Korg Vocal Sample

[Capacitorial]

Hello guys! I got a Korg Vocal Sampel here that doesn't get powered on.
I use it with six 1.5V Batteries (as stated on the back of the case).
Pressing the power button does absolutely nothing.

Visually I can not see anything wrong with the PCB.
The two soldering points where the PCB gets its power get 9.75V.
The power button seems to work, since on continuity mode it beeps when I press it.

I found out that the circled resistor (1M?) has 9V on the one side, and after the resistor there is no volage. No matter if I press the button or not.

Could this be the reason the thing is not powering up?

Picture here: https://imgur.com/a/FZTSx1i

EDIT: It seems to be a fuse and not a resistor. There is a writing beside it saying FU1. The SMD as a M on it

[stj]

Re: Korg Vocal Smample

good,
check the resistance between each end of the fuse and ground - lets see if there is a short-circuit responsible for blowing the fuse.

[Capacitorial]

Re: Korg Vocal Smample

Hi stj, thanks for your reply.
The upper pin where the 9.75 V are on, has no resistance to ground. After the fuse (lower pin on the picture) has 200 Ohms. (Settings on my DMM are Ohms 2k and display showing 0.222)

EDIT:

I searched for the datasheet of the voltage regulator on the picture. It is a TPS6211. Pinout of the chip: https://imgur.com/a/JiCuc1a

the pins 1 and 2 (VIN) are shorted to ground. Both pins go to a common smd capacitor. I guess the chip is dead?

[stj]

Re: Korg Vocal Smample

maybe, but smd ceramic caps are a common problem - i would remove the cap first and see if the short goes away.

[Capacitorial]

Re: Korg Vocal Smample

How can I find out the values of these caps? If they happen to be dead, I need to find a replacement.

[stj]

Re: Korg Vocal Smample

the chip datasheet often has example schematics

[Capacitorial]

Re: Korg Vocal Smample

You are right. Could you assist me on finding the right ones?

https://imgur.com/a/9CbLJ79

This is the example from the datasheet. I see three caps in proximity of the chip. On the datasheet example are not that many.

[budm]

Re: Korg Vocal Smample

According to the application circuit, the Vin (Pin 1, 2) filter cap are 10uF 25V and 1 uf in parallel, then also check to see if pin 8 (VNA) is also connected to pin 1 and 2.
You also need to check the resistance between SW pin and VIN pin, SW pin and PGND PIN.
BTW, what is the resistance reading between VIN pin and GND?
It is also best for us for you to use attachment function for the pictures instead of using off site for the pictures.

[Capacitorial]

Re: Korg Vocal Smample

Hello budm!
Pin 8 is connected to Pin 2, and Pin 1 (PGND).

VIN - SW : 3.3 Ohm
VIN-PGND : 3.3 Ohm

VIN - GND : 0.1 Ohm

[budm]

Re: Korg Vocal Smample

Hello budm!
Pin 8 is connected to Pin 2, and Pin 1 (PGND).

VIN - SW : 3.3 Ohm : This look bad, this measurement is to check the High side MOSFET of the SMPS IC

VIN-PGND : 3.3 Ohm: I expect this to be 0.1 Ohms also.

VIN - GND : 0.1 Ohm

How about SW - PGND, SW - GND? This is for testing the Low side MOSFET of the SMPS IC.
BTW, If you look at the internal diagram of the SMPS IC you will then understand why i ask you to check the internal MOSFET's of the IC.

[Capacitorial]

Re: Korg Vocal Smample

SW - PGND: 2.4 Ohm
SW - GND: 2.4 Ohm

Is it because if it is shorted than basically VIN is shorted to GND? I am a beginner with ICs

[Capacitorial]

Re: Korg Vocal Sample

So I found out that the parts and schematics are similar to the ones from another model of synthesizer.
Schematics: https://cdn.badcaps-static.com/pdfs/...ae6a5f9a79.pdf