Help Troubleshooting Millenia Media HV-3B PLEASE

[moamps]

Sorry for the language barrier Moamps.
This is what I did:
-First I checked continuity between the pins indicated on the pic and it checked ok.

Then I checked that the female XLR connector on the chassis was properly connected to the 2 pins indicated on the pic and to ground.

Then I made a TRS-Male XLR cable to connect my soundcard, created a Logic session sending a 1khz sine to the cable.

Then I connected the scope probe on channel 1 and connected and and the probe end to U3-pin6 and after that to U4-pin6.

Perfect.
Connect the probe to XLR pins and find on scope your incoming 1kHz from the card. It can be around 100mV (adjust it in the software), and you shold see it on the scope. That's the start of tracing signal procedure. We can't evaluate some testing pins readings if we are not sure that signal is connected correctly into input or we are not sure how we shoud measuring it.

 

[sonolink]

Perfect.
Connect the probe to XLR pins and find on scope your incoming 1kHz from the card. It can be around 100mV (adjust it in the software), and you shold see it on the scope. That's the start of tracing signal procedure. We can't evaluate some testing pins readings if we are not sure that signal is connected correctly into input or we are not sure how we shoud measuring it.

Ok so I need to calibrate the oscillator to send a 100mV 1kHz sinewave into the preamp and after that I read U3 and U4 pin 6 with the scope, right?

 

[Ike Zimbel]

Ok so I need to calibrate the oscillator to send a 100mV 1kHz sinewave into the preamp and after that I read U3 and U4 pin 6 with the scope, right?

It's not clear to me if you have put the IC's back in or not (mostly because there's a pic just showing the sockets). If you haven't, start there.

 

[moamps]

Ok so I need to calibrate the oscillator to send a 100mV 1kHz sinewave into the preamp and after that I read U3 and U4 pin 6 with the scope, right?

First connect the oscilloscope probe directly between pins 2 and 1 and 3 and 1 on the input XLR and set your scope so you can see that signal nicely, for a few periods. Then connect the probe to the marked "XLR" points on the PCB
and let me know if you see that signal in those places either. Then we will continue.

 

[sonolink]

It's not clear to me if you have put the IC's back in or not (mostly because there's a pic just showing the sockets). If you haven't, start there.

The ICs are in because I'm reading the working channel

 

[sonolink]

First connect the oscilloscope probe directly between pins 2 and 1 and 3 and 1 on the input XLR and set your scope so you can see that signal nicely, for a few periods. Then connect the probe to the marked "XLR" points on the PCB
and let me know if you see that signal in those places either. Then we will continue.

Ok Moamps
I will tomorrow morning and report back
I'm in a gig right now.
Thanks for your help.
Cheers
Sono

 

[sonolink]

Hi again,

I can confirm that I see the signal in all those spots. The scope receives a 2mV 1kHz sine sent from Logic at -12dB.
Ready to continue

 

[moamps]

Something is wrong. -12dB (dBu, dBV nor dBfs) cannot give only 2mV. Picture of the scope display?

 

[sonolink]

I took a video

 

[moamps]

That's the noise from your laptop's power supply.
The picture should look like this:

 

[sonolink]

Sorry, I don't know why I was getting that. I routed the signal through Left Channel of Main Stereo Output and now I get this on all indicated spots.
Sine 1kHz 0dB

 

[moamps]

Reduce the input signal to about 100mV, about -20dB dBfs and send the scope picture.

 

[sonolink]

Like so?

 

[moamps]

Yes, now confirm you get this on two points on PCB named XLR, these are one legs of the input capacitors C7 and C9, measure the voltage on the other legs as well and send them.

 

[sonolink]

Confirmed

 

[moamps]

other legs of C7 and C9?

 

[sonolink]

Ooops sorry here you go

 

[moamps]

now post pictures of points A, B, C and D

 

[sonolink]

Here goes. Preamp is switched on btw

 

[moamps]

are U3 and 4 in the sockets?
post pictures of pins 6 of u3 and 4