QRV08 Setup Instructions

[peranders]

The goal is to get 0 mV on the output, do you get that? You should also have a voltage on pin 6 of the DC servo opamp which is somewhere within ±11 V. The opamp must not be saturated.

[BMF]

The power supplies and regulators function perfectly. No issues. I cannot find any component errors at the amp sections and no cold joints or resistance issues. As you've said before, when the same problematic measurements are found on both sides, there's probably incorrect component values somewhere.

I get 12 vdc on both sides of R3/E3.

R1/E1 measure 0.5 to 0.8 vdc.

IC 1 and IC 3 are saturated at Pin 6=-13.6 vdc and Pins 2 and 3 are not equal and range between 200 to 300 mV.

With no jumpers, P1 and P2 have little to no effect on offsets, CW as well as CCW; same for R1/E1. And, shorting the inputs makes no difference.

Jumpering or no jumpering does not change -13.6 vdc at Pin 6 of IC1 or IC3.

Since the sound quality remains good (I'm using AKG 7 XX and Sennheiser 650) and my measurements are unreliable from one "testing session" to the next, I wonder if I'm going about measurements all wrong?

As always, thank you for your help.

[peranders]

I think you don't understand what I want to know.

Adjust the input bias and observe the voltage on pin 6 of the DC servo opamp and the amplifier output. Notice the pin 6 voltage when you still have 0 mV at the amplifier output. What I want to know is if the DC servo is in its linear range.

[BMF]

The positive rail on the Right Channel of my second build suddenly failed after several hours of normal functioning.

I discovered that G49 on the positive side is shorted to ground at all grounding "holes" across the Right and Left channels of the regulators, and at the negative sides of regulator caps and resistors.

E55 to E53 are shorted on the sides closest to the negative side of G49/G39. I have not been able to determine the cause or specific component responsible for the short.

I changed out the following components on the failed rail with no benefit:

Regulator chip
Red LED
G49, G39
G37
E45, E55, E53, E57

The board is clean. I found no solder bridges or cold joints; no solder balls or other conductive debris.

[peranders]

The board is working now?

[BMF]

Sorry, no. I meant the board is clean of flux, etc. The positive rail on the Right is faulty.

I'll keep searching but I can't imagine why it worked for several hours and then simply stopped working; I had done nothing to it so the positive short to ground is puzzling.

[peranders]

Have you found where the short circuit is?

[BMF]

No luck, yet. I'll keep searching.