Digital piano won't power ON

[73's de Edd]

Sir Alektron . . . .

Isn't it great to have so ma a a a ny choices . . . now, just take yer' pick.
( HINT . . . . use same-same- or the 2nd-3rd or 14th down wire leaded radial units )

https://www.mouser.com/Passive-Comp...apacitors/_/N-5x76s?P=1yztzayZ1yo19p6Z1z0z7l5

SOLDERING . . . .
MY own preferred and highly effective modus'es operandi-muss-ess-es . . . . .
For the pulling or installation of a problematic component.. . . .

Pulling:

Orient the chassis / board so that the 2 tips of the installed capacitor are pointing straight up and that the board is level to the bench. That orientation will then let you place a dot of rosin flux onto each of the existing solder joints and feed in fresh 60/40 solder, until you achieve a much larger molten solder mass of each, with them being about the size of a 3/16 ths of an inch ball at each joint.
When those solder masses have been achieved, surfactal tension will hold the balls centered upon the pins.
You then start rapidly moving the soldering iron tip between the two molten solder masses. This leaves the free hand to move to the bottom side of the board and exert "micro" wiggles upon the component. At the proper amassed heat level the component will be felt to loosen and it can then be pulled straight downward to release from the board.
If you have either a multi level board or a terminal / ground plane that is laterally sapping heat away, you will eventually reach that heat threshold, where the part will loosen free from its solder bond.
In that manner, you only have only had to come up to that heat threshold, and thereby not having subjected the immediate mass of the board to any excessive heating.
Any failure to quickly achieve that could be blamed upon trying to use too low of a wattage of soldering iron.
A 50 or 60 watt iron, wherein you get in and out in a hurry, just about always works, whereas a 40 or less wattage of iron might not be able to deliver the required heat threshold.
You also want to use a well and continuously tinned iron tip.

INSTALL:

You have the now cooled solder balls at the connection holes. You get either a bamboo skewer with its sharpened end OR you can replicate that shape with an aluminum or stainless rod or from hardwood dowel stock. Since that solder won't stick to them.
Prep the new component by rosin flux coating of its terminals and then do a solder tinning its terminal/ lead.
You heat up one solder ball to its just molten state and insert just enough of the bamboo skewer from the bottom such that you will have left a dimple in the solder present at the bottom of the board.
Repeat for the other solder ball and its foil land.
You now have two dimples that you can "FEEL" for, with the end tips of your new component, to then position themselves down within the two cavities..
TIME to triple check the polarity of the SUUUUPER cap on its + to - terminals to be that they are going into the proper holes.
Place the board / chassis in the same positioning that the component was being in when pulled.
Place dots of rosin flux upon the solder balls and then start the same fast back and forth movement of the soldering iron tip between them until they both become molten.
Then you place the components lead tips resting within the earlier created solder divots, and being constantly pressed towards the board, the component should eventually move fully down within its mount holes at the lowest applied heat threshold .
Then you move to the top of the board and slope the board / chassis 45 degrees to heat a solder ball and drain off the excess solder to your irons tip, leaving the residual solder at that perfect " not too much-not too little " amount. Move to the other solder ball and do the same.
Move the board / chassis back to a level position and place a drop of rosin flux on the ball and heat and watch that mystical / magical flux, then fully enhance the solder flow and leave a perfectly re flowed solder joint.

Thassssssssssit . . . . .

73's de Edd

 

[Alektron]

Thank you Mr. 73's de Edd >>>>> Soldering is an ART.

I was able to re solder the Super Capacitor back into it's place. (see photos).

One thing I noticed as I was checking the continuity between the Super Capacitor's legs and the PCB (after the soldering was done), was that the Super CAP had continuity in both direction. In one direction continuity was always there (between + and - ), in the other direction continuity stopped after a while. Is this because the DMM charges the S. Cap while testing it?

I did not reassemble the Main Board into the Piano yet, I will soon.

 

[Alektron]

The solder on the Main PCB is a hard solder with a high melting point. Due to its hardness, it's probably also brittle and more prone to micro cracks.

 

[73's de Edd]

Sir Alektron . . . .


the Super CAP had continuity in both direction. In one direction continuity was always there (between + and - ), in the other direction continuity stopped after a while.

In one manner, where you had the ohmmeters polarity being connected backwards the cap showed leakage or conduction by virtue of the wrong polarity being applied to the caps leads.
When you reversed the leads the + voltage of the ohmmeter matched up with the capacitors + lead and after a time the capacitor then started taking on a charge and the reading declined.

Here is that units POWER SUPPLY CIRCUITRY all amassed together as a compact unitized schematic.

It originates at the power transformer at top left and flows to the right and there are SEVERAL marked points to check due to the great number of circuit protectors used.

THe DDD +VCC goes down to the bottom left where it is marked up again as DDD and is processed down to a +24 VDC supply and a +5 VDC which exits at JJ at Jack CN2.
It also passes as JJ at CN2 after, first passing thru a circuit protector.

ORGANS UNIFIED POWER SUPPLY SCHEMATIC . . .

73's de Edd

 

[Alektron]

I was able to locate CN1 and CN2.

Unfortunately my expertise in checking those points that you mentioned on the schematic, is very limited.

Unless you are willing to guide me thru, what exactly I should be doing, in small steps...

 

[Alektron]

I reassembled everything and the same old same old is happening, only the RED LED is ON, nothing else comes to life.
I checked the voltages again at the connector between Main PCB and the other PCB, instead of getting 25V ( two places) , now I'm getting 31V DC. But once the connector is put into place by connecting the two PCB's the voltage at the 34V DC drops down to less than 1V.
Voltage across Super Capacitor is 900mV.

I also checked if there is a 5V output at the CN2 and CN1 connectors, there is none.

 

[Alektron]

I'm not sure if this is the correct way to check.

I tried to test "point A" involving the D3 and D5 diodes. Using the DMM I got a reading of 52.6V DC and a 115V AC(only in one direction). With point "B" I get the same results.

Is this the right way? I'm not sure what should I use as a ground.

I don't understand why am I seeing 115V AC, when the input is 38V AC.

Also, the "cartoon" is showing that there should be a 20V AC comming in, I'm getting 38V AC on my DMM.

"Houston, we've got a problem"

 

[73's de Edd]

Sir Alektron . . . . .

Relevant to your lower AC voltages from the power transformer secondary windings, if they are reading high that could be indicative of some connector is not plugged in, so that a portion of the loading of the supply transformer is not there, so the voltage would be high until that section is properly loading down the supply and pulling the supply voltage on down to a normal value.

I need a more specific connector identification . . . relevant to the . . .
But once the connector is put into place by connecting the two PCB's the voltage at the 34V DC drops down to less than 1V.
Lets ignore AC readings for the present and your meter negative ground connection will be the common center junction of the C2 and C3 main filter capacitors. That is being half way between YELLOW A and B test points.
We will be doing mostly + DC voltage readings, with a few B-C-F and H negative voltage readings.

You say
But once the connector is put into place by connecting the two PCB's the voltage at the 34V DC drops down to less than 1V.
WHAT CONNECTOR ? AND IS THAT possibly being TEST POINT A-D-G or E ?

Voltage across Super Capacitor is 900mV.
Yo nevah gonna see that come up, until the 5VDC supply is active.

If you can get the initial A-H readings that would have voltages from all test points, and a need to move to the small supply for the 5VDC and the minor +24 supply at the bottom left of the schematic / cartoon.

If you get something in the order of that 1VDC reading (Where?), we need to power down and move to ohmmeter function readings to see if we have a shorted semiconductor (s).


73's de Edd

 

[Alektron]

Primary winding gets 125V AC from the wall outlet.

I get 78V AC in the secondary winding (half of that is 39V AC instead of 20V like the schematic says). Everything is plugged, no connectors hanging in the air.

I was only able to check the point A and point B (to ground), I got a DC reading of 52.8V.


For the other points E, G, F, H. >>> I have no clue how to find them, I would need help with that.


For the 34V, I included a photo. This connector is located between the Main Board and the other PCB board with the two giant Capacitors.

When the connector is in place instead of the 34V I get a reading of 1.3V DC, but this might be irrelevant.

 

[Alektron]

I was able to check point E and F. See photos for how I came up with the -15.2V for point F and +15.2V for point E.

What is the IP5 and IP6 symbol on the schematic (looks like a VHS tape).

 

[73's de Edd]

Sir Alektron . . . . . .

I believe that after reading your RED LINED connector info, that we can assume that your +15 and -15V supplies are being good, and now you can track the component trail from A up and to the right to DDD.

I might equally assume that your voltage drop situation of 34V down to 1.3 is one of the two lines that I show as feeding to a LED. When you complete a circuit continuity with it via a plug / connector the voltage drops . . .as it should . . . since that line was previously being totally unloaded.

ICP's are Current Protectors / fuses and you will have to identify its / their physical appearance by finding one by its symbolization assignment that is being silk screened next to it on the PCB, I remember 3 different casing profile variations being used thru a 40 year span of years.
Once you confirm voltage at DDD, then move to the PCB that has the two power supply voltages that I have shown in the lower left inset schematic.
There you will see how the same DDD is being connected in there and it primarily feeds to the right to Q9 power transistor.

73's de Edd

 

[Alektron]

First of all I would like to thank you for all your help Mr. 73's de Edd, thank you so much.

Second: I was able to check Point H and G. Here is how I found those points. I was able to locate IP5 and IP6 circuit protectors, it actually says right on the PCB IP5 and IP6. Found the two CAPS one 100uF 16V, the other was 10uF 16V. I guess I could've also used those +15A and -15A points? (please see the photos)

 

[Alektron]

Moving on to the next Point to check >>>> + VCC D D D >>> TOP of the Schematic !

I located the two Circuit Protectors >> IP3 and IP7, also found L1 and L2 (are these inductors?). I saw a big red component, underneath it had a capacitor symbol, I couldn't read what it said on the side, on the photo I marked this component with 3 yellow question marks. I would assume that's the Capacitor #4 TF 1.5.

I noticed that +V "thru hole" I put my test lead there. See photo, that's how I got a reading of 52.6V DC for DDD.

Quote:
"Once you confirm voltage at DDD, then move to the PCB that has the two power supply voltages that I have shown in the lower left inset schematic.
There you will see how the same DDD is being connected in there and it primarily feeds to the right to Q9 power transistor."

This is what I'm going to do next.

 

[Alektron]

Here is the schematic for that +24V and +5D, I broke it up into a separate segment.

 

[Alektron]

I was able to locate point JJ for the +5D at Diode #20. I got a reading of -227mV.

For point " I " I couldn't do any testing, since Diode #19 is totally missing from the PCB. I took a measurement from Diode #13 it was like 500 mV.

 

[(*steve*)]

The lack of that component (and the associated lack of components near it) suggests that for your model of the digital piano, a part of the power supply is not required (perhaps it supplies a voltage rail that is unused?).

 

[Alektron]

I'm not sure Steve. I really hope I'm doing things the right way. That's why I document every step of the way, just to make sure I'm not checking something the wrong way. I'd really like this piano to work again, it is one of a kind.

Although I'm a Roland guy, Technics was always couple of notches above the others, and very user friendly.

Too bad Panasonic shut down the digital piano and electric organ section, and they only resurrected the turntable.

I'm waiting for the Doctor to come in

 

[Bluejets]

Some of those readings you give are way off, bit like you are not measuring correctly. Are you sure you have a ground connection and you are on the right meter scale?

 

[Alektron]

I use the ground connection which is a black wire that comes out between those two giant capacitors and it is fastened to the board with a screw.

You can see the ground cable in this photo.

 

[73's de Edd]

Sir Alektron . . .

For point " I " I couldn't do any testing, since Diode #19 is totally missing from the PCB. I took a measurement from Diode #13 it was like 500 mV.

There must have been a production change, as this is a minor supply, as it starts, at the left, it is taking its initial power with steering diode D14 from our DDD supply point then to the right thru additional diode D15, then gets some filtering / isolation from C69 then passes thru the 2.2K resistor and the D13 zener diode which is supposed to initially regulate down to a 27VDC level.
Now if the previously described parts are installed and DDD is powered up and only 500 mV is at the D13 cathode at the top . . . . it could possibly be suspect of being crunched.
HOWEVER the physical size of D13, which I am seeing is only a 500-700 mw power rated unit, I would suspect that position to be minimally be incorporating a 1W or + rated Zener diode.
You might do a power down test and see if that diode is shorted, otherwise I think that they have made a mod on / for this ones +24VDC supply port source .

I was able to locate point JJ for the +5D at Diode #20. I got a reading of -227mV.


I have two phantom board views of that small, dual portion power supply that we are looking, but they are totally displaying as black and white, with no intermediate shades of gray, for definition, so I can't find any landmark parts of that circuitry to tell you where to look for it..

I will say that, this circuitry should be built as a parts island , within an internal portion of the MAIN A board.
I think that at one time I saw its all important main Q9 switching transistor which should be in the casing profile of the Q2 and Q4 power transistors which you can see in the #35 photo just above.
Then I lost view and that location of that transistor on the phantom photo..

Since it is creating the major +5V Dee power supply for the unit, I feel that with its current demands that it will justify a heat sinking, so seek out those transistors provided that type of treatment first.

Then, being tied to Q9 emitter, will be the magical electrolytic, C50 . . . a 22 ufd at 63VDC rating . . . . of which its negative lead will be your metering ground referencing and the + lead will be the DDD supply source input which we had been looking for.
Give us that DC voltage level, that we are deriving our power from, for the 5VDC Dee supply.

However, since you have found output from the +5VDC Dee supply . . . . at JJ . . . to be down to a mere -227mV,
In a no AC power connected condition, test to see if either of your D18 switching or D20 6.2 V Zener diodes have failed, by the testing of their junctions, with your meter being placed in its diode test mode with meter leads swapped in polarity to make a two part test.( BUT 227mV does suggest a non shorted D20 and a good . . .non shorted junction on D18. )
The 227mv reading is indicative of a good junction reading on a Schottky family of rectifier diode . . . like D18.

If we have supply voltage from DDD and those diodes test good, and Q9 is conducting / creating pulses from its Collector to Emitter, this power supply problems solution just might be as simple as replacing C63 . . .1000ufd @6V electrolytic which has had its brains and internals ABSOLUTELY TOTALLY 99 and 69/70ths % HAMMERED out, by the heavy pulse actions it has been subject to through its operating life . . . to date.

FIO . . .
I see that your IP . . circuit protectors . . . are being in the same profile case that I initially found them to be originating in, 38 years ago.
Other than their IP markings and numbers, they would pass as a TO-92 plastic transistor case, BUT with it having only 2 leads.
Some . . . voltage variable . . .Varactor diodes get the same casing treatment.



Seek and ye shall find . . . . .

73's de Edd