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Where To Find The Power Blinking Fault In Yamaha PSR-3000 Keyboard?
The complaint of this Yamaha PSR-3000 Keyboard was power blink. It causes the LCD Display in the front panel to turn On and Off (the below photo showing when the display was On but after a second it will turn Of f again).
This kind of problem can be due to bad power adapter or the internal circuit board have bad component.
So where to find the power blink fault? The first thing I do was to isolate the problem by checking on the power adapter output. It showed 16 Vdc which means it was good. If you get improper dc output voltage then suspect the power adapter. In some cases, even when you got the good output voltage, this does not mean the power adapter is good. You have to test it with a load to see if the voltage can sustain or not. If can sustain the current draw this means the power adapter is good. If cannot this means the power supply regulation circuit or the secondary filter section have problem.
Since the power adapter was good so I had to open up the casing in order to look at the circuit board. Removing the cover was very easy.
The below photo is showing the low voltage and the main amplifier section. All the e-caps seems to be normal and no bulged e-caps found.
Next I powered On the keyboard and perform voltage testing on the 7812A voltage regulator IC. For a good IC, pin 1 must have 16 vdc (this supply is coming from the external adapter) and should produce 12 volt output at pin 3. Pin 2 is connected to cold ground-see the photo below:
But the defective IC have only 8 to 9 volt output and this is the reason why the LCD display blinks-see the photo below:
The original IC is an insulated type and did not connect to heatsink thus it can gets hot very fast. In my opinion, if I put back the same type it would not long also so I bought the replacement one where it can be attached to the heat sink. This way the IC will run cooler due to the heat can be dissipated fast-see the photo below how I have soldered the 7812 voltage regulator IC.
Once the powered was turned On look at the result below:
Conclusion- Voltage regulator IC (usually 1 ampere) play an important part in supplying the right voltage to the circuit. This means when the main board draws current the output voltage of the IC will maintain the same output voltage. The voltage can drop slightly but not too much otherwise it does not serve the purpose as a regulation device. You need to take note also that voltage regulator IC can breakdown when under full load. If you suspect the IC is bad just direct replace and retest. It is not expensive and you should keep some (variety output voltage such as 7805, 7812 etc) in your compartment. Ok that’s all for today and hope to see you again soon.
This article was prepared for you by Suranga Bandara who owns an Electronics shop in Anuradapura, Sri Lanka.
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