Hey guys, I have this guy on my bench. No sound at all. Looks like missing capsule polarisation voltage, but I'm not sure because I have no schematics. I wonder does aomeone has schemo or experience with this little bastard?
![P_20170702_174244-648x1152.jpg](https://proxy.imagearchive.com/d73/d733947556989b2319ea885d65178e9f.jpg)
Most likely you have problem with DC-DC converter. Try to measure output voltage at the converter's output directly, you can't measure polarization voltages at capsule because this voltage bias is set via very high-ohmic resistors.Moby said:....but I dont measure any polarization voltage....
Thx. I think that I checked already but hey, double check cant do harm. Btw, I still dont understand (from the circuit) how they connected -50v to the backplateGus said:I would look for -50VDC on pin 6 and 7 of IC1
I would guess one of the backplates is at -50VDC and the other backplate is grounded with 1gig it is a multpattern capsule used as a cardiod
The outside is grounded
check for the -50VDC and +10VDC at IC2
Imagine a resistor inside hybrid IC1 MH101 connected from pin 6 to pin 7. There are now two possibilities: Capsule is shorted or MH101 is dead. You can check MH101 by injecting a signal via 50pF capacitor to pin 7 and observing the output (when capsule is disconnected).Moby said:...., I still dont understand (from the circuit) how they connected -50v to the backplate ....
Aha, u want to say that polarisation is achieved form the membrane side, right?moamps said:Imagine a resistor inside hybrid IC1 MH101 connected from pin 6 to pin 7. There are now two possibilities: Capsule is shorted or MH101 is dead. You can check MH101 by injecting a signal via 50pF capacitor to pin 7 and observing the output (when capsule is disconnected).
Actually, I tried this one on other impedance converter and it worksGus said:Have you tried another capsule?
yep, thx. Same approach recomended me my local colleague. Right now I'm on vacation and surgery will start at the end of this monthgyraf said:Epoxy is removed with a heat gun and a sharp knife....
Jakob E.
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