Author Topic: No Mic Input And Saturation on DI

February 25, 2021, 08:30:23 AM
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Kev4272

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Hi! I just finished a MP566, but I don't have any Mic Input. The signal on the DI seems to work but there's a lot of saturation on it, its almost distortion. I checked the click on the gain switch and I have a click between the Low and the Mid but nothing for the High. I also have no click when I insert a jack in the DI. 

Thanks!

February 25, 2021, 06:31:09 PM
Reply #1

JPK

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The No Mic issue may come from a damaged 2N7000 (Q1). This component is sensitive to static electricity and is better handled without your shoes on (body grounded).
You can check this by creating a short between the 2 extreme pins of this component. It should activate the mic relay.


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I have a click between the Low and the Mid but nothing for the High
This is normal, the high gain is directly controlled by the switch, without a relay.

Do you have a gain variation between the mid and high gain?
Check the DC voltage on TP4. it should be close to 0.
JPK

February 28, 2021, 04:37:18 AM
Reply #2

Kev4272

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You can check this by creating a short between the 2 extreme pins of this component.
By the two extreme pins of the component, do you mean the 0V and the V+ ?

Do you have a gain variation between the mid and high gain?
Check the DC voltage on TP4. it should be close to 0.
I have a big difference of dB between the three of them. The Low gain is the loudest and the Hi Gain the least loud. But I don't really hear a lot of difference in terms of saturation between the three of them.

Do I have to put the black probe on the 0V and the red probe on the TP4? If yes, I am getting 0V

March 01, 2021, 05:08:59 PM
Reply #3

JPK

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Quote
By the two extreme pins of the component, do you mean the 0V and the V+ ?
NOOOO!

Q1 is a component with 3 pins in a row. I mean between the 2 pins which are not the center pin.


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Do I have to put the black probe on the 0V and the red probe on the TP4? If yes, I am getting 0V
Correct. This is OK.

JPK

March 03, 2021, 07:30:13 AM
Reply #4

Kev4272

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Q1 is a component with 3 pins in a row. I mean between the 2 pins which are not the center pin.
Alright! So I did it, but I don't hear the mic relay clicking. Does that mean that the Q1 is damaged?

March 03, 2021, 11:11:24 AM
Reply #5

JPK

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No, it means the issue is in the relay or R26 or D2.
If R26 and D2 are OK, try replacing the relay. Send me an email here for a replacement part.
JPK