Yamaha PSR-12 - AUX out doesn't work

[zbeny]

Hello everybody, this is my first post here

I have problem with my Yamaha PSR-12 keyboard. The AUX out doesn’t work, when I try to connect it to LINE-IN on my PC terrible loud noise continually comes out of the speaker on the keyboard and I get nothing on the PC. The connector also seems to be very sensitive. When I just put my hand near it speakers make noise, not so loud as when it’s connected but they do. Also there is always quieter noise on speaker and headphones output, but I think it comes from the amplifier and it’s normal.

The keyboard was damaged from battery leak. I already removed all the rust and replaced destroyed diode on the keys PCB and one resistor near the main CPU. The output part didn’t seem to have any corrosion on it.

I don’t know anything about analog/audio circuitry, so I don’t know where to start. I have good multi-meter and crappy kit oscilloscope DSO138. My soldering skills are good enough for the trough-hole parts in this keyboard.

Service manual with schematics and board layout is available here: https://elektrotanya.com/yamaha_psr11.rar/download.html
It’s for different model but the hardware is identical.

Please help me troubleshoot and fix this problem.

[Armadillo]

Aux-Out is for connection to expression pedal [external potentiometer].

You could try using the headphone out instead and connect to the line-in of your PC.

[zbeny]

It should work also as audio output, as you can see in user manual here: https://www.manualslib.com/manual/340232/Yamaha-Portatone-Psr-12.html?page=15#manual
In manual it sais that I need PC-2 connection cord. I was searching on google but I can't find anything about it. Also I was in contact with author of this video, you can see the keybord at minute 6, and he told me that he didn't use any special cable.
 
PS: But it's possible that I'm doing somthing wrong when connecting it. It's using CINCH instead of JACK, so I just connected the outer/GND on the cinch to ground on jack and center pin on cinch to one of the channels on jack.

[Armadillo]

Yeah, but you cannot connect it to the line-in of the PC.
If you really desperate,  you can try mic-in of the PC, but I won't recommend it because the impedance will be wholly unpredictable. But if your purpose is just to make sound, you can try it.

[zbeny]

I was trying MIC-IN too, resuld was the same, keyboard was making horrible sounds and the MIC-IN was completely silent. As you can see in the video he was able to record using that output.

[Armadillo]

Have you enable or turn on your PC mic?

Then you are left with using the headphone to connect to PC line in as far as the electronic circuit of the PSR-12 provides.

Otherwise you will need an external buffer for PC line in to work.

Can't comment about others half telling. You can pursue to ask him though.

[zbeny]

Well he told me that he didn't use any special equipment. That's why I think mine must be broken.
Anyway, what should I use as the "external buffer"? I have no idea.

[Armadillo]

Let's confirm your unit is working.

You can try to probe and measure and let us know the results.

Press a 1K tone and measure the points.

I don't recommend external buffer. Its cumbersome. Others may suggest.

Edit: There is infact 1/2 of the opsamp still spare.   

[zbeny]

When I was first time looking at the AUX output with oscilloscope I completely forgot that it’s affected by the volume. So I checked it again and sure enough it works! But even on highest volume it’s weak signal. I tried to capture it with MIC input on pc. It’s possible but there is lot of noise, much more then from the headphones output. Also the speaker on keyboard is making horrible noises when it’s connected to pc.

I included recordings of the noises coming from the speaker. First is when aux is connected to scope, second when it’s connected to MIC input. I also included recording from PC and picture of the signal coming from AUX on max volume.
I still think there is something wrong with it

[ZomBiE80]

What you are hearing is ground-loop noise. My PSR-12 worked perfectly with AUX -> PC, PSR-12 running only on batteries, but not with a wall-wart PSU.

[Armadillo]

What source of power did you use? Is it from battery or from a power adapter?

It sounded like the noises are from a power adapter.

Try the battery and measure the voltage at the point shown. What is the voltage.?

[zbeny]

I was powering it from AC adapter. The battery contacts are completely corroded away, I wired in 9V battery and it works perfectly! No noise from the AUX or speaker!

So is there a way to do this without using batteries?

[ZomBiE80]

check if your keyboards ground plane is negative with PSU negative/ground and keyboard's output ground, if it is, then you can tie them to computers ground. If it isn't, then you need an audio isolation transformer.

[Armadillo]

check if your keyboards ground plane is negative with PSU negative/ground and keyboard's output ground, if it is, then you can tie them to computers ground. If it isn't, then you need an audio isolation transformer.

You can see it from the schematic. But I think even if its just solo using the inbuilt speaker with the wall psu, the buzz is going to be there.

If you want to hook to pc, suggestion for thinker..... the USB is already a good 5V power source..... do at own risks.  But I would say, the best clean source is still the Battery.
For me, it would be just transient inspiration kind of thing, otherwise its back to the storeroom, so no need crack the brain.   

[ZomBiE80]

Yeah, a bit brainfart there, i didn't bother to look at the schematics, as those weren't a direct link, but a .jpg. A proper iron-core PSU regulated might do the trick, modern day switch-mode psu's ALWAYS create problems in analog audio devices, especially older ones.

[zbeny]

So if I add USB connector to the place marked on the schematics and power it from the pc it should work without problems?
Do I have to disconnect the PSU part or will it be fine?
The original AC brick is rated for 3.6W so that shouldn't be problem for USB.

[Armadillo]

Suggestion;

1.0 Your method. OK but hardwired.

2.0 See schematic. Slightly lower than 5v due to diode protection drop but should be working.

3.0 Use a Step Up module from 5V to 9V and no need modify anything. Use to step up module and from it to the plug.

Wire the USB power +ve and -ve **** CAREFULLY ******. Search the web and confirm with meter.

Above are suggestion only for your thinker. So, don't blame me if you spoil the PC USB by wiring wrongly OK.

[Armadillo]

The original AC brick is rated for 3.6W so that shouldn't be problem for USB.

The USB has been used to powered even external desktop audio amplifier/sub woofer, so 3.6W is no problem for that matter.

[Armadillo]

Can it do the mixing, like Bilie Jeans;

[zbeny]

I digged out an old transformer AC adapter and it works great with that. The output is not as clean as on the battery but perfectly usable. I would never thought that the type of PSU could make that big difference.
Anyway thanks for help.