AKG 414B ULS Help

[hazmatstrat]

Hi,

I have been reading in this forum for years now and have learned a lot from many of the posts here.

I have a n AKG 414B ULS that has no output from the capsule. I have attached the schematic and would like some help in trouble shooting this mic.

I traced the voltages from the XLR connector and found the voltage drops very early in the schematic and does not supply the capsule with the required 62v.

The voltage out of the transformer is 39v, after r118 it is 38v. The voltage at the connection point of T105,T107, T108 and C106, should be 10.5v. at that point, the voltage is 0.42v.

What would be the best way to find the problem. I have thought about replacing T105, T107, T108. However I cannot find a good source for these trnsistors.




http://www.akg.com/mediendatenbank2/psfile/datei/51/c414B_ULS_412c87df992e6.pdf


Thanks in Advance,
Jim

 

[Gus]

First thing I would try is to check/replace C106

 

[hazmatstrat]

Hi Gus,

I replaced C106, C114, C05, C06, C08 and C11. I am waiting for an order of tants to replace the rest. When I tap each component I can hear sound through headphones. 0.04v voltage @ pin 5 & 6.

Thanks
Jim

 

[Rossi]

Check all caps for capacitance *and resistance*, C110 and also C113 and C114 would be likely candidates. Keep in mind that tants often fail dead short.

C414 are notoriously difficult to troubleshoot. I have a C414EB P48, and in the end it was the transformer that was faulty, not the tants as I had suspected initially. I did replace the cap in front of the transformer, though.

 

[hazmatstrat]

Thanks Rossi,

I have checked most of the caps and will be replacing most of them when I have a chance. On the 414EB that you have was the mic completely dead, or were you getting any sound from the mic? When I tap the components, I do get sound through the headphones. How did you test the transformer to determine it was dead?

Thanks again,
Jim

 

[Rossi]

It's been a while. I think there was no sound at all or maybe a very faint sound.

I measured the DC resistance of primary and secondary, and there was no continuity between one side of the primary and the center tap. Luckily, it was a broken wire just below the covering tape. So I was able to solder the wire together, carefully, and everything was fine again.

 

[vlh]

I borrow this thread as there is the link to ULS schematic in the first post.

I have quite old 414 ULS (possibly year -92 -model) which has a hiss -problem. The hiss used to go off by tapping the mic gently, but has now become constant. The capsule is quite dusty and dirty and I might consider to exchange it anyway, but my quess is that it´s not the capsule that is causing the hiss.

Can it be just a broken component or cold joint or what? Any ideas how to trace the problem?

Thanks in advance.