Digital piano won't power ON

[73's de Edd]

Sir Alektron . . . .et al . . .

Indeed, at the frequencies and fast and short pulses involved in that circuitry, that IK electrolytic, and having its ESR, would only be as effective as a 10 or 22 ufd cap.
Also, check the 10 ufd squirrely one out of circuit.
STRANGELY enough, Punysonic was derelict enough to have only used 85 deg temp rated capacitors for those 3 or 4 E-caps in that area, instead of a preferred 105 deg rating.
As far as the 6.3VDC cap rating, it's being only a decade scale down from the familiar 63VDC rating. As would a 630VDC rating that you would find for paper / poly capacitors now being sold for olde vacuum tube related repairs.

TYPICAL CAP ESR REFERENCE . . . .




73's de Edd
.....

 

[Alektron]

73's de Edd >>> "STRANGELY enough, Punysonic was derelict enough to have only used 85 deg temp rated capacitors for those 3 or 4 E-caps in that area, instead of a preferred 105 deg rating. "

Should I replace them with a new one, the ones I remove?

If that 10uF capacitor tests out fine, what are we going to do next, can I start putting back Q8 transitor, the 1000uF cap and the 10uF cap?

What is the game plan?

 

[Bluejets]

Did you get your 5v back yet?

If I change a flat tyre I usually don't worry too much if the engine oil is due for change.

 

[Tha fios agaibh]

73's de Edd >>> "STRANGELY enough, Punysonic was derelict enough to have only used 85 deg temp rated capacitors for those 3 or 4 E-caps in that area, instead of a preferred 105 deg rating. "

Should I replace them with a new one, the ones I remove?

If that 10uF capacitor tests out fine, what are we going to do next, can I start putting back Q8 transitor, the 1000uF cap and the 10uF cap?

What is the game plan?

Depends on how important it is and if your willing to spend a few $ on it or not.

Ideally, replace all caps with a higher voltage rating (provided they fit).
Or minimally, just replace and caps with low capacitance or high esr values. The call is yours.

I would just reinstall Q8 if it tests good.

 

[Tha fios agaibh]

If I change a flat tyre I usually don't worry too much if the engine oil is due for change.

No, but if you got a flat because a ball joint lead to its failure, it'd be wise to replace that too.

 

[Alektron]

Tha fios agaibh: >> " Depends on how important it is and if your willing to spend a few $ on it or not.

Ideally, replace all caps with a higher voltage rating (provided they fit).
Or minimally, just replace and caps with low capacitance or high esr values. The call is yours.

I would just reinstall Q8 if it tests good."

I have brand new capacitors in my arsenal, I would install new ones in place of those old capacitors that I take out of circuit, like the 1000uF and 10uF caps, the rest I would leave alone for now.

Q8 transistor I will reuse, since it tested out good.

 

[Bluejets]

No, but if you got a flat because a ball joint lead to its failure, it'd be wise to replace that too.

Not if the flat was caused by a whopping great nail.
Never seen a flat tyre caused by a crook ball joint.
You know full well by making a statement like that, you are simply nitpicking.

Point is, op found a shorted diode and as such I was curious as to whether or not the unit now has the 5v supply reinstated.
Surely there would have to be SOME indication that the op was on the right track without replacing capacitors all over the place.

 

[Alektron]

Blue Jet >>> " Not if the flat was caused by a whopping great nail. Never seen a flat tyre caused by a crook ball joint. You know full well by making a statement like that, you are simply nitpicking. Point is, op found a shorted diode and as such I was curious as to whether or not the unit now has the 5v supply reinstated."

Gentlemen ! there is no reason to jump at each others throat, that's not why we are here.

The 5 Volt is not back yet, we are working on it. If you look back at my posts you can see where we left off, and see what we accomplished so far, I included lots of detailed photos.

If I'll have the 5 volt I will post it. So far we are checking capacitors, and I ordered the diode that's gonna take 3 weeks to get it.

 

[Tha fios agaibh]

Not if the flat was caused by a whopping great nail.
Never seen a flat tyre caused by a crook ball joint.
You know full well by making a statement like that, you are simply nitpicking.

Point is, op found a shorted diode and as such I was curious as to whether or not the unit now has the 5v supply reinstated.
Surely there would have to be SOME indication that the op was on the right track without replacing capacitors all over the place.

Ahhh, we are trying to find the reason D23 failed. Capacitors being out of spec is a likely culprit. I'm not nit picking. I'm merely responding to your silly metaphor with one that matches. If you follow along, you would know that Alektron has not reassembled it yet. Their are many reasons that could lead to a failed diode or a flat tire for that matter.

Btw, this actually happed to me on the highway doing about 60mph.
A failed lower ball joint blew out my tire, and destroyed the rim and control arm.

 

[Alektron]

I was very curious about 73's de Edd's solder collection method. Is he still around?

 

[Alektron]

I guess I'll never find out the method of how to collect old solder .

Well, so be it;

I was thinking for a while now on this question:
" Why is that once the I-Flex connector is closed my voltage drops down at pin 12 and 13 from 49V DC to millivolts ? "



In my opinion, that Schotky Diode (D23) from the Main board, should NOT bring down the voltage that low, maybe some, but not down to millivolts, and with all those capacitors on the MAIN board checking out OK..
----> I didn't have an answer!




So I went back to look at the looney tunes cartoons, and see how power reaches pin 12 and 13 (on the I-Flex connector) on the power supply (yellow board). It takes a very simple route +VCC1, if you look at the schematic, it comes from one of the Giant Capacitors, then it goes thru two resistors (a ceramic type 2 Ohm 2 Watt ) and voilà, it reaches pin 12 and 13.

That is a simple route, it can NOT get any simpler than that, which means that the 49 volts DC should always be there closed or not closed with the I-Flex connector.


So I said to myself " let me take a peek at these resistors", and next I removed them out of circuit.
( I don't Mickey Mouse around anymore measuring components inside circuits, let's get serious ! )

So I removed these "bad boys" and sure enough one of them is OPEN, while the other one is reading 8.7 Ohms instead of 2 Ohms as it's posted on its side.



" Yes, yes, yes, this sounds wonderful !? Heureka !!! " I told to myself, but than I got a big question mark above my head.

How was it possible that I was getting a reading of 49 V DC at pins 12 and 13 with the I-Flex connector in the open position, if one of the 2 Ohms resistors was " OPEN" ?



Good question, huh ... mate?
Well, I think that the 2 Ohm 2 Watt resistor that was OPEN, it must've head a small connection under no load (a leaky one), but once under load with the I-Flex connector closed, it became (the resistor) OPEN due to its ill state.

What I think it led to the resistors failure is that the Schottky diode (D23) went bad at some point in time, and the 2 Ohm 2 Watt ceramic resistors started to over heat and failed.



I'm still waiting for the Schottky diode the new one, and for the ceramic resistors that I ordered recently. I'm not going to install two ---> 2 Ohm 2 Watt resistors. I'm going to install only one 4.7 Ohm 5 Watt ceramic resistor, that should be enough.

However; I don't know for sure if my hypothesis is correct, till all the parts arrive, get installed and the unit powers ON.

That is going to be the ----> Moment of Truth <---- Damen und Herren ! , zie time vil tell.

Please follow the additional photos, and danke schön for every ones help. Enjoy your weekend.

I'll be baack!

 

[Alec_t]

I'm not going to install two ---> 2 Ohm 2 Watt resistors. I'm going to install only one 4.7 Ohm 5 Watt ceramic resistor,

That will concentrate the heat in one board area instead of having it spread over two areas, so you may need to space it a bit further from the board than before, to avoid cooking the board.

 

[Alektron]

Alec_t : "That will concentrate the heat in one board area instead of having it spread over two areas, so you may need to space it a bit further from the board than before, to avoid cooking the board."

Space it you mean higher up from the board? Or extending the legs of the resistors for the whole length like in the photo?

 

[Alektron]

By the way, if someone can find me a place where they sell 2 Ω 2 Watt ceramic resistor I would really appreciate it. Seems like it's a little tricky to find this type.

Thank You.

 

[Alec_t]

Space it you mean higher up from the board?

Yes.

 

[Alektron]

Yes.

Ok, I'll do that, Thank YOU.

I wouldn't go that route to use a single 4.7 Ohm 5 Watt resistor, but I don't see 2 Ohm 2 Watt ceramic resistors for sale on the market.

Can I use a Metal Film Type resistor instead of ceramic that is a 2 Ω 2 Watt resistor? I found one of those for sale.

 

[Bluejets]

One way of getting a high voltage (when not connected) is having a bad connection somewhere, say a resistor gone high or a bad solder joint. Unloaded, you measure high, when current starts to flow it pulls the level low.
Can't think why your metal film resistor would not work.

 

[Alektron]

Still waiting for the Diode, the MA 738 by Technics. I received a Metal Film type resistor 2Ω 2 Watt, if that can go back instead of the Cement Ceramic type 2Ω 2Watt resistor then I will start putting them back on the PCB.


In the meantime before I put back the Q8 Transistor a (PNP type), I tested it with my DMM. Although it tested out OK with my ESR before. Q8 looks good.

 

[Tha fios agaibh]

I received a Metal Film type resistor 2Ω 2 Watt, if that can go back instead of the Cement Ceramic type 2Ω 2Watt resistor then I will start putting them back on the PCB.
View attachment 39951

What's the tolerance?
The old resistor was 5%.

 

[Alektron]

What's the tolerance?
The old resistor was 5%.

5 %