Why are my collectors stuck at 9v?

[Ben79]

I've been building an Os Mutantes. It doesn't work. Both my collectors are stuck at 9 volts - how can this be?

I've checked the resistance from the +9v power rail and they're both as they should be…HELP!

[crochambeau]

I've been building an Os Mutantes. It doesn't work. Both my collectors are stuck at 9 volts - how can this be?

My guess is that it's either wired incorrectly or stuffed with wrong parts (or orientations). To get a dropped voltage off the power rail, it needs to trickle to ground - for example, hang a 100K resistor off your 9 volt battery and if it's just flapping in the breeze you can measure the 9 volts (referenced to the negative battery terminal) on either side of the resistor - the voltage drop only occurs when current is flowing through circuit.

That's where your actives come in to play, if the transistor is not biased correctly and happens to NOT be a leaky piece of shit (sorry, I mean with vintage mojo, blah blah blah) it's possible it's just sitting there refusing to conduct, which would put you in the roughly Vcc on collector camp.

Might be able to narrow that down if provided with a picturesque view, but barring that my money's on biasing. Or assembly error, never rule that one out.

[crochambeau]

What's the base to emitter voltage look like?

[Ben79]

Thanks for your help!

Base to emitter on q1and q2 is 0


q1
c 9
b 6.8
e 8.6

q2

c 9
b 8.6
e 8.6

Components all checked and all good - I'm thinking a grounding issue might be afoot.

[Ben79]

Ok, it was grounding. I used a jack socket for the input that I pulled out of an old Traynor mixer and it turns out it's not a switcher, so the power and board grounds weren't connected.

Q1 looks good now but Q2 collector is at 0.17 volts and doesn't change when I alter its 5k collector trimmer! I think I must have wired the trimmer in wrong - it's a weird old one.

[Ben79]

The trimmer was busted! Replaced it.

Still doesn't work. This is becoming a debugging marathon and lesson in frustration management.

[crochambeau]

This is becoming a debugging marathon and lesson in frustration management.

Cheap education; just remember to breathe, hydrate and don't worry about taking breaks.