Digital piano won't power ON

[bushtech]

It's easier to test a schottky with an analogue MM. Have you got one?

 

[bushtech]

If you have set it to X10. Put probes on, check reading, swop probes, check reading. One way you should get full deflection, other way you should get some deflection. If so schottky probably OK

 

[Tha fios agaibh]

After my readings on Diode #23 in Diode Testing Mode on DMM, ( forward and reverse ) I got a 20 mV reading. Could this be in parallel with something else? or I do have to remove it in order to test it properly?

I guess you missed my last post.

Yes, It's best to remove it, or lift one leg of diode to test. This will isolate it and eliminate parallel readings.
Best to use diode test function for testing. You should read a drop of about .3v forward biased, and infinite in the opposite direction.

 

[Alektron]

bushtech >>> " It's easier to test a schottky with an analogue MM. Have you got one? "

No I don't have an analog meter, I have a Klein 600 MM (multimeter), but I was thinking to by a cheap YX-360TRN Analog Multimeter off of ebay for only 12 bucks for this type of testings, that's gonna be my next purchase, along with a good brand of solder.

Tha flos agaibh >>> " Yes, It's best to remove it, or lift one leg of diode to test. This will isolate it and eliminate parallel readings. Best to use diode test function for testing. You should read a drop of about .3v forward biased, and infinite in the opposite direction.

I'm going to remove that Schottky diode. Let's see what it says outside the circuit. ( I'll get to it as soon as possible )

 

[Alektron]

Diode #23 will not move, nor would it lift up, no matter how much heat I ad, or additional solder to the tip of the iron. I'm not sure if it's the glue holding it in place (that black stuff underneath) or what else.

Any idea how can I remove this ? What I noticed is that, the L2 coil is in parallel with Diode 23.

 

[Alektron]

I cleaned out the three wholes at transistor Q8, using some extra solder and a copper wick. It was no easy task and it took me a while. The results might not be the best after all, but I'm not sure what else I could've done in order to achieve a better outcome.

 

[Tha fios agaibh]

Nice. Q8 will have a nice home to go to now.

Similarly for D23, you can use your solder sucker followed by your desoldering wick to remove most of the old solder. Then, you could use something like a toothpick to gently pry under one corner as you heat it. Adding a tiny dab of fresh solder to it will help with heat transfer. Once you feel it move up the tiniest amount, let it cool and then move the toothpick and soldering tip to the opposite side. Be patient and gentle. It will eventually come out. Pay close attention to its polarity so you remember its orientation.

 

[Alektron]

Tha flos agabh >>> Nice. Q8 will have a nice home to go to now.

Thank you, although it didn't turn out that great, at least for one side, but still better than I expected.

For D23, I'm thinking to get a de-soldering "Heat Gun", that would make life easier, what do you think?

 

[Tha fios agaibh]

I'm thinking to get a de-soldering "Heat Gun", that would make life easier, what do you think?

I think one can never have enough tools, but honestly it's not really necessary. I would much rather a good quality iron than a Chinese quality iron or heat gun. I believe the trick to have the right heat range. A heat gun is probably too hot.

You want an iron hot enough to bring the solder joint up to temperature in a few seconds, and not too hot where you bake the hell out of it. The tip or the solder joints should never be brown. Don't hold solder on the joint or iron for long because this with transfer heat away like a heat sink. Wait for it to come up to temp and then only briefly dab on solder when its needed. And the cardinal rule is to always keep the tip clean. I just use a damp cloth to wipe the tip. I alway wipe just before and after using it and probably every 30 seconds or so otherwise. when your not using an iron, unplug it.

There are pry tools that might be helpful in lifting components out but be careful not to use something that could cause damage.

If you have some patience and finesse that diode should pop up for you.

 

[73's de Edd]

Actually, at the D17 silkscreen marking, you have both the heavy wire gauge of the toroid AND a PCB copper square trying to steal your heat, while on the other diode lead, you have the whole ground plane pleading for and carrying off your heat.

ADD flux and fresh solder to both sides of the diode and built up 1/8----3/16 in balls
Grip diode center with tweezers rapidly move the immaculately tinned soldering iron tiplet back and forth between the balls, until you see a liquid / molten state onset . . .. rotate the tweezers about 15 degrees in either rotary direction to snap loose the adhesive bond while lifting upon the diode.
Test the diode in both low ohms mode and the diode test mode options of your meter.

 

[Alektron]

Tha fios agaibh >>> " If you have some patience and finesse that diode should pop up for you. "

Patience I have, but stable hands is what I would need, and some good eyes.

73's de Edd >>> "ADD flux and fresh solder to both sides of the diode and built up 1/8----3/16 in balls
Grip diode center with tweezers rapidly move the immaculately tinned soldering iron tiplet back and forth between the balls, until you see a liquid / molten state onset . . .. rotate the tweezers about 15 degrees in either rotary direction to snap loose the adhesive bond while lifting upon the diode. "

I'm going to do that.

" Test the diode in both low ohms mode and the diode test mode options of your meter. "

Ok, I will include some pictures, afterwards.

According to the spec sheet for this Schottky diode I should get a Forward Voltage around 550 mV
(at 2 Amps ), well we'll see.

For Spec sheet visit this link:
http://html.alldatasheet.com/html-pdf/101991/PANASONIC/MA738/484/1/MA738.html

 

[Alektron]

Diode #23 is out successfully. Please follow the pictures below.

I still get a 22 mV reading in Diode Test Mode with my DMM in Forward and Reversed biased scenarios.
Ohm test was reading 22 Ω, both ways (forward and reverse).


Conclusion: Are we having a shorted Schottky diode on our hand? I let you decide.

 

[Tha fios agaibh]

Good job. I would say its toast.
I love those ah ha moments.

 

[Alektron]

Tha fios agaibh >>> " Good job. I would say its toast. I love those ah ha moments. "

Thank you.

Going back to our schematic, is it possible that Diode #23 was our party pooper, and as an aftermath we are seeing a low voltage at pin #12 and #13 at the I-Flex Connector?

 

[Tha fios agaibh]

is it possible that Diode #23 was our party pooper
View attachment 39642

I would say highly possible. As to the reason for its demise, idk. Let's wait for 73's de Edds expert opinion on the matter.

In the meantime, check the surrounding components c44, c74, D24 as well (if you haven't already)

 

[Alektron]

Tha flos agaibh >>> "Let's wait for 73's de Edds expert opinion on the matter. "

Ok.

I was reading about this Schottky diode, and I like its description " A Silicon Epitaxial Planar type for high frequency rectification "

Next time I go to the local bar and a good looking chick is asking me what do I do for a living, I'll say:

" I'm a highly qualified technical expert in removing, testing and installing Silicon Epitaxial Planar type diodes for high frequency rectification on printed circuit boards"

I'm gonna sound so intelligent, she'll might think I'm a rocket scientist. ... Great Success !

 

[Tha fios agaibh]

Just don't tell her you were playing with your D23 yesterday but couldn't get it to move or lift up.

 

[Alektron]

I bought this analog multimeter for $12 today. It's gonna take me a while to get it, but that's OK, I'll have one of these in my arsenal for any occasion. It's a YX-360 TR N.

Still waiting on what brand solder I should get, any suggestions?

 

[Tha fios agaibh]

Good old-fashioned toxic lead solder.

https://www.amazon.com/gp/aw/d/B000...rosin+core&dpPl=1&dpID=51RayfITMPL&ref=plSrch

 

[Tha fios agaibh]

I bought this analog multimeter for $12 today. It's gonna take me a while to get it, but that's OK, I'll have one of these in my arsenal for any occasion. It's a YX-360 TR N.

Still waiting on what brand solder I should get, any suggestions?View attachment 39653

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.