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Help Korg not turning on.
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Help Korg not turning on.
I unplugged my korg recently and plugged it in at a different socket and now the lcd displays nothing at all when I turn it on. I will attach a link to a video demonstrating what I'm talking about. Has anyone experienced this problem if so how was it resolved or does it mean my synth is now nothing more than i paperweight
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alfredokiwi
- Senior Member
- Posts: 268
- Joined: Wed Sep 07, 2011 9:23 am
Check step down converter 3,3 volts internal regulation, the R3 use a miniature MOSFET Si4431ADY and switching controller device to supply the main processor, memories, digital logic and DSP.
On the displays if the whole dots matrix is black showing ***** is an indication that they don´t receive initialization data from main processor. In other words the main processor is not running meaning that something wrong happened on the IC chips. The LCD units are powered up with a separated fixed linear regulator on 5 volts rails (BA05FP on the schematics) the reason why on power up LCD shows black dots **** and backlight is on.
After reading post about power failures on Korg R3 I decided to check on my R3 if P-channel MOSFET overheats to much. In such case the replacement with a bigger one is the solution for a safe operation on MOSFET current and power dissipation but the are other issues. Researching datasheets the PWM controller LTC1771 use an external feedback divider to set Vout regulation because is a resistors variable not fixed PWM controller and here a lot of problems begins due calibration issues..., explanation below for the experts.
A variable voltage PWM controller is very unstable due noises or calibration issues on the Vout (VFB on circuit) feedback resistors. At the same time "cold solder joints issues" can lead to sudden Vout fluctuations or "out of regulation PWM behavior". An internal fixed 3,3V PWM controller is the ideal choice on a design for a safety Vout sensing and components simplicity. Another issue what I see on the design is the use of SMD resistors in the million of ohms (Mohm) range for the VFB feedback network (R119, R120, R123 on circuit diagram). Reading the datasheet the use of megohm values for Vout sensing is to guarantee stable regulation without load or at very low quiescent currents, but "The problem on tiny Megohm SMD resistors is the drift of its resistance due ambient temperature or aging because are very sensible and difficult to calibrate in tolerance". Also external factors for example PCB insulation/conduction or corrosion issues can drift the resistance value in Mohm ranges. "Because on Korg R3 the circuit is always under load the best here is to set the VFB feedback values in the Kohms range avoiding in this way further issues related to resistance drifts. At the same time the feedback impedance reflected on the comparator input VFB on LTC1771 controller is much lower improving the Vout stabilization."
"Low resistance values on a feedback network in the Ohm-Kohm range are better as Megohm values because are more stable on its calibration and reliable on operation without drift issues due aging."
For example lowering the feedback values by 10 will give R119=100K, R120=68K and R123=100K. The formula to calculate Vout is: 1.23 x ( 1 + (R119+R120)/R123).
1.23 is the internal fixed reference on VFB comparator.
Replacing with new values 1.23 x( 1 + (( 100+68 ) / 100 )) => 1.23 x ( 1+1.68 ) => 1.23 x 2.68 = 3.2964 volts. I will do that to lower feedback impedance by 10 for a better Vout stabilization increasing C87 by 10 => 50pf to compensate the lower impedance.
"It can be also lowered by a factor of 1000 improving more the voltage stabilization due the very low feedback impedance :
1.23 x ( 1 + (( 1+0.68 ) / 1 )) = 3.2964
Here the Vout feedback load is approximately 2,7 Kohm which represent a power consumption of only (3,3v / 2700 ohm)=>0.0012 A x 3,3 V = 0.004 W nothing comparing the operational consumption on Korg R3 in the range of watts"
Post below explains a similar failure on Korg TR but the good news is that the PWM controller is fixed at 5V, avoiding all the issues of an external feedback network for Vout set and sense.
http://www.korgforums.com/forum/phpBB2/ ... hp?t=89424
On the displays if the whole dots matrix is black showing ***** is an indication that they don´t receive initialization data from main processor. In other words the main processor is not running meaning that something wrong happened on the IC chips. The LCD units are powered up with a separated fixed linear regulator on 5 volts rails (BA05FP on the schematics) the reason why on power up LCD shows black dots **** and backlight is on.
After reading post about power failures on Korg R3 I decided to check on my R3 if P-channel MOSFET overheats to much. In such case the replacement with a bigger one is the solution for a safe operation on MOSFET current and power dissipation but the are other issues. Researching datasheets the PWM controller LTC1771 use an external feedback divider to set Vout regulation because is a resistors variable not fixed PWM controller and here a lot of problems begins due calibration issues..., explanation below for the experts.
A variable voltage PWM controller is very unstable due noises or calibration issues on the Vout (VFB on circuit) feedback resistors. At the same time "cold solder joints issues" can lead to sudden Vout fluctuations or "out of regulation PWM behavior". An internal fixed 3,3V PWM controller is the ideal choice on a design for a safety Vout sensing and components simplicity. Another issue what I see on the design is the use of SMD resistors in the million of ohms (Mohm) range for the VFB feedback network (R119, R120, R123 on circuit diagram). Reading the datasheet the use of megohm values for Vout sensing is to guarantee stable regulation without load or at very low quiescent currents, but "The problem on tiny Megohm SMD resistors is the drift of its resistance due ambient temperature or aging because are very sensible and difficult to calibrate in tolerance". Also external factors for example PCB insulation/conduction or corrosion issues can drift the resistance value in Mohm ranges. "Because on Korg R3 the circuit is always under load the best here is to set the VFB feedback values in the Kohms range avoiding in this way further issues related to resistance drifts. At the same time the feedback impedance reflected on the comparator input VFB on LTC1771 controller is much lower improving the Vout stabilization."
"Low resistance values on a feedback network in the Ohm-Kohm range are better as Megohm values because are more stable on its calibration and reliable on operation without drift issues due aging."
For example lowering the feedback values by 10 will give R119=100K, R120=68K and R123=100K. The formula to calculate Vout is: 1.23 x ( 1 + (R119+R120)/R123).
1.23 is the internal fixed reference on VFB comparator.
Replacing with new values 1.23 x( 1 + (( 100+68 ) / 100 )) => 1.23 x ( 1+1.68 ) => 1.23 x 2.68 = 3.2964 volts. I will do that to lower feedback impedance by 10 for a better Vout stabilization increasing C87 by 10 => 50pf to compensate the lower impedance.
"It can be also lowered by a factor of 1000 improving more the voltage stabilization due the very low feedback impedance :
1.23 x ( 1 + (( 1+0.68 ) / 1 )) = 3.2964
Here the Vout feedback load is approximately 2,7 Kohm which represent a power consumption of only (3,3v / 2700 ohm)=>0.0012 A x 3,3 V = 0.004 W nothing comparing the operational consumption on Korg R3 in the range of watts"
Post below explains a similar failure on Korg TR but the good news is that the PWM controller is fixed at 5V, avoiding all the issues of an external feedback network for Vout set and sense.
http://www.korgforums.com/forum/phpBB2/ ... hp?t=89424
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