Digital piano won't power ON

[Alektron]

Thank you Mr. 73's de Edd for your help. So here is today's report .


" You might do a power down test and see if that diode (#13) is shorted, otherwise I think that they have made a mod on / for this ones +24VDC supply port source ."

I did test Diode #13 in the Power Down scenario , in diode testing mode on the DMM.




"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 took some new pictures, hopefully they will be more clear, if not let me know the area, and I'll do my best.

"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."

I think you are talking about this area.



I noticed there are two " Q9 " transistors, one on the MAIN board (green), and one on the other board (yellow). I mark their locations on the photo.





"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."

And here is the cherry on the cake. The left side Q9 also has Q4 next to it, and Q8 (although this is not on the drawing; however, nearby I found a 22uF 100V Capacitor (not a 22uF 63V, but I guess it is the cap we are looking for). Also nearby I found a 1000uF 6.3V capacitor.

Here is that DC voltage accross the 22uF 100VDC (22uF 63V) capacitor, with AC POWER ON.

198 mV



" 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. ) "

I tested D20; However I couldn't find D18, maybe you wanted to say a different number diode.



"If we have supply voltage from DDD and those diodes test good, and Q9 is conducting / creating pulses from its Collector to Emitter..."

What is the procedure for checking that Q9 (on the Main green board)? to see if it's conducting or creating pulses?I'm not really sure how to do that.

Last thing that I checked was the 22uF 100V Capacitor with my DMM's capacitor's testing mode (AC was Powered Down). DMM read 22uF. I also tested the 1000uF 6.3V capacitor DMM read OL. All the testing was done in circuit.

Is it really that simple that the 1000uF 6.3V cap is in the Open state?

 

[73's de Edd]

Sir Alektron . . . . .

I took some new pictures, hopefully they will be more clear, if not let me know the area, and I'll do my best.
MAGNIFICENT . . . . now my board viewing is not limited to just being a peephole area.
(But also strange, as at one instant I had seen the board mounted on a bamboo cutting board, but now I can't find that cluster of 5 photos.)
(I am referring to parts below by their schematic assignments, even though some seem to be having different assignments on the PCB proper.)

BUT that is certainly looking like the expected parts that we are needing to find, with the real clincher being the landmark L2 toroid . . .ringing inductor . . . . and its D18 rectifier diode and the main 5V storage capacitor, being the C63 1000@6VDC electrolytic.
But it seems that we are missing the required + Vcc supply voltage on the + lead of the C50 electrolytic.
That should be fed in from the other main power supply and there may be a popped circuit protector on that line.
Notice that on C50 caps + lead, that it has common node connections being made to:
R50
R83
D12
Q2 Collector
Q8 Emitter of the Q9 2SB946P power transistor

And the may be or may not be anode lead of the D14 diode to the possible + 24VC supply circuitry

Now in confirming the foil paths to each of those parts . . .can you ALSO find the foil path that is carrying that +VCC supply into this circuitry ?
In order to then back track its wiring path, and see EXACTLY how that is being routed back into the other power supply ?

Also I am not seeing IC17 nearby.

73's de Edd

 

[Alektron]

I am looking at this thing but I cannot find those R50 and R83 resistors, I am having some difficulty tracing things on these boards.
I took some picture, I am showing where those picture were taken. Please de Edd go over them, see if you can see what we are looking for. I'll do the same. If more photo's needed, let me know.

Here we go:

 

[Alektron]

I flipped over the bottom portion of the Main Board view for easier comparison between TOP and BOTTOM views.

 

[Alektron]

Photos to trace the flow from Main board to the other board. Note some photos are flipped horizontally.

 

[Alektron]

Some better pictures of the board with the two giant capacitors (top and bottom).

 

[Bluejets]

I've been following this post and right back in the beginning, output of the transformer on the drawing shows 20v ac and yet the Op shows 38v ac.
Also his dc voltage readings on D3 (D5 by the way is the same place) is 56 v dc. Way to high.
Just wondering if someone hasn't played with the input voltage circuit area e.g. selector switch or the wiring to same.

Alektron, seems you are getting confused ...........for example Q9.(similar for other devices also)
It is usual for all the power conversion to be done on the one board.
You look for Q9 on the green board and circle a transistor there but spec sheet for the one Edd is referring to shows it is the same case outline as Q2 on the big heatsink. I think Edd actually pointed this out.

Edd, just wondering if the 5v section is actually shutting down as a result of this higher than expected voltage.

 

[Alektron]

Main board has a marking of 36V on it. With this model there might've been some changes.

 

[Bluejets]

Granted however it does not seem practical to supply 56v to ground just to generate 24v and 5v .
36v you show could be taken from across converted A-B output in a 28v output.(ie Vcc+ and Vcc-)

Very strange how you get double output (56v) to ground which is what one would expect across Vcc+ and Vcc-.

Thing is you have the convienience of having the board your end but we cannot see actually what you are measuring and how.
Bit of a problem there I think.
Anyhow I'll leave it to Edd.

 

[73's de Edd]

SIr Alektron . . . . .

Lots of parts have different numbering assignments, comparing schematic and actual board but . . . . . the +5VDC Dee Switch Mode power supply section ground zero is being within your RED OVAL of photo #39069. ( Being content, within your post # 41 . )

You have a Flex-i-Connector that is labeled CN2 on the POWER supply board side and its other half connects to the MAIN board, and is reidentified as being CN12 over there.

Our main supply voltage is supposed to have its origin on the PS board and has to pass thru two circuit protectors IP3, IP7 and I Pee Freely, before it routes to the same combined Pins 12 and 13 of CN2 side and flows over to the identical Pins 12 and 13 of CN12.
Power up and see if there is our unknown voltage at pins 12 and 13 of CN2, if not check to see if IP3, IP7 are open.

If our ? level of voltage is there, I next need to see why it is not getting over to either the + of that 22 ufd electrolytic or its same-same connection, being the Emitter of our actual renumbered "Q8" switching transistor .

73's de Edd

 

[Alektron]

" the +5VDC Dee Switch Mode power supply section ground zero is being within your RED OVAL of photo #39069. ( Being content, within your post # 41 . )"

Where is the number 39069 displayed for that RED OVAL photo? I am looking all over post #41, but I don't see it. I'd like to make sure I'm on the same page (I mean photo) with you . Or just Save it and Re-Post it.

I'm going to reconnect the Power Supply board and the MAIN board thru the Flex-I Connector, to take our measurement at Pin 12 and 13.

" IP3, IP7 and I Pee Freely " hahaha.

Do I have to reconnect the connectors on the periphery of the two boards in order to take the measurements ?(marked with yellow oval circles)

One more thing, when I take the measurement at Pin 12 and 13, you want me to go with the RED lead of my DMM to pin 12 and 13, and the black lead to the Ground wire that comes out between the two giant Capacitors, right?

 

[Alektron]

Here are the measurements, with everything installed and connected like in the first photo
(no connections omitted).

Please follow the pictures.

It seems like we are getting a low voltage at the 12 and 13 pins (188 mV); however, once disconnected I'm getting a pretty high DC voltage of 49 V (at both 12 and 13 pins)

I checked the IP7 and IP3 circuit protectors with my DMM's continuity check, there was a buzzing, meaning they are good.

Seems like only the +15 V and -15 V stays in both scenarios (open and closed I-Flex conn.)

I wonder what happens when the I-Flex connector is closed, where is the electricity going?

Kind of like, where does the light go once the switch is turned off in the kitchen? ans: ( it goes into the fridge)


End of Report

 

[73's de Edd]

Sir Alektron . . . . .

Scanning 25 pages of schematics . . .all condensed down to this now most relevant info . . .
It's marked up so that I can relate down to the most minute circuitry action if so required.

INITIALLY though, it looks like we have confirmed the +VCC voltage making it from the power supply up to the Flex-i-connector and that is where the voltage is being pulled down to hundreds of millivolts if its connection is made back to the power supply via the pins 12 and 13.
Some of the +5VDC Bee voltage supply is being used on the main board where it is being generated, while some of it passes thru Circuit protector IP1 and feeds to other circuitry associated with the output at the CN2 5 pin connector and its Pin #1.
I don't think that this will be it , but the first test would be to power up the system and confirm the Pin 12 and 13 voltage is still pulled down, then you unplug CN2 to see if the voltage comes up.If no luck, then let's look at the mark ups.
The +VCC enters at the CN12 pins 12-13 and follows the RED ARROW path, at each node where it meets a component, I have designated a RED or GREEN SQUARE .
A RED SQUARE path indicates where a bad component could cause a pull down of the voltage.
A GREEN SQUARE path indicates where circuitry on down that path would not be pulling the voltage down as severely as is being done.

Testing below will be done with no AC power on the unit . . .

The next test to do would be to place DMM metering in its OHMs function at its LOW ohms range and short your meter leads together to confirm what a low ohm or short reading displays as.
Black meter probe to your usual ground point and the RED lead to the Emitter lead of the newly assigned RED Q8 transistor, to see if this supply circuitry coming in from the CN12 is anywhere near being grounded out.

If getting a low ohmmic reading, move to the Collector of Q8 to see if a low reading is also being there.
If low readings on both sides of Q8, then lift the OHMS lead probes and test between Q8 Collector to Emitter to see if it has crunched and shorted from its Collector to Emitter. Reverse the polarity of the leads an retest again, expecting the same low reading for a shorted Q8.

Awaiting your findings . . . .

Next tests will be to see if D18 switching diode or D20 6.2 volt sacrificial Zener diode is shorted.
OR . . . if the YELLOW +5VDC Dee supply from the J test point is being pulled down by circuitry tied into it, on this same MAIN board.

REFERENCE SCHEMATIC SNIPPET . . . . .



73's de Edd

 

[Alektron]

I just found some new cartoons , these might be even more true for this model...

The quality is not the best, but I can definitely see Q8 listed as Q8 on it, also there is the +36V displayed, and I marked the Green and Red squares on one of the new schematics...

 

[73's de Edd]

Sir Alektron . . . . .

HEY ! . . . . where did you get the new cartoons ? . . .Disney . . .or Looney Toons ?
Give me a link to their stored site / access. So I can be using the proper assigned numerical designations, when referring to a part in the future.

To date . . . . I had only corrected the Q8 and IC34 numbering differences . . . in RED..

But the IC34 only has an A and a B section, whereas, up on the left center inset they were designating the + and _ supply inputs to the IC and they erroneously designated it as IC34C.

73's de Edd

 

[Bluejets]

Transformer still shows 20v centre tap.
Images a bit blurry though.

 

[Alektron]

Bluejets: "Transformer still shows 20v centre tap"

Isn't that weird? I thought about that myself, but who knows if there is an actual schematic out there that would resemble our reality of what we've got in here.


73's de Edd: "HEY ! . . . . where did you get the new cartoons ? . . .Disney . . .or Looney Toons ?
Give me a link to their stored site / access. So I can be using the proper assigned numerical designations, when referring to a part in the future."

Wish I could give you a link. Someone shared it with me via e-mail, reassuring me that they are for my digital piano, but who knows what's the truth anymore? ( if you have an e-mail address I'll send it to you )

For example: I cannot find (according to the new cartoon) a Diode #24 on the Main board (either on top or bottom of the board), which would be Diode #20 on your schematic. Although I did find Diode #23, hiding on the bottom of the Main Board right under the L2 inductor coil.


73's de Edd: "To date . . . . I had only corrected the Q8 and IC34 numbering differences . . . in RED.."

No harm done, anything you do Edd, is simply getting us closer to a successful finish. Do as many corrections as you would like, I am only the assistant, you are the doctor! Without your help this piano would probably stay silent forever.

Truth is, I never heard this piano before, I inherited it in its silent state, but when we succeed I'll post a video so we can all hear its magnificent sound.

Ok, enough said, here is what I did today, please follow these pictures, they worth more then a thousand words... (wish dollars)

 

[Alektron]

This is where Diode #23 is hiding, right underneath that L2 toroid coil, but where is Diode #24?

I see Diode #20 though, that one does appear on Edd's schematic, on the picture you can see it under Q9.

 

[Alektron]

So...the D23 from the new schematic and D18 from the "old schematic" , they both designate an MA738 diode, or more precisely a Schottky Barrier Diode MA2Q738 (aka) (MA738) by Panasonic. A Silicon Epitaxial Planar type for high frequency rectification. You can read more here, if you'd like:
http://html.alldatasheet.com/html-pdf/101991/PANASONIC/MA738/484/1/MA738.html

Question is how should I test this "Bad Boy" since he dwells on the bottom of the Main board?



Now for the D24 (old D20), I'm not sure how does that look like.

According to the datasheet for an MA2062 (1F), color code should be Blue Red Red for a 5.8V min and 6.6V max Zener diode, but I do not see anything like that on this Main board.

Here is the datasheet for an MA2062 Zener Diode:
http://www.datasheetspdf.com/pdf/545899/PanasonicSemiconductor/MA2062/1

 

[Alektron]

I was able to finally locate Diode #24 on the Main Board.

Like the spec sheet says, the MA2062 (1F) does have a BLUE RED RED band on it. I also found the 470uF 6.3V capacitor.

I used these two components for testing the H and I points from the schematic, trying to see if I can get the +5D showing up, but all I got was 650 mV at both component .

Please follow the pictures.