R/E/P Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1]   Go Down

Author Topic: AKG C414 EB low output  (Read 546 times)

Kultivator

  • Newbie
  • *
  • Offline Offline
  • Posts: 3
  • Real Full Name: Jonas Olofsson
AKG C414 EB low output
« on: September 16, 2017, 10:46:58 am »

Hi, I´m having trouble with my C414 EB, it has very low output but passes sound. I´ve opened it up and checked the voltages on the DC converter card and I´m way off. Where it should be -60v , +60v , -20v I have -11v, +11v, -0,1v. I´ve got 9v at the zenerdiod like it is supposed to.
I´ve replaced the 10uf tantalum on the DC converter card with a 15uf I had lying around but no difference.

Does anyone know what voltage should be sent to the DC converter card, Voltage between the red and black wires? So I can try to locate where my problem is, if it´s the dc-converter card or something earlier in the circuit.

I read in some other thread that it could be the output transformer that´s broken, I´m told the phantom power  goes thru the transformer.
Please help!
Greetings from Stockholm.
/Jonas
Logged

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1423
Re: AKG C414 EB low output
« Reply #1 on: September 16, 2017, 05:21:49 pm »

You need to isolate the two sections of the mic amp- audio processor and DC converter section to determine where the short or voltage drain is located.

Disconnect the feed from the transformer to the mic amp (red and black wire), while keeping the DC converter connection intact.

If the polarization voltages still measure low, even when fed directly from B+ and bypassing any issues on the mic amp board, you know it is one of the components on the DC board.

If that is the case: I often find that tantalum capacitors deteriorate with time and short out. I would start with replacing them.
Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Kultivator

  • Newbie
  • *
  • Offline Offline
  • Posts: 3
  • Real Full Name: Jonas Olofsson
Re: AKG C414 EB low output
« Reply #2 on: September 17, 2017, 05:01:55 am »

Thanks Klaus.
Before I read your answer I disconnected the DC board, and then the voltages popped up to 29v(from 10) when I measure red-black, white-black over the transformer.

When you say "Disconnect the feed from the transformer to the mic amp (red and black wire)" is that the wires on top of the board? I´ve got 2 red wires and 2 black wires going to the pad and low-cut switches.
Logged

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1423
Re: AKG C414 EB low output
« Reply #3 on: September 17, 2017, 12:47:38 pm »

The fact that the voltage increased dramatically after disconnecting the DC board's electronics points to a component on the DC board, or, more likely, the 9.1V Zener on the DC board does its work, and that points even more to a shorting component on the DC board.

Methodically replace capacitors on the DC board with polarized electrolytics, particularly the 10nF and 22nF are suspect. If that does not bring up the voltage, which most likely it will, you need to check out the zeners, particularly the 9.1V.

P.S.: Leave the thin wires around the switches alone, They are not involved in this type of troubleshooting at the moment.
Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Kultivator

  • Newbie
  • *
  • Offline Offline
  • Posts: 3
  • Real Full Name: Jonas Olofsson
Re: AKG C414 EB low output
« Reply #4 on: September 18, 2017, 03:27:38 am »

Yes,I´ll try that. But first I would like to rule out the amp board, the amp board feeds the dc board with 8v when I measure black-red wire coming from the amp board to DC board and DC board disconnected. Isn´t that low?

One strange thing is when I engage the low-cut circuit voltage rises to 10v :-\



 
Logged

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1423
Re: AKG C414 EB low output
« Reply #5 on: September 18, 2017, 01:07:01 pm »

In your opening post you reported that you have 9 Volts at the DC board's Zener. That indicates that the  amp board is healthy, and the problem must be located on the DC board which is not pumping out the required high voltages for the capsule.

Hence my advice for troubleshooting the always suspect Tantalums on the DC board.
Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com
Pages: [1]   Go Up