n72 build troubleshooting

[svenc24]

Hi,

I have been trying to assemble 2 n72 v3.3 preamps and so far, they are winning.

This thread is for the first module.

I have gone through the BOM line by line to verify each component, its placement on the board, and its orientation. Checked the input and
output transformer wiring. Checked for solder bridges, bad solder joints, and checked the traces for problems / bits of solder/wire etc as best as I can.

When I check the power connector J1, Pins - 1 and 2 / 2 and 3 - I get high ohm readings.

I've Turned R39 counter clockwise until it clicks before applying power and when applying power I get the below Voltages:

Q1 - 3.7 | 2.2 | 1.7
Q2 - 12.8 | 3.7 | 3.1
Q3 - 21.4 | 12.8 | 12.2
Q4 - 0.9 | 0.7 | 0
Q5 - 0.2 | 0.7 | 0.2
Q6 - 0.2 | 0.2 | 0.2

Q6 did not change if I turned R39.
The input transformer wiring was 46.6v for 2,3,4, and 5. 0v for 7 and 10
The output transformer wiring reads Brown:23.2, Violet:0, Red: .02, Green:0, Blue:0, Orange:.02, Black:0, yellow:0

I've re-flowed all solder joints, rechecked everything mentioned above, made sure the screws for Q6 and the output transformer weren't too
loose or tight, and got the same results. Changed the battery in my DMM. Broke that DMM (it was cheap), bought a new DMM and outfitted it
with a new battery. Checked over everything again, same results.

I then re-flowed all the solder joints around Q4, Q5, and Q6 and got the below:

This time I could dial in Q6 with R39, great!
Although I didn't write them down, the output transformer readings looked much better to me.
And Q1-6 looked close to the assembly instructions.

Q1 - 3.7 | 2.2 | 1.7
Q2 - 12.8 | 3.7 | 3.1
Q3 - 21.4 | 12.8 | 12.2
Q4 - 4.0 | 0.7 | 0.1
Q5 - 22.2 | 4.0 | 3.4
Q6 - 22.2 | 3.4 | 2.9

I then got excited and turned the power off, didn't move the module, grabbed two xlr cables and plugged them in about 5 minutes later. Turned

the power on, and there was no signal. So I check the voltages again, and I was back at the first voltage readings.

I checked over everything again, input/output wiring, solder joints, top and bottom of the board, rechecked the transistors/cap/resistors
placement/orientation, and re-flowed the joints around Q4, Q5, Q6 again. And I am still at the first set of readings.

One thing that is a little different with the n72 v3.3 from the steps/pictures in the instructions we're the number of jumpers and the added

filters L 1-4. I see the filters in the schematic so I put them in. Are those suppose to be in the circuit or are they optional? It looks like conn 3 and conn5 are optional.

Any Ideas of something else I can check or try? Thanks.

Here are some pictures of where I am, ..the first set of voltages.

https://imageshack.com/i/id2IEo1vp
https://imageshack.com/i/idKG5ocgp
https://imageshack.com/i/ewUonDnlp

[svenc24]

Followed the following steps for testing transistors (http://electronicsclub.info/multimeters.htm / http://electronicsclub.info/transistors.htm)

Results:
(.0l = reverse biased)

Q1
BE: .68 / .0l
BC: .68 / .0l
CE: .0l / .0l

Q2
BE: .67 / .0l
BC: .68 / .0l
CE: .0l / .0l

Q3
BE: .66 / .0l
BC: .66 / .0l
CE: .0l / .0l

Q4
BE: .67 / .0l
BC: .67 / .0l
CE: .0l / .0l

Q5
BE: .67 / .0l
BC: .67 / .0l
CE: .0l / .0l

Q6
BE: .51 / .0l
BC: .51 / .0l
CE: .0l / .0l

Q7
BE: .59 / .0l
BC: .67 / .0l
CE: .0l / .0l

Q8
BE: .61 / .62
BC: .62 / .0l
CE: .7 / .0l

Diodes: (tested while still on the board..)
D1: .53 /.0l
D2: .7 / .48
D3: .082 / .082
D4: .53 / .0l

[svenc24]

This module is now working and sounds fantastic

[Doppleganger]

How did you get it working? I'm having the same problem. Can't adjust voltage. I re-flowed ever solder joint on the board and nothing changed.