SE Electronics Z3300a

[Khron]

And since the wires between the two boards were the way they were i would also check the wires within the transformer "case".

Ahem.....

 

[micolas]

R1 = 48,5Ω / R3 = 2,2KΩ
the 4 resistors are OK so are the 2 inductors...

unsolder R5 of 4.7k toward to C5 and measure
If it's good, leave it unsoldered,
stick R4. R2. R1. R3 in place and power the microphone
if it still manifests itself, you have a short circuit to which the transformer connections

 

[Emmathom]

Ahem.....

Yes, that's what is left now... the transformer area (as I said before)

 

[Emmathom]

unsolder R5 of 4.7k toward to C5 and measure
If it's good, leave it unsoldered,
stick R4. R2. R1. R3 in place and power the microphone

Ok. R5 desoldered (4,7KΩ indeed) and now give me some mn to resolder R1-2-3-4 and power on...

 

[Khron]

unsolder R5 of 4.7k toward to C5 and measure

Sure, worth a try, but resistors rarely (read: pretty much never) fail short-circuit...

R5 desoldered (4,7KΩ indeed)

Figured as much... Even if the capacitor was completely shorted, a 4k7 load would not have dragged down the power rail down to under 2v.

 

[micolas]

Sure, worth a try, but resistors rarely (read: pretty much never) fail short-circuit...



Figured as much... Even if the capacitor was completely shorted, a 4k7 load would not have dragged down the power rail down to under 2v.

let's also eliminate any defects from the audio circuit up to the transformer

 

[Emmathom]

2,5v at all the R and the 2 L (down the board) with 4,7KΩ unsoldered...
Are we gonna check now what's inside the "bell" of the transfo ???

 

[micolas]

2,5v at all the R and the 2 L (down the board) with 4,7KΩ unsoldered...
Are we gonna check now what's inside the "bell" of the transfo ???

the bell that shields the transformer must be opened and the situation of the wires must be seen

 

[micolas]

but first, disconnect the microphone and measure if there is a short circuit between gnd and the ends of resistors R4 R3

 

[Emmathom]

but first, disconnect the microphone and measure if there is a short circuit between gnd and the ends of resistors R4 R3

12,75MΩ (mega-ohms) between ground and R4 & ground and R3

 

[Khron]

let's also eliminate any defects from the audio circuit up to the transformer

How exactly would anything there, drag down the DC tapped off the transformer's secondary??? I would love a (rational) explanation.

The audio circuit's only connected to the secondary, and the power rail, through that 4k7 that was measured good.

As i said, even if that was between the power rail and ground, the voltage "before" that would end up around 22v (4k7 load, 1.1k+3.4k equivalent resistance in series with the phantom supply).

measure if there is a short circuit between gnd and the ends of resistors R4 R3

If there is one, it won't be a direct short circuit - 1-2v between that point and ground would mean about 200 ohms or so.

Are we gonna check now what's inside the "bell" of the transfo ???

I don't know, are we?????

And since the wires between the two boards were the way they were i would also check the wires within the transformer "case".

I "only" suggested this an hour and a half ago...

 

[micolas]

measures ohmic resistance between C4 and GND
is the primary of the transformer:
140.2 ohms

 

[Emmathom]

I "only" suggested this an hour and a half ago...

... and me from yesterday's night...

 

[Emmathom]

measures ohmic resistance between C4 and GND
is the primary of the transformer:
140.2 ohms

123,7Ω

 

[micolas]

I wanted to rule it out completely R5 4,7k
BJT 1015 and R6 1.5k burned out among OTHER faults

 

[Khron]

I wanted to rule it out completely
BJT 1015 and R6 1.5k burned out among OTHER faults

Silicon does indeed usually fail short; resistors don't. Even if the BJT was shorted, the resistor would've seen maybe ~300mW, if my math isn't too far off. Not exactly "burn" territory...

 

[micolas]

Silicon does indeed usually fail short; resistors don't. Even if the BJT was shorted, the resistor would've seen maybe ~300mW, if my math isn't too far off. Not exactly "burn" territory...

you can't know who 'worked' before in the microphone and how
I mean a defect caused by someone involuntarily

 

[Khron]

While that is of course true, all(?) of the soldering looks pretty "factory" to me. But what do i know?

 

[micolas]

While that is of course true, all(?) of the soldering looks pretty "factory" to me. But what do i know?

but you can accidentally touch something when measuring

 

[Emmathom]

XLR side : MΩ's between T1 & T2 - T3 / 152Ω between T2 & T3