I am building an electronic "dice" that uses an ATTiny84 to sample avalanche noise from a 2N2222 in reverse-bias and generate random numbers, which are then displayed on 2 7-segment displays. 
When I prototyped this on a breadboard, it worked just fine, so I decided to move to "production" and put it on a PCB.
Unfortunately, the noise generator on the PCB is running into some issues: It does not seem to be outputting (the "output" is the collector of the 2N3904) a noisy signal.
Now, as I am a student with limited means, I would usually go into the university lab and use one of their marvelous oscilloscopes to troubleshoot the signals themselves; however, they have locked all the labs for renovation or something and I can't use their equipment.
Therefore, I am asking for some suggestions as to how to troubleshoot with the tools I do have: soldering/desoldering equipment and a basic digital multimeter. I have already confirmed that all of my traces are intact and going where they should, and that steady voltages are what they should be. Every other component of the circuit works like a charm, except this generator. How can I glean some more information about it with what I have, and/or is there something I am overlooking that might explain the problem?
Thank you so much for your help.
Best Answer
Re schematic, sometimes it takes time for the images to show up I guess, and I didn't see a reference to it in the text.
Have you measured the AC voltages to see if the transistor is producing any noise? Multimeter on AC range, most are AC coupled so on a 200mV range you can see 100uV noise for 3.5 digits and 10uV for 4.5 digits basic multimeter.
You are using an ugly bias scheme for T3 (why not Q3?)- it's beta dependent.
If you can't improve it, then adjust R21 so the voltage at the collector of T3 is where it should be (looks like about +1V would put it in the middle of the available swing).