DENON ep-x07 Electric Piano repair help needed.

[titusdis]

Dear EEvblog users!

I just came across this super forum, (why i didn`t know about this...) and i am looking for some help with a repair project i am stuck on.
The unit is an electric piano`s main board. Unfortunately i didn`t find anything on this instrument on google. Especially not a circuit diagram
The symptoms: unit turns on, no sound comes out.
The amplifier works, tested with a tuner connected to the input. no problems.
I narrowed down the issue to the preamp area of the main board.
When i tickled the marked area`s caps and resistors, the piano sound came back noisy, and squeeky, but audible. not really good S/N ratio, but i knew that the `brain` works.

There is a pcm69au DAC, and 2 NJM 2100 op amps, which makes the line level audio to be sent to the amplifier board.
I already changed all SMD capacitors (the aluminium cap ones, not the small poppyseed-sized ones) no difference.
I can see some black corroded stuff on the board (smd caps vomited???) cleaned as far as i could. changed resistors before the last op-amp, no diff.
I tested the other side of the circuit, it plays something, but high-pitched, not piano-like sample.. (the unit has been made to be mono by some folks before me)
Resoldered the pcm69au, and the 2 op-amps.
resoldered all the components on the marked (red) area.
Took off the smoothing caps (green) of course i lost them, no idea about the values...
I found some circuit diagram for the pcm69, which is really similar to this, so i have some base point.

What i`d like to know that how to test the pcm69 output, without a scope.. (maybe a small piezo speaker???) or test the 2 op-amps...  or what should i expect at the output of them...

I am pretty sure, that corrosion played a big role, i just want to know how to test the circuit furthermore. or maybe i am on a wrong track...

Cheers: Titus (newbie here)

[SMdude]

Hey mate!

First thing you need to do is clean up the board.
You will need to remove and clean/replace each of the components. Most likely there will be deposits under them causing conductivity where there should be none, including the opamp and other ic's.
Make sure you clean up after with a suitable flux remover too.

I repaired a guitar amp that had had cola spiled on it at some point in its life. Unfortunately there was some residue stuck under some electro smd caps, slotted down between some plastic slide potentiometers, that had many through hole pins on them.
After removing the potentiometers and caps, cleaning it all up and re-assembling, it worked like a charm!

Oh, and the little smd caps you have circled are the ic power pin bypass caps. Most likely 100n.

[titusdis]

Well, first of all, thanks for checking out my cry for help!

I am pretty much done with the board cleaning, and resoldering of those parts.
I attached an old picture (before attempt) but i will do an updated one as well.
I found some rotten solder joints, and pads, cleaned them, and replaced the components. But still no luck. I ordered another pcm69, form china, that is another step, when it arrives. i was just curious that could i check the output of that pcm somehow, before those op-amps. and then i would move on to the first op-amp output, an then the second. Maybe i wasn`t paying enough attention on board checking, so i will do another go on cleaning.
But the circuit checks out with continuity, (the traces are connecting the parts) Also tomorrow i will replace those 0805 smd caps, fortunately i had the chance to measure them. Altough one of them gave a weird value. (c116 - 5000 pF)

Fortunately there is another preamp area printed on the pcb with traces and pads, but no components, probably for future upgrade - dual channel whatever... so i can steal the pcb traces (how they connect and so)
Please if you have any insights, let me know!

Thanks: Titus

P.S.: If somebody has a circuit diagram/service manual about it, that would be fantastic! I could find anything.

[SMdude]

You could maybe try using a small earphone and see if you can hear anything when connected to:
Ground(the copper pour between ch109 and ch105) and the + side of ch109 and then ch105.
Do you get sound from both of these points? (L and R)
If not try from pins 2&4 and 7&9 on pcm69

Also, check that the vias are still good. Might be worth putting a few strands of small wire through them and soldering from both sides. They can sometimes test good for continuity, but still cause problems, especially data and clock lines.

Any idea what was spilled on it?

[titusdis]

Dear SMDude!

So i took another go at it, took off all the resistors, and caps, and the op-amps as well. Cleaned the board again, and tried to remove that black juice.
Tried different mehods (alcohol, windex, etc...) no help.. finally i went with fine grit sandpaper. That did the trick.
Then i re-tinned the leads, and checked continuity as well (cheat pcb was above, so i could check what is damaged.)
I found an open lead, which should have been connected, but the corrosion damaged it. Unfortunately i had no time to finish, but it`s promising.
It`s R115 bottom pad. (power rail side) coming from CH109 cap. I attach some pictures as well.

This is not a spill, or a drink, but the juice from the SMD capacitors (i am suspecting the 0805 size ones) since,the corrosion is next to those caps always.
I am curious, since they leaked their insides, did i measure the correct capacitance? Hmm. will see. Anyways, i got new caps, new resistors, new op-amps today.
Not the same model of op-amps, but njm2115`s i hope they will do just as good. In case not, i have some lm833`s as well.

Thanks for helping me out with your opinions!
Please feel free to evaluate my smd work, i am really a beginner in this size. i take any hints, ideas with gratitude!

Cheers: Titus

[SMdude]

I'm not convinced that it is from the smd caps, well at least not the smd ceramic caps anyway.
I would be more going with some water or some conductive liquid made its way in and with power applied slowly started electroplating everything, corroding traces and solder and depositing elsewhere to make shorts/resistors where there should be none.
When this happens, the best way to clean up is with something mildly abrasive.
You have to clean the underside of all the components too, which you have now done.

Hopefully after fixing the trace and replacing the resistor, it will be good as gold again!

[titusdis]

IT`S ALIVEEEE!

Thanks for helping me out with your insights!
I fixed the trace, changed op-amps, and resistors-caps.
It`s working now, there is only one little issue left, which is after a piano sound shuts off, there is a little high freq noise-squeek for a 10th of a second, but only until the instrument `warms up`. so after 2 mins. it`s gone.
I haven`t changed the bypass cap at the pcm, and there is another smd ceramic cap at pin 19-20 of the pcm i haven`t  changed that either. Wonder what those filtering caps doing there. Hopefully 100 nF will do fine as c101 too.
i hope that will solve this. 
Titus