope you enjoy the time I take to write a well-crafted amusing late-night paragraph, with commas inserted appropriately. I love doing this!

That page must print out to some huge poster sized paper. I’ve never seen that sent out like that - they’re usually broken down. I zoomed in too and I’m probably lucky that I was able to find that section so quick. Could be scrolling around all week… For what it’s worth, once you have it zoomed in you can tell adobe to print just the current view.

Someone in another thread mentioned the Hanmatek handheld oscilloscopes on Amazon. I’ve got a decent Siglent scope on my desk but I couldn’t pass up a portable scope for $125. It’ll take some getting used to the controls, but the screen looks easy to read.

I did some engineering for a couple years before I found myself making a living by swapping PCs. Even back then, we discussed how important it was to have decent tools. Now that I’m getting back into electronics I’ve picked up some affordable Hakko soldering/desoldering equipment. It makes all the difference in the world.

I pulled a few caps off of a dead DX7 IID. They looked fine, but one of them even measured 100 ohms. Swapped in some new caps and everything came back to life.

Years ago I was repairing a laptop at a customer’s site and dropped one of the screws. Never found it. I eventually went to work for them and just had to go look for that screw again… I knew it had to be long gone. I’m still dropping screws. Worst part I’ve dropped was the other night. Two clear plastic rods that go in a guitar pedal. Couldn’t see them if I was looking at them…

No ideas on the R channel audio. Something to do with the MIDI file? I think I need to look through the user manual. MIDI files can send out multiple parts over separate MIDI channels. I couldn’t get anything to play on a Juno 2 until I switched the channel to universal so you might try that.

It just occurred to me that we could play some games with the hardware. If you lift one of the components from the board in each channel, you could cross one end of them so that the left channel goes through the right channel’s circuitry. Might be easiest to switch a couple wires coming from the volume control board.

Ahhhm … before you going into taking it all apart - read the Uer Manual firs (search for the word “stereo”)

Maybe someone set the PAN to all left or all right … this is occasionally done if there are no stereo options in the surrounding where is is used

I’ve considered that. The MIDI channel breakout on Anvil Studio shows this MIDI file uses multiple instruments assigned to multiple MIDI channels, at various PAN locations from L to R.

This morning my dental implant surgeon began the final installation of my new upper and lower removable dental implant appliances, so I’m pausing my bright & shiny toy work for the weekend, at least, enjoying antibiotics and “happy pills” while I heal up, This all started in October 2022, and still has another month to go.

Thank you so much for your assistance with the S08, and I will keep you up to date on my progress.


Good point!

I’ve been assuming that the test program would override the settings. Can’t really trust that to be true.

I’m recovering ok from my dental implant work that happened last Friday. Last night I read the S08 Service Manual thoroughly to see how disassembly is really supposed to work, and reinstalled a bunch of screws that I should not have removed, then followed the detailed disassembly procedure properly, removing the plate that covers the UM PCB. I then verified that none of the ICs are socketed, which pretty much convinced me that I’m in way over my head to try to fix this audio issue with the dead L channel myself.

After carefully reassembling the entire S08, with only one tiny screw left over(!!), I plugged in the headphones, powered everything on, verified voices still play in the R audio channel when keys are pressed, and Demo songs also still play in the R audio channel. However, after about a minute, the volume level drops very low, and stays there. If I power the S08 off, then back on, this cycle repeats itself. I’m guessing this is further evidence of electrolytic caps way past their sell-by date of 2002.

Last Thursday, I visited Skip’s Music in Elk Grove, which is relocating with it’s larger store in Sacramento this summer, merging in to a giant new location also in Sacramento. Apparently they plan to open up as the largest independent music store west of the Mississippi. Skip’s has been an authorized service facility for many musical instrument manufacturers, including Yamaha, for decades, and the folks in Elk Grove told me that the 2002 vintage S08 I found at Salvation Army for $250 is well worth repairing.

So for now I’ve moved all S08 equipment and documentation back to a corner of my man cave, and will revisit this again when the new Skip’s Music larger combined store opens up.

Thanks very much for the information and ideas that you’ve provided, and I will let you know what happens next.