Digital piano won't power ON

[73's de Edd]

Sir Alektron . . . .et al . . .

Why not figure out where you are going to source the new diode from and check their solder offerings and we can comment upon the possibilities that they offer.

It's absolutely normal for me to scavenge 70-80's vintage " free " electronics boards to harvest components AND also use downward gravity to to get ALL their solder and tap on the lid of a small jar with a 1 inch hole in it.
Water is in the glass and the small solder drops form on the way down. With time, I must have accumulated 12 of the largest orange pill containers, crammed full with them. . . . them being a bit weighty also.
Just pick one droplet of the size needed for your joint and then have a drop of liquid rosin flux and a Stainless Steel tweezer set applies the solder drop in place and then you solder . . . . all for FREE.
( My flux even comes from my pine trees sap + denatured alcohol used as its solvent.)

I have mostly used ?(Brain fart) and their inner "44" rosin core or Ersin Multicore solder, and of a sizing either 1 or two gauges down smaller in size from what you showed us. 60 tin 40 lead or sometimes PWICEY PWEMIUM BWEWED 67/33 blend . . . . . with even a bit of silver bearing stashed away.

FAILURE ANALYSIS . . .
As it was , with that +VCC being pulled down, and you not finding Q8 dead shorted from C-E, and a 22 ohm resistance presence was being found on our +5VDC Bee supply line.
I just needed Q8 completely out of circuit to be sure that the unit was not avalanching from C-E and acting like a power zener after it had a voltage presence upon it.
With it out of circuit . . . . then the circuitry to he left of Q8 and the right of Q8 was isolated . . .and the problem was being on the right half of it.
HOWEVER, I wasn't expecting a 22 ohm reading of the diode, usually they either open circuit or dead short.
THAT then accounted for the 22 ohms as then NOT being a load on the +5VDC Bee supply line as I was suspecting, which could only account for an ~ 250 ma loading on the supply .
BUT with no diode there it could not rectify the ringing of the toroid inductor and collect its energy in the 1000ufd /6v storage / filtering capacitor.

Didn't know that you had the ESR + meter . . . . usually I am having to work with people that are so piss pot poor . . . .equipment wise . . . . that we have to find innovative / cutting edge work arounds with Scotch tape , toothpicks and split clarinet reeds . . . . along with a liberal sprinkling of flooby dust.

How about a testing of those 4 E caps between the Super cap and the toroid area. Most of my suspicion is directed at the 1000 unit as it could have been instrumental in the diode failure, by gradual time driven overheating of the diode. ( And that might account for the diodes abnormal failure mode.)

Looks like that KLEIN that you now have is fully encroaching upon being a FLUKE wannabe.

73's de Edd
.....

 

[Tha fios agaibh]

Thanks 73's de Edd, but could you elaborate on what exactly in the 1000unit you suspect might have precipitated this failure?

I'm wondering if the over voltages Bluejets commented on could be a reason. Specifically, the transformer feeding cn1 (should be + and - 20v) was much higher.
Could this higher voltage have caused a thermal runaway condition in D23?

 

[Alektron]

"Tha fios agaibh " >>> Good old-fashioned toxic lead solder.

I'll order it today. Thank you for the link.


" It will do, but honestly your better off with one really good meter than 25 mediocre meters.
Save up and buy yourself a Fluke and or a Simpson. You won't regret it. "

I only bought that analog meter just so I can have something that is analog. I'm not gonna use it for any accurate testing. Probably I'll use it with my breadboard electronic experiments.

No doubt Fluke is a very good DMM, but if we compare them and let's say that Fluke is the Bentley of electronics, than Klein is definitely a Mercedes. This Klein 600 MM has a pretty good reputation when it comes to accuracy and reliability.

 

[Alektron]

Tha fios agaibh >>> " Thanks 73's de Edd, but could you elaborate on what exactly in the 1000unit you suspect might have precipitated this failure? "

I think 73's de Edd is talking about the 1000uF Capacitor, see photo, it's located next to our Q8 transistor.

 

[Tha fios agaibh]

Tha fios agaibh >>> " Thanks 73's de Edd, ....I think 73's de Edd is talking about the 1000uF Capacitor, see photo, it's located next to our Q8 transistor.

Ah thanks. I was thinking the upstream board left of Q8 was called 1000unit or something.
I could still use some clarification of how it would impact the diode. I'm thinking maybe the absence of sufficient capacitance caused the inductor to spike back to the diode instead or resonating through the lc circuit?

 

[Alektron]

73's de Edd >>> " Why not figure out where you are going to source the new diode from and check their solder offerings and we can comment upon the possibilities that they offer. "

Well I was hoping that you could point me in the right direction where to find this Diode #23 ( MA 738 ) on the market.

_________________________________________________________________________________________________________
" It's absolutely normal for me to scavenge 70-80's vintage " free " electronics boards to harvest components"
I understood your sentence up to this point that you harvest components, but from here you lost me...

" AND also use downward gravity to to get ALL their solder and tap on the lid of a small jar with a 1 inch hole in it."
Do you use a Heat Gun or a Soldering Iron? I mean I have a hard time picturing this. I understand the small jar with a lid that has an opening of 1 inch in diameter, but downward gravity??? Would you please take a picture of this procedure, I am very curious to learn this, but it's not very clear to me.

" Water is in the glass and the small solder drops form on the way down."
I'd like to see this process...
_________________________________________________________________________________________________________
" just needed Q8 completely out of circuit to be sure that the unit was not avalanching from C-E and acting like a power zener after it had a voltage presence upon it. "

Thank you for explaining this, now I know why Q8 was removed. Can I reuse the old Q8?

" Didn't know that you had the ESR + meter . . . . usually I am having to work with people that are so piss pot poor . . . .equipment wise . . . . that we have to find innovative / cutting edge work arounds with Scotch tape , toothpicks and split clarinet reeds . . . . along with a liberal sprinkling of flooby dust."

I ain't no Mickey Mousing around here .

"How about a testing of those 4 E caps between the Super cap and the toroid area. Most of my suspicion is directed at the 1000 unit as it could have been instrumental in the diode failure, by gradual time driven overheating of the diode. ( And that might account for the diodes abnormal failure mode.)"

Should I remove those 4 E caps that you mentioned out of the circuit for testing ?

" Looks like that KLEIN that you now have is fully encroaching upon being a FLUKE wannabe. "

I like it, it's a pretty good DMM.

 

[Tha fios agaibh]

Here's a source but I'd wait to order until you know all the components you may need.

https://www.digikey.com/product-det...-components/MA2Q73800L/MA2Q73800LCT-ND/267207

 

[Alektron]

Thank you for the link. Why does it say " Part Status >>> obsolete"?

 

[Tha fios agaibh]

I don't know I just googled it.
Try Mouser. They are also a good source.

You can usually esr test caps in circuit but I like to pull them and also check with a capacitance meter.

 

[Alektron]

I checked those 4 capacitors that 73's de Edd instructed me, that are located between the Super Capacitor and the L2 toroid coil.

Please see the following pictures. I'm starting with a reference photo so everyone can be on the same page with us.

I had to remove the 1000uF 6.3V capacitor from the circuit. In circuit, my DMM was reading < OL > while testing the 1000uF 6.3V capacitor. Once removed from the circuit, I got some numbers. (see photos)

I checked those other 3 remaining capacitors in circuit, however, one of the 10uf 16V capacitors did not show an accurate reading, with my DMM, I was getting 196 uF (instead of 10 uf), my ESR just simply looked at it as a DIODE.

I'm not sure if I should remove this 10uF 16V capacitor out of circuit or not ?!

I was really hoping to see this 1000 uF shorted or open, but I don't see that... Let's see what the Doctor says...

 

[Tha fios agaibh]

When in doubt, pull them out.
It's seeing it as a diode because theres one parallel to it.

I got to say though, I'm confused by the specialty voltage rating of 6.3v. I've never heard/seen such thing.
Usually their rated at 10v, 16v, 25v....etc.

It appears your 1000uf cap is fine.

 

[Alektron]

6.3 V is very common with 80's and 90's Japanese keyboards and digital pianos.

I just ordered two MA738 diodes for $12 with shipping. It will take me a while to get it though.

Here is the place I got it from...
http://www.pacparts.com/part.cfm?part_no=MA738&mfg=Technics

This seems like it's an original genuine part made by Technics, aka Panasonic, or even more precisely Matsushita Electric Industrial Co., Ltd. .

I ordered 2 diodes just to be on the safe side of things.

 

[Tha fios agaibh]

6.3 V is very common with 80's and 90's Japanese keyboards..

Maybe so, but why?

Why wouldn't circuit designers just go with a 10v standard voltage rating?

 

[Alektron]

I'm not sure why, but that's what I've seen... I'm sure there is a mathematically justified answer to that, since why would be 6.3V why not a round number, or 6.5? Maybe it makes this capacitor a safety device by limiting the voltage it can handle, and 6.3 is a magical number. Honestly I don't know.

I'm sure 73's de Edd will be able to answer that question.

And since we are at the subject, should I replace that 1000uf 6.3V Capacitor, with a new one? and if the new one is 16V would that be OK? I know higher voltage is OK, but in our situation, would that be OK to have a 16V going back?

 

[Bluejets]

Maybe so, but why?

Why wouldn't circuit designers just go with a 10v standard voltage rating?

Smaller physical size.

 

[Tha fios agaibh]

Smaller physical size.

Yes, but there's got to more to the precise rating. 5 or 6v, I can see. But 6.3v?

Perhaps they are high precision at that voltage?

Do they have other non-standard ratings like 16.3v or 25.6v?

 

[Alektron]

"Waiting for Cousteau" . . . aka >>> 73's de Edd, the explorer and researcher of the electronic realm ... I'm curious how that solder harvesting is done...

 

[Tha fios agaibh]

You need to pull the 10uf cap that reads 196uf and test it out of circuit. Everything else looks ok to me, including the transistor you thought you fried.

 

[Alektron]

" Tha fios agaibh>>> You need to pull the 10uf cap that reads 196uf and test it out of circuit. Everything else looks ok to me, including the transistor you thought you fried. "

OK.

 

[Tha fios agaibh]

You need to pull the 10uf cap that reads 196uf and test it out of circuit. Everything else looks ok to me, including the transistor you thought you fried.

On second thought, some of those esr readings are a bit high.