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The PFL light is flashing intermediately (no pfl button's pressed)

For the better half of my night tonight, I tried googling/youtubing/askingjeeves (before attempting any teardown) of the inside of a yamaha mg12xu (or even 16xu for that matter). I can not find any guide or information, just two videos showing the same problem I have.

Apparently either a PFL circuit has failed or the buttons went bad and are miss-pressing. I just got this last night (ebay), so I don’t want to open it up yet. (I may open it up before i take it to a authorized yamaha repair center and open it again to see what they fixed) so I may end up making a guide/before and after; if I i don’t get a refund.

If there is anyone out there with any experience on these devices (mixers in general) and how to go about fixing this particular problem; please let me know. I’m a repair tech for a CPR but I do small electronics, I have no idea where to start with this.

Oh, here’s a (not my) video to the exact problem, apparently it’s a known thing:

https://www.youtube.com/watch?v=AGXQ13hL...

Answer this question I have this problem too

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Did you get to fix it? I have the same prolem and don’t know what to do.

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I returned it got my money back and bought new unfortunately. I would have fixed it myself but i didnt and still dont have the time to. The fix was apparently capacitor replacements but ymmv.

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I had this problem with hot summer days. I think it's temperature drift of OP-Amp IC602 (if You have Service Manual). I have eliminated it nearly - it is hard to test it in open form so i soldered there some additional resistors and reassembled it again. On the hottest days it blinks still... but but it is 25 times less common now!

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@Spectra Mi Could you please describe in detail what you have done? I have the same problem, beginning when the mixer is working for about 4 hours. I'm not sure, but I had the feeling that it has something to do with the switch for USB / Line in... I pushed this knob many times and then the flashing stopped and did not reoccur. I will test this the next days again.

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Could You give me Your e-mail address? I'll send You some suggestions about it.

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Hello!

ICM02 is the marking on the schematic diagram of that NJM4565M (TE1). The case type is SOP8 and it contains two OP-Amps. First one is with 1 (Output), 2 (invert. Input) and 3 (direct Input). For beginning I added resistor 91kOhm (or 100kOhm) between bus PFLC and pin 2 (invert. Input) of ICM02. Then grounded PFLC bus thru 6.8kohm resistor. It wasn’t enough like it turned out. Second time I added 300kOhms resistor between -15VDC and pin 2 (invert. Input) to give additional shift to it. All connections are provided within ICM02. Princip is following: if there is no pushed any PFL switches - pin 1 (output) has to be with zero volts. If any of PFL switches is activated - pin 1 (output) changes to negative and crosses triggering level (-3VDC) of the following comparator stage (pins 7, 6 and 5 of ICM02 respectively). Due to temperature drift and may-be something else (like induced noise) sometimes it’s possible to trigger the comparator without switching on any PFL switches. 300kOhms resistor between -15VDC and pin 2 (invert. Input) gives additional drift to not achieve that easily triggering level for comparator.

Upper side of schematic on picture: resistor RM14 is connected to +15VDC (sorry, my mistake - didn’t fit on the picture)

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Thanks a lot! Now Yamaha is playing under test and I'm hope will not goes into PFL untill I press the button :)

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Hello, I have the same problem in a MG12XU. Can you help me and give me more indication about the modification?

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This is a factory default bug from circuit design. I didn't fix it yet (I have only MG16XU SERVICE MANUAL but sure I'll get it also for MG12XU). Common bus (second) from PFL switches goes directly to OP-amp input. +15VDC thru 56 kOhms resistor goes to first PFL switches bus. It would be great to have 10 kOhms resistor from second bus to OP-amp input. And second bus is better to ground through 100...330 kOhm resistor. Default second bus is too sensitive. With hotter days OP-amp's temperature drift causes triggering PFL (IMHO).

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Could you please describe step by step what needs to be done to solve this problem? Thanks

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Please give me You e-mail address. I have some files to send about it (here I can't?)

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djunia555@mail.ru

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I have sent You an E-mail. Hope You'll manage with it. First I added only two resistors (91kOhm and 6.8kohm). It was some time OK. But suddenly one day it blinked again! First I couldn't check it in work within opened case. Second time opened and somehow connected all to check all related voltages in working conditions. Due to temperature and humidity changes OP-amp's IC602 (ICM02, NJM4565M) output voltage in larger range. I had to add 300kOhms resistor to give additional shift to it. It seems now it works OK (two months already). No more blinking PFL without switching any PFL switch! Good luck!

Indrek

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Could you describe where you placed the resistor(s) (or which you replaced) like on which pin of the IC602? I think many more people would be interested as it is a pretty common issue. Perhaps even place the relevant docs in a cloud (like dropbox or w/e) and post a link, I still haven't been able to procure a service manual for the mg series.

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An MG16XU came for the same reason to my shop…with so service data, was really thinking but I think I solved the issue by putting a 200k resistor between pin 2 and pin 4 of IC 602. The random PFL flashing seems to have stopped and is stable for now… will keep under check and update.

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Yes, may-be it’s enough to get good result - it will make voltage shift on IC output about 1.65 volts.

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Hello. So from my understanding, if I add a 200kOhm resistor on pin 2 to 4 on the IC602 it would be enough to fix this damned issue.?

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Is it still stable? Do you have a picture for identifying the right PINs?

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Yes customer hasn't come back with the issue. Working perfectly fine.

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hi Ethan could you share me your email? im onto fix the same model however the IC602 thats as dual op amp circuit, so the 200k resistor you put is on pin 2 (negative input of amp A) and pin 4 (voltage) is that correct? i locate the IC according the service manual is the first of the 3 micro circuits just upside the ON buttons for sub2 and master faders and just down the tail of auxiliar return pots, what power handling the resistor is? i am electronics entusiast but i have poor experience soldering micro components, many thanks

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Hi! I'll try to upload pictures from it. I used ceramic capacitors, non-polar, for 50 volts. I had one more such issue this summer - with extreme high temperature (about 30 degrees C). Then it was right thing to mount also switch I had to use. Leakage current to the bus connected to the OP-Amp inverted input is non-stabile, floating in time. Therefore You never know when it will be in bothering area. Using all resistors with lower resistance will improve it but not guarantee.

Good luck to Your work!

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I have seen this problem with a MG16XU mixer that I regularly use.

This YouTube video suggests adding one 150 kOhm resistor from ICM02 pin 2 (inverting input) to ICM01 pin 4 (-15V).

This seems like a simple fix which is less likely to damage the circuit board because no tracks need to be cut (but you will need to have good soldering skills).

I have not tried the fix myself because I don't own the mixer and I don't have permission to modify it. But as an electronics engineer the fix seems reasonable in theory.

Yamaha MG16XU PFL problem solved

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Pic 1 - Schematic diagram: in Red color are shown added components - 2 resistors. Shown 10 and 100 kOhms, really I put (what I had): 6,8 and 91 kOhms. May-be it's not enough to put 300 kOhm Resistor from -15VDC to common point for other resistors (please look at last picture for schematic). In this Summer with hot weather I had PFL flash again! Instead of 300 kOhm You have to put in may-be 200 kOhm or less. I haven't pics about 300 kOhm Resistor in place nor I don't remember even I put it in also. As pics have here no names I can't say exactly what pic is for what. On one pic is shown Earth Connection Point. It was easier to find it in some other place on PC. Also may-be better to disable PFL with switch (look at last pic, blue color).

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Hello! I have investigated that problem again and found out - there is a leakage of current to the bus connected to the OP-Amp inverted input. I have disconnected it and measured voltage on it: it was +14VDC! And it flows up and down! I have removed earlier placed resistors and connected new - one 51 kOhm resistor from -15VDC to OP-Amp inverting input (2). Also added capacitors (1 microfarad) between that bus/OP-Amp input (2) and Earth (0VDC) and the other one to first OP-Amp feedback (OP-Amp's 1-2, in parallel with RM13 and CM18) and paralleled 56 kOhm Resistor with 51 kOhms (connected from +15VDC to PFL switches, PFC_15). Besides I have mounted a switch (for opportunity if there still a problem) to cut a current from Diode (DMO1) on OP-Amp's output.

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Hi! Could you please tell me which capacitor you used? And how many volts? Polar or non-polar? Did you have a problem after this repair?

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Hi! I'll try to upload pictures from it. I used ceramic capacitors, non-polar, for 50 volts. I had one more such issue this summer - with extreme high temperature (about 30 degrees C). Then it was right thing to mount also switch I had to use. Leakage current to the bus connected to the OP-Amp inverted input is non-stabile, floating in time. Therefore You never know when it will be in bothering area. Using all resistors with lower resistance will improve it but not guarantee.

Good luck to Your work!

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so seems the final answer is cutting the current on the diode at the end of AmpOP pin 7? so my understanding is that despite your efforts arranging the circuit with resistences and cap´s trying the negative current leakage becoming stable (And also understanding that the problem arise when the ic gets hot (high ambience temperature) without definitive results, the best of it is to "take or switch" off the PFL function at all, however since to me the PFL is needed, i am exploring this trend, i will try and let you know, but first before start i would like to ask you: something to worry before start, during in, or when finished? something additional must to know? something else to watch out? one question more, since can not be apreciated at all on your pic number 1 https://guide-images.cdn.ifixit.com/igi/... the yellow cable you connected is to one side of the diode (of course the "rigth" side) so i understand that the diode on that side does not touch the PCB in order to isolate the connection, is that correct? thanks

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My pictures didn't reached here. I'll try once more... but if I choose above "Insert an image" icon it shows all my uploaded pictures. Where are they?

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On schematic diagram (https://guide-images.cdn.ifixit.com/igi/...) on left side the switch "PFL" is already by factory default on place - multiple switces in parallel. Right side is added switch with wire colors - P (punane) - Red, K (kollane) - Yellow, S (sinine) - Blue. Diode D603 is disconnected from the Op-Amp IC602 output (7).

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An alternative to these solutions is to remove ICM02 from the PCB.

This will disable PFL entirely - but for me that's not an issue as I never use it.

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Have anyone tried to remove the ICM02 from the board? Will that work?

I dont need the PFL function.

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If you remove the Ic you still have sort of PFL-function, but the signal will be mixed with master signal in your headphones.

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The problem is one or some of the PFL switches. They are rated 12V but actually there is 15V over the switches which they cannot withstand after months/years of service.

I desoldered all the PFL-switches and voila the problem was gone. I am going to change all 16 switches even if some of them are OK for now.

It was hard to believe this was the problem but 5 or 6 switches had the failure after some time. Minutes to hours.

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is it fixed now by changing the button？ i have the same problem

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Yes the problem is fixed. It can be hard to find switches that fits. You should be aware of pin-distance, switchheight, knob height, knob dimension etc.

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Hi Niels. Did you find a replacement for the switches. All I can find are the Yamaha replacements and they would have the same likelihood of breaking down over time. Full Compass has the same switch for 20 cents cheaper.

https://www.fullcompass.com/prod/260369-...

Both Yamaha and Full Compass have the switches on back order anyway.

Do you have the part number for the switches you used?

Otherwise I'll probably pull ICM02. Thanks

Does anyone have a link to the MG16XU service manual they can send me?

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I don't think this is the problem. The insulation resistance is rated at 500V. The other rating is more like a power rating i.e 12V 0.1A --> 12x0.1 = 1.2 Watts.

I don't think that 15V will be a problem. It will be the opamp input leakage current causing the problem which will be solved by a 150kOhm or 200kOhm resistor conneced to the -15V supply.

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hi there, i have the same problem wih a MG16Xu the PFL for the aux return is turning on randmly, however since seems a problem that becomes unstable with the temperature i was wonder iif there is a some how to put a sort of heat disipator, obviousli the IC currelntly is not designed to operate with a power disipator so any sugestion about? thanks

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Hi.

Don’t know why you believe it is AUX because they don’t have PFL. Maybe you think it’s the FX channel. But I don’t think so. The PFL circuit is a very simple comparator so I don’t believe it is temperature drift in the Op-Amp. There is only a single PFL warning lamp so you can’t say which channel is affected. As described above the PFl-switches are not made for 15 V but 12 V and becomes unstable. So you have to change the switch(es) affected possibly all.

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I think Niels is correct. No way of telling which one is the faulty switch/s. I was going to change out all the switches. This is the best one I could find........unavailable right now......of course.............

https://www.fullcompass.com/prod/260369-...

You might find a better one that's in stock somewhere.

In the end I decided to forget the problem and just live with it. Annoying, yes.

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Thanks for that idea. I try it out and get back to the thread. Since the mixer doesn't start out with a fault, but develops it over time. It is possible that the switches are still the main problem. I'll let you know after I run it for a while.

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Donne will be eternally grateful.
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