HI all
I’ve had my mox6 since new and its never left home, so very much in pristine condition. I turned it on after a few weeks of not using it, and the sound is dominated by a loud crackling / distortion sound when I play the keys. The patch sounds are present but drowned out - the same on headphones as well as line out, so not cables or headphones etc. Assume it must be a connection inside that needs cleaning maybe?

Any advice appreciated, not sure where to send it for repair but would prefer to try to do it myself if possible.

Edit; I opened it up and had a look at the pna and jk boards, and all looks totally standard. I didn’t pull off any connectors as they were on quite tight. I ran the service tests and all were OK, including audio out.
Edit2; seems to be linked to master volume ie no distortion at low volume but lots from about 25 percent upwards, and increases distortion with increasing volume.

Guess I need to take to a service centre but thinking of the cost vs value perspective, so would be happy to have a go myself with some advice.

Edit 3 dropped it into a service centre today and hopefully get a diagnosis next week.

Edit 4: looks like main board is faulty and too expensive to economically replace it with a new replacement board. Otherwise its totally immaculate so would consider reasonable offer for spares or repair - UK based, original box and manuals etc.

thanks

David

A little “heads up” about editing a post, as opposed to adding new posts to a thread…
I (and likely other members) search the forums for new posts. Edits don’t change the date of the post, so I never saw the edits and the additional information they provided. The original post didn’t provide sufficient information to determine where the issue originated, including the possibility of something external. To be honest, I didn’t want to get involved when it was not obvious that you might be able to provide more detailed information.

Moving on…
Based on your description, the problem is in circuitry beyond the input to the Master Volume slider. That’s all analog, which with some competence in electronics shouldn’t be too difficult to repair.

Before you give up on the MOX…
What’s your level of experience in electronics? Please be honest. Can you, and are you willing, to make measurements with a multimeter? Are you on familiar terms with a soldering iron? Etc.

Thanks for the reply. I do own a multimeter and also a soldering iron, although never really used them thus far (ie no need to). I’d love to have a go at fixing it as owned from new and still have much uses for it. Service centre said main sound generation board was faulty and report said ‘kept blowing fuses’, quote for replacement was over £500. Also mentioned that power supply board was obselete now, although it works fine. Its not may main keyboard and have lots of patience so actually low risk for me to have a go at a repair.

Please verify that the MOX still has the same symptoms as before you brought it to the “service centre”. There are things that don’t make sense about what you were told.

5pinDIN - 22 December 2020 08:11 AM

Please verify that the MOX still has the same symptoms as before you brought it to the “service centre”. There are things that don’t make sense about what you were told.

Yes exactly the same, a distortion sound that increases with the main volume slider only. Present on main and headphone outs. Keyboard has never been out of the house or opened prior to my quick check, so all looks as new inside. Sound only occurs when playing the keys ie silent otherwise. Sounds like clipping distortion but indicator is in the green.
Thanks David

DavidF - 22 December 2020 09:04 AM

Yes exactly the same, a distortion sound that increases with the main volume slider only. Present on main and headphone outs. Keyboard has never been out of the house or opened prior to my quick check, so all looks as new inside. Sound only occurs when playing the keys ie silent otherwise. Sounds like clipping distortion but indicator is in the green.

OK, good - from what what the servicer said I was wondering if there were further problems.

 

DavidF -

Thanks David

You’re welcome. This time of year things are a bit hectic, so it might be a day or so before I get back to this with some initial suggestions.

OK awesome, thanks again. I’ve undone the screws and can lift the lid OK. I can see the pna board which has the volume slider on. Checked again and up to 2/10 on the volume slider there is almost zero distortion (a lot of normal hiss as speakers are up way loud to hear the keys clearly), distortion starts from 3/10 upwards and is most prominent on high percussive strikes, kick drum, hard chords etc. Everything else works perfectly all controls, screens, sounds etc. Same issue through headphones as well as monitors.

Thanks for the further description. It certainly appears that the problem is not in the digital area, just analog related.

As a first step…
Connect TS (Tip/Sleeve) phone cables to the L/MONO and R main output jacks, with nothing connected at the other end. Disconnect any other cables (USB, MIDI, pedals). With the MOX powered on, measure the DC voltage from Tip to Sleeve at the free end of the cables. It should be low, but let us know what you find.

Also, if you don’t already have it, download the MOX Service Manual, available here in PDF form:
https://elektrotanya.com/yamaha_sy012015_mox6_mox8.pdf/download.html

OK thanks, I’ve got a rolson 27259 multimeter set to 200m and it reads less than 1 on the readout, either 0.00 or fluctuates in the decimal region. Retested and no more than single figures.

DavidF - 23 December 2020 01:04 PM

OK thanks, I’ve got a rolson 27259 multimeter set to 200m and it reads less than 1 on the readout, either 0.00 or fluctuates in the decimal region. Retested and no more than single figures.

I downloaded the manual for that meter so that I’d know what it’s capable of and what you’re referring to. The range you’re using will measure up to (but not including) 200 millivolts DC.

If you’re seeing readings of 0.00~0.09 or so, that’s good. Sometimes the output muting transistors get electrically leaky, causing distortion which tends to worsen with increased volume level. Although it would be very unlikely for all the muting transistors on L/R/PHONES outputs to fail simultaneously, I wanted to make certain. What you measured indicates there’s no problem there.

Next step is to verify that the supply voltage coming into the JK board is correct. That supply is via a connector labeled CN003 (the other end of the cable is from CN3 on the DM board). I’m going to refer to the edge of the JK board having the jacks as its “rear”, and the edge opposite it as “front”. CN003 is a 4-pin one, across the JK board from JK106/MIDI-IN, nearer to (but not quite at) the front of the board. Pins 1 and 2 of CN003 are connected to analog ground, while pins 3 and 4 are the +9volt analog supply. Please measure that voltage. The 20 volt range of the meter should be appropriate.

In order to make it easier to use the meter probes, and hopefully avoid accidental shorts, I have a suggestion. A trick I sometimes use is to attach a small sewing needle to each probe tip. The needle is placed parallel to the probe tip, held in place with a rubber/elastic band wrapped around numerous times.

I suggest making the measurement between pins 1 and 4, in order to keep the probes as far from each other as possible and minimize chance of a short. Let us know what you find.

Note:
Anyone not sufficiently experienced with electronics should refer repairs to qualified individuals, rather than risking damage to their gear and/or injury to themselves.

OK I can see that connector clearly and your suggestion of needles makes sense. Can I simply insert the pointed ends into the wire connectors as I can see some metal connections next to the wires 1 and 4. That way don’t need to take the jk board out or try to remove the connector, which seems tight and not sure if it just lifts off?

DavidF - 24 December 2020 06:57 AM

OK I can see that connector clearly and your suggestion of needles makes sense. Can I simply insert the pointed ends into the wire connectors as I can see some metal connections next to the wires 1 and 4. That way don’t need to take the jk board out or try to remove the connector, which seems tight and not sure if it just lifts off?

My intent is to disturb things as little as possible while taking measurements. So yes, making contact to those points without disconnecting anything would be best. The needles allow for getting into tight spots that are often difficult to access with typical meter probes, but if the probe tips by themselves will work, then that’s good enough.

OK that worked well with needles, reading was 8.92. Tried a couple of times and settled at that figure quite quickly.

DavidF - 24 December 2020 06:33 PM

OK that worked well with needles, reading was 8.92. Tried a couple of times and settled at that figure quite quickly.

Good. I’m going to continue taking this one step at a time. Next is to check the output of the 9 volt delay/filter circuit…

Attached is a portion of the JK board diagram from the SM. On it I’ve Drawn a ”+” sign, and pointed to a lead of a resistor (R056) that I marked with a dot.

With the meter’s negative lead on pin 1 of CN003 and the positive lead on the R056 lead I marked, measure the voltage. It should be at most a few tenths of a volt lower than the reading you previously got at CN003. Let us know.

Click thumbnail to see full-size image

OK done that as described 8.8 or 8.9 is the reading

DavidF - 25 December 2020 10:14 AM

OK done that as described 8.8 or 8.9 is the reading

OK. Before going further with measurements…

First reconnect your speakers or headphones, and verify the problem still exists (it could be intermittent). Presuming it does, let’s determine what happens if the sound source is external. Connect some line-level audio, perhaps another synth, to the MOX A/D Inputs, and see if the distortion is similar to what you got when playing the MOX. If you’ve never used the A/D inputs before, the Owner’s and Reference manuals cover it. However, you may find this support article helpful:
http://www.motifator.com/index.php/support/view/mox6_mox8_setting_up_the_a_d_input

Let us know what the result is.