D47 Rookie mistake

[geekmacdaddy]

I brought some mic's to a friend's studio so his wife (Bulgarian Opera singer) could try them out. We did the 251 and C12, then he plugged in the D47. No signal. As it turns out he had left phantom power on. Rookie mistake from a very experienced engineer. B+ is sending signal, 408a's are not lighting up. Can someone give me a starting point? Did he blow up Moby's beautiful tx, or do I get off easy with a blown up cap?
Thank you
Oh, here's the links to the D251, and D12;
https://www.dropbox.com/s/dqj52suw7xlhqoy/ANNA 251 Sample 2.wav?dl=0
https://www.dropbox.com/scl/fi/c73w...le-2.wav?rlkey=xnor0aqhwz4y9s82upybe4fbv&dl=0

 

[Khron]

How about whipping out a multimeter and measuring the transformer's secondary, thereby rendering moot the need for any speculation?

Although if the heaters(?) aren't lighting up... Where did you measure that B+?

 

[thomasdf]

Unless wired wrong the phantom power should not damage a transformer, right ? No current ?

 

[geekmacdaddy]

How about whipping out a multimeter and measuring the transformer's secondary, thereby rendering moot the need for any speculation?

Although if the heaters(?) aren't lighting up... Where did you measure that B+?

First I checked the power supply (obviously, I'm not experienced w/troubleshooting mics) and made sure B+ was coming from there. Then I tried to measure both primary and secondary's but got nothing. What is the correct place to take ground?

 

[Khron]

Then I tried to measure both primary and secondary's but got nothing. What is the correct place to take ground?

"Tried to measure"... voltage or resistance?

The entire microphone body should be connected to ground (even mains earth, when connected to the power supply).

 

[geekmacdaddy]

How about whipping out a multimeter and measuring the transformer's secondary, thereby rendering moot the need for any speculation?

Although if the heaters(?) aren't lighting up... Where did you measure that B+?

First I checked the power supply (obviously, I'm not experienced w/troubleshooting mics) and made sure B+ was coming from there. Then I tried to measure both primary and secondary's but got nothing. What is the correct place to take ground?

"Tried to measure"... voltage or resistance?

The entire microphone body should be connected to ground (even mains earth, when connected to the power supply).

voltage

 

[Khron]

voltage

Well, not getting any (DC) voltage reading there is a good thing. I was actually hinting at measuring resistance (with the power OFF) of the mic transformer windings.

After that, you can turn the power back on. Is the B+ reaching the microphone?

Just because the PSU seems to work, doesn't mean the cable or some other connection, between the PSU board and the mic board, can't be faulty.

PS: If this is your build, how much do you really trust that ancient PIO cap?

 

[geekmacdaddy]

If I have measured resistance properly, 17Ω on primary's, 640Ω on secondary's (no power). I unplugged the the output jack of the PS that goes to preamp (power on), got no continuity between pins 2 and 3 which read 640Ω. Are my secondary's blown?

 

[Khron]

If I have measured resistance properly

I could be wrong, but sounds like you didn't. That, and/or there's a language barrier (regarding terminology) somewhere...

The microphone transformer's primary winding is between one end of that "West-Cap" capacitor, and ground. That same transformer's secondary winding is between pins 2 and 3 of the 3-pin XLR output connector, on the power supply.

After that, you can turn the power back on. Is the B+ reaching the microphone?

Just because the PSU seems to work, doesn't mean the cable or some other connection, between the PSU board and the mic board, can't be faulty.

Ahem........

 

[geekmacdaddy]

That same transformer's secondary winding is between pins 2 and 3 of the 3-pin XLR output connector, on the power supply.

That is what I measured. Yes B+ reaching the microphone.

 

[Khron]

That is what I measured.

17Ω on primary's, 640Ω on secondary's

Did you manage to connect the transformer back-to-front? Or, as i suspected above, there's (also) a terminology-barrier somewhere in the way...

 

[rock soderstrom]

If I have measured resistance properly, 17Ω on primary's, 640Ω on secondary's

Khron could be right, it seems your OPT is wired backwards. Can you show some good photos of the OPT and its wireing?

 

[rock soderstrom]

check this - "Wicklungswiderstand" means DC resistance of the coils:

 

[Khron]

Yes B+ reaching the microphone.

Still a bit on the vague side.



Pardon my "stunning" annotation skills, but i wanted to make it nice and visible.

"P" and "S" should be the Primary and Secondary windings. With the power off, primary should have (waaaay) higher resistance than the secondary.

With the power on, what are you measuring between ground and the indicated "B+", and between ground and "B+2", respectively?

PS: Triple- or quadruple-check the PCB-to-connector wirings (both inside the PSU and the mic), as well as the cable itself. "There's no easier person to fool than yourself" - AvE

 

[geekmacdaddy]

Did you manage to connect the transformer back-to-front? Or, as i suspected above, there's (also) a terminology-barrier somewhere in the way...

First, thank you for bearing with me Khron. I hope this isn't disrespectful. I don't know the terminology "front to back". l didn't see your photo. When I get back from shipping I'll give it the proper look and testing. Thank you

 

[Khron]

I don't know the terminology "front to back".

The primary wires soldered to where the secondary should go, and vice-versa.

 

[geekmacdaddy]

Khron could be right, it seems your OPT is wired backwards. Can you show some good photos of the OPT and its wireing?

I recorded with it the day before, it always worked well... photo done in haste, have to ship something but will return for more info in an hour.

 

[Khron]

I recorded with it the day before, it always worked well... photo done in haste, have to ship something but will return for more info in an hour.

Pretty sure that's back to front.



See those S-, S+, P-, P+ designators there, at the bottom of the board? Did you think they were put there randomly, and/or for no reason?

Isn't the primary supposed to be red/black, and the secondary blue/white?

 

[geekmacdaddy]

See those S-, S+, P-, P+ designators there, at the bottom of the board? Did you think they were put there randomly, and/or for no reason?

Between dyslexia and the German language, there's enough to here to confuse an American amp/pedal builder. No, I didn't think they were random, and I understand the difference between Primary and Secondary windings.
I switched primary and secondary connections to the board. HR1 no voltage. B+ and HR2 getting 78v (on the board). P2 and P3 on output of the P/S, no continuity, meter reads offline. Primary's getting 670Ωish (measured on the board). Secondary's 17Ω.

 

[Khron]

HR1 no voltage

What's HR1 connected to/ supposed to be? Ground, or...?

B+ and HR2 getting 78v (on the board

Well that's no good...

P2 and P3 on output of the P/S, no continuity, meter reads offline.

What's P2/P3?