Author Topic: MP566-II Phantom Power problem - signal fades to zero

July 29, 2026, 03:18:34 PM
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guenter1910

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Hi all, following my previous post about LD2 there is another problem that came up. When using Phantom Power, Everything works fine for a short while and than the signal fades away quite rapidly. The Voltage on IN+ and - is down to 28V when the 48V switch is engaged. What confuses me a bit is that on the kit C1 (100u, 63V) is packed but the partslist with C1 on is crossed out and on the new one C1 is no longer there. I have put C1 in initially and thought that this might cause the problem and so I desoldered it, but the behaviour is the same.
Any help highly appreciated!
Best regards,
Guenter

Today at 08:44:57 AM
Reply #1

JPK

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but the partslist with C1 on is crossed out
Make sure you are using the latest parts list. C1 must be populated.
Does the 48 V rail (on the finger connector, pin 15) remain stable when the voltage on the XLR drops?
What is the phantom voltage level on each side of R3?
JPK

Today at 01:54:25 PM
Reply #2

guenter1910

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Phantom Power on Pin 15 is stable (49,45 V), Voltage on R3 is 49,45V on one and 47,90 V on the other side, C1 populated again.

Today at 06:51:56 PM
Reply #3

JPK

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Check the resistance value between:
- XLR pin2 and pin3, 
- XLR pin2 and 0V,
- XLR pin3 and 0V.
Also check your mic cable.
JPK

Today at 07:37:30 PM
Reply #4

guenter1910

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XLR Pin 2 and 3 on the cable 29,4 Ohm, on the 500 Rack Slot 28,94 Ohm
Pin 2 on the cable to 0V on the board 22 MOhm
Pin 3 on the cable to 0V on the board 22 MOhm
both slowly increasing

Mic Cable is ok. I checked with a different cable - same behaviour 

 

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