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Need a solution for my 100v rated unit

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tronik101

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Hi Guys, I'm new here. Need help for my Clavinova which is Japan version rated 100v 55w. Our supply here is rated 220V. I don't want to use a step down transformer. Attached is the schematic of the power supply part. If i'm correct, I find 2 secondary windings with AC output of 12v and 5v. Now my question is, if i can't find a transformer with equivalent AC output, can i use 2? I'm thinking of using an ATX power supply bypassing the regulators but i have no idea what is the +B on the diagram. What transformer rating to look for, 12v 0v 12v, 0v 5v?

Note:
IC1 = +5v regulator
IC2 = +12v regulator
IC3 = -12v regulator
D1, D2 = 3A 200v diodes

View attachment 67327

Need any ideas, thanks
 
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you can replace your transformer with two others with equivalent outputs. you can also use PC power supply.
your image does not show entire circuit so my guess is that +B is trickle charge for battery (if one exists)
 
thank you, here's the the entire circuit, it's an old Yamaha Clavinova CLP-560 model. So the replacement would be rated 12v 0 12v and 0v 5v output? How about the current, 2A-5A? Btw, I'm just a hobbyist who loves DIY.

View attachment 67345
 
I just opened the unit and i found 3 input wires on the transformer, colored Brown, Yellow and Grey. Attached is the Circuit Board, it's the same as seen on my unit, on CN3 - Pin1 with the Yellow wire and Pin5 with the Grey wire, Pin 2-4 has no connections on the board, Brown wire is on Pin3.

Brown wire might be for 220v input of the transformer? Can't find any info about the transformer alone in the repair manual.

View attachment 67347 View attachment 67348 View attachment 67349

Ah, brown wire might be for 120v input.
 
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from what i can see brown wire does not connect to anything on the PCB, three middle pins of that connector are not used, only pins 1 and 5 (yellow and grey wire) are used. in Japanese model they are meant for 100VAC. if you can test it on 100VAC, you can measure voltage on brown wire (relative to gray). if you read some 200-230V, you are lucky. just carefully extract yellow and brown wire from the connector and swap them around.

transformers are easy to test with help of low voltage AC source (for example another transformer). one first identifies which wires belong to same winding, then connect low voltage source to any of the windings of unknown transformer and measure voltages on all of it's windings. rest is very simple math. if readings are low, connect source to some other winding and repeat test. be careful as small transformers usually have high ratio so powering secondary from low voltage source will produce high voltage on the primary.
 
A 12VAC transformer won't work. You need 24V center-tapped.

12VAC has a peak voltage of 17V which is reduced to 16.2V by the bridge rectifier at the input of the 12V regulators which is fine.

5VAC has a peak voltage of 7.07V which is reduced to 5.47V by the rectifiers at the input of the 5V regulator which is too low for an ordinary 5V regulator that needs at least 6.5V or more.
 
@panic mode i found the parts list, power transformer is rated 4A, built for Japan, US and Canada. The brown wire is unfortunately 120V meant for Canada i guess.

@audioguru Output reading of the transformer is 23VAC and 9VAC on a 110VAC source.

so i need 12V 0 12V, 0 9V?
 
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Canadian mains electricity is different in different parts of the country. 110V, 117V or 120V.
Mine is always 121V.

Why not calculate the DC voltage yourself?
9VAC x 1.414= 12.7 peak.
The rectifier bridge has two diodes in series conducting a short-duration high current so they reduce the voltage to 11.1V.
The ordinary 5V regulator needs an input of at least 6.5V so it works fine. But if the current is high then the regulator will get too hot unless a heatsink is designed to remove the heat.

Simply calculate the heat:
1) For example the current is 1A.
The voltage across the regulator is 11.1V - 5V= 6.1V.
The heat is volts x amps which is 6.1W.

Good electronic parts distributors (Like Digikey) allow you to search their website for a heatsink that can properly remove the heat.
Or you can bolt the regulator to a piece oif metal and burn out the regulator over and over until the heatsink is big enough so the regulator does not melt.
 
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Your transformer is probably the same as an export model, so the brown wire would be used for 220/240v systems and the yellow wire for 100/120v systems. They just use the yellow and leave the brown disconnected.

You could replace the mains fuse with say a 2A slow blow and try connecting the brown wire instead of the yellow one. If the brown wire is not a 220v tap then it will blow the fuse.

If you have test equipment you could measure the inductance of the brown-grey winding compared to the yellow-grey. Other safe tests would be to use a 100W lightbulb in series with the mains wire and then test the brown wire.
 
what would be the inductance difference if the brown-grey is for 220v? might be doubled of the yellow-grey value? i'll try with my WT3 woofer tester to check the inductance. i didn't do the test because of the part # is XE994A00 100v/120v

XE994A00 - Japan, US, Canada Models
XE996A00 - North European and British Models
 
i might be lucky :) i found 3 windings on the primary. can't use the WT3 tester might be because i didn't separate the wires.

result:
G & B: <.05mH - DC 12.46 Ohms
G & Y: >100mH - DC 9.785 Ohms

Have to separate it tomorrow and look for possible longest winding combination?

View attachment 67400
 
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Remove the xformer. Grab any low voltage transformer such as 6.3 V and fuse the secondary at a low value. Apply the 6.3VAC to the secondary of the instrument transformer.

Measure the voltages. Normalize the orange/orange to 8VAC and adjust the other readings accordingly by the same percentage. 5*1.414 = 7.07 and then there is 2 diode drops so it puts the voltage at 7.07*0.6*2 or about 8V

Now, you can figure out the primary taps.

Transformers will operate in reverse. They are just not as efficient.

You can do it to the other secondary as well. The idea is you need about 3 V more DC than the regulated voltage.

Since we don't know if the secondary is exactly 8 VAC, renormalize the adjusted primary voltages until they make sense.

For instance, if you measured 94.4 and 189 with a 6.3V input, the likely primary would be 120/240, but it won't be perfect.
120 94.5
240 189


Just get the raw data and we can make sense of it. From the schematic the primary voltages increase and those are the numbers you want. A single reference where the voltages increase.

Alternatively +-12, and +5 surplus or new power supplies should be common. Examples: **broken link removed**
 
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Hi Guys, can't find a single 220VAC/12V-0-12V, 0V-5V transformer, i decided to rewind the transformer. Unfortunately i have to rewind both primary and secondary windings, the primary can't be accessed unless i unwind the secondary.

Original primary winding was:

AWG #22
305 turns for 100VAC
305 + 61 turns for 120VAC

My conversion was:
AWG #25
376 turn for 220V

Secondary output: 17.3V-0-17.3, 0-7.5V

View attachment 68295 View attachment 68296 View attachment 68297 View attachment 68298

thanks for all your inputs guys :)
 
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You need to maintain the same turns-per-volt value as the original transformer.

If your primary had 305 turns for 100VAC, it will need 670 turns to run on 220VAC.
 
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