Sound Skulptor forums

Build help and troubleshooting => MP566 Tube microphone preamplifier => Topic started by: Animorph on January 25, 2025, 11:56:58 AM

Title: MP566 not working.
Post by: Animorph on January 25, 2025, 11:56:58 AM

I just built the MP566, I am doing the tests without the output transformer but I can't get any voltage on TP2, I checked the usual suspects, everything seems fine.(https://i.imgur.com/nDbRnc8.jpeg)(https://i.imgur.com/AzpxHeu.jpeg)

Title: Re: MP566 not working.
Post by: JPK on January 27, 2025, 03:48:53 PM

Can you report the DC voltages on the 8 pins of U4, against 0V (beware of short-circuits with the probe tip!).

Title: Re: MP566 not working.
Post by: Animorph on January 27, 2025, 04:17:04 PM

1 -> -7.26V
2 -> -6.43V
3 -> -7.09V
4 -> -15.04V
5 -> -12.11V
6 -> -6.27V
7 -> -6.27V
8 -> -9.24V

Title: Re: MP566 not working.
Post by: JPK on January 27, 2025, 05:49:05 PM

The V+ voltage doesn't seem to get to U4 pin2.
Check the solder joints on the vertical to main PCB connections and on D14.
Remove U4 an measure again the DC voltage on pin2. It should be +15V.

Title: Re: MP566 not working.
Post by: Animorph on January 27, 2025, 06:10:19 PM

I did a continuity test on all the pcb connections, all were fine. The voltage on pin2 without U4 is -2.6V.(https://i.imgur.com/XcFogY7.jpeg)

Title: Re: MP566 not working.
Post by: JPK on January 28, 2025, 04:53:19 PM

Do you have +15V on the V+ test pin?
Check the diode D14. No need to didconnect it.
https://www.fluke.com/en/learn/blog/digital-multimeters/how-to-test-diodes

Title: Re: MP566 not working.
Post by: Animorph on January 28, 2025, 05:10:40 PM

The voltage on V+ is -3.9V. As for the diode test:(https://i.imgur.com/egqiNjr.jpeg)(https://i.imgur.com/ijUPk5I.jpeg)

Title: Re: MP566 not working.
Post by: JPK on January 29, 2025, 05:14:45 PM

Check the continuity between the V- test pin and the V- finger on the card connector pin 14 (second finger from the bottom).

Title: Re: MP566 not working.
Post by: Animorph on January 29, 2025, 05:21:42 PM

no continuity between them.

Title: Re: MP566 not working.
Post by: JPK on January 31, 2025, 12:11:07 PM

Check the solder joints on D13, L2, PTC2.
Check the resistance of L2 (less than 1ohm).
Check the resistance of PTC2 (around 1ohm).
Check (https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-test-diodes?srsltid=AfmBOooU02ihB6Vu0S-otiKYe4pfPZIiJSKX7IOLaU3aG-rsX36keCg-) D13.

Title: Re: MP566 not working.
Post by: Animorph on January 31, 2025, 02:51:14 PM

The solder joints are all fine. D13 is also ok. L2 is 0.2 ohm, PTC2 is 1.1-1.2 ohm.

Title: Re: MP566 not working.
Post by: JPK on February 01, 2025, 09:07:21 AM

no continuity between them.
This must be checked in the diode mode, red probe on the V- est pin.

Title: Re: MP566 not working.
Post by: Animorph on February 01, 2025, 09:13:11 AM

(https://i.imgur.com/2q3F8QY.jpeg)

Title: Re: MP566 not working.
Post by: JPK on February 01, 2025, 09:24:41 AM

Remove the tube, remove U1 and U4, place the phase switch in the center (mute) position and check again V-.
If you are still not at -15V, look for a component that is getting too hot.

Title: Re: MP566 not working.
Post by: Animorph on February 01, 2025, 09:31:18 AM

After removing the said components, I am getting -15.25V between V- and oV.

Title: Re: MP566 not working.
Post by: Animorph on February 01, 2025, 09:38:09 AM

But I was getting -15V on V- without having to remove the components, what I'm not getting is the +15V on the V+ test pin.

Title: Re: MP566 not working.
Post by: JPK on February 01, 2025, 09:54:26 AM

Sorry, my mistake.
Same questions as before but for +15V:
- Continuity between finger and V+pin
- Voltage on V+, after removing the components.

Title: Re: MP566 not working.
Post by: Animorph on February 01, 2025, 10:09:41 AM

The diode test between the V+ finger and test pin shows up at 0.6V, so I'm assuming it's fine. With all the components listed removed, V+ is at -1.18V, no component on the circuit board is getting too hot, all are cool to the touch, also there is no burning smell.

Title: Re: MP566 not working.
Post by: Animorph on February 01, 2025, 03:25:54 PM

I found out the problem, I had reversed the polarity of D12, everything works fine now! :)

Title: Re: MP566 not working.
Post by: JPK on February 01, 2025, 04:21:48 PM

(https://fonts.gstatic.com/s/e/notoemoji/16.0/1f44d/32.png)