Roland RE-201 power supply board repair problem

[shady313yo]

Hi everyone, I'm having some difficulties repairing my Roland RE-201 and would like your help.
Problem description: The output voltage of pin 40 of my Roland RE-201 power board is about 12V, but according to the specification, it should be between 16-17V.
In addition, the device also has the following problems: the VU pointer keeps jumping, and crackling noise can be heard if the power amplifier is connected. I suspect that these problems are caused by insufficient output voltage.
Inspections and repairs carried out:
Preliminary check: I checked the red area on the power board, specifically the resistance of R109, and found that the resistance of R109 was 192 ohms, I have replaced this resistor. Situation after replacement: After replacing R109, the output voltage is still 12V, and there is no improvement. The VU pointer is still beating, and the crackling noise still exists. I also checked all the parts in the blue area and found no faulty components.
Can anyone give me some advice?
（Should I consider disconnecting the two leads of the pin 40 output to make sure the low output is not caused by the load?）

 

[Khron]

How about following the schematic and veryfying that you ARE indeed getting 21V or so before the regulator for that supply rail? That's kinda-sorta what that "21V" is there for...

 

[shady313yo]

How about following the schematic and veryfying that you ARE indeed getting 21V or so before the regulator for that supply rail? That's kinda-sorta what that "21V" is there for...

Thank you for your answer. I tried to use the black test lead of the multimeter to connect to ground. The red test lead was connected to C or E of Tr21. The value I got was 25V or 24V. In addition, it seems that it was because I made a mistake in measuring D11 and D14 with the black and red test leads, which caused the fuse. It burned out, but I replaced it with a new fuse. I'm not sure if it's the fault of D11 or D14. I don't know how to judge whether they are good or bad. What should I do next?（I also have a portable oscilloscope and if I need to use it to check a circuit, I follow the instructions.）

 

[shady313yo]

The latest update is that after I replaced C71 on the reverb echo board, I no longer hear the crackling noise. but The pin 40 still output 12.56V ，Soon after, the crackling sound came back again (I lost the echo delay)

 

[shady313yo]

Hello, everyone. I will announce the results of my measurement. I hope to know what should be done next.
C110 is measured with a multimeter to get 20.9V, and C108 is measured to get 14.9V.

 

[shady313yo]

Hope to get some help, will D10 on pin 44 and 46 affect the output voltage of pin 40? I found that the value of D10 is not normal. I am not sure if it is because pin 40 affects D10 or if D10 affects pin 40.

 

[Khron]

Hope to get some help, will D10 on pin 44 and 46 affect the output voltage of pin 40? I found that the value of D10 is not normal. I am not sure if it is because pin 40 affects D10 or if D10 affects pin 40.

You're telling us that as if we magically know where D10 is, what it's connected to, or what it does.

What does that 16-17V (that's supposed to be at pin 40) feed?

 

[shady313yo]

D10 is connected to pins 44, 45, and 46. 44 and 46 are the bulbs responsible for the VU meter. It did not work, and the measured voltage was too high. I am not a professional maintenance person, so I may not be able to convey it to you accurately. The 16-17V on pin 40 should be responsible for powering the jack board and echo board.

 

[Khron]

Oh, noticed D10 in the first snippet of schematic after all.

https://resources.altium.com/p/using-flyback-diodes-relays-prevents-electrical-noise-your-circuits

No idea how you measured it, but that's in parallel with the coil of relay SW2 (reed relay?).

If those VU meter bulbs are burnt, "of course" the voltage will be too high there, since there's nothing left to load down that voltage rail. Pretty sure that has nothing to do with the other / initial problem you described, though...