Rangefinder No Output

[bronomo]

Hi all,

I've recently completed a Rangefinder PCB and am having trouble getting any output. So far I've:

• measured and set the bias at -7v from collector to ground
• tried a handful of Russian germanium transistors in the hfe 70ish range with very low or unmeasurable leakage (atlas)
• swapped to a 2n5087 for testing to eliminate any weird germanium issues (?)
• probed various locations on the PCB to see where signal stops; it reaches the base of the transistor and no further
• measured all resistors on the board
• measured the pot make sure it wasn't shorting, both outer terminals are about 5kohms to the center terminal
• checked all cap values against the schematic
• measured the power out from the charge pump at -9v
• checked continuity from signal points (collector, capacitor, pot terminals) to ground to make sure it wasn't grounding out
• reflowed the socket and checked continuity from transistor leads to solder points on back of the board to make sure the socket isn't funky and they are seated properly

I feel like I'm missing something stupid and obvious because I'm not sure what else would be going on. I am using a LT1054 instead of a TC1044 but I was under the impression they are interchangeable?

 

[Feral Feline]

When you measured the resistors on the board, you mean they were already soldered on the board?

If so, you won't get accurate readings because in circuit they'll be interacting with other components in the circuit;
recommend a visual check of the colour-bands and make sure things didn't get mixed up ie reading the bands left to right or right to left, each of the following pairs has the same colours in the same order but are different values depending on which ordwer you read them:
120Ω vs 10k
130Ω vs 100k
1k2 vs 11k
1k5 vs 11M


That's all I've got as you've already exhausted anything else I could think of checking, and more!



My classic fail that scarred me for life taught me a good lesson was my copying a schematic and inadvertently putting "k" behind 390 when it should've been an "r" — I checked the circuit against the (copy-) schematic and it was "correct" — my friend spotted it right away: too much resistance, that transistor was never going to turn on.

Anyway, here's the bump for somebody else to come in who knows more than I and can hopefully find the fault. (Faulty board — hey it can happen! Not the layout, but the manufacturing process...

 

[bronomo]

I did measure the resistors in-circuit, I think maybe this one you get lucky that there's something that blocks DC in a way that isolates the leads so the only path is across the resistor? But noted for the future, it makes sense that wouldn't always work. I did verify them visually now and they match the schematic.

What I'm the most stumped about is that the signal makes it to the transistor base, and the transistor biases correctly, but there's no output on the collector? I think the probe I'm using (MAS Effects DIY pedal tower) has a cap built in so you can probe at points that have a DC bias (which I think makes sense because I'm getting signal at the base, which should have DC across it from the voltage divider?) I've tried with at least 4 different transistors (Ge and Si) and all are the same