Weird Terminal 9 voltage on speedball + dead left channel [solved]

[FairDinkum]

Ok. I've cleaned the board up anyway and tested the components via the back of the PCB. The components look ok.

Not looking forward to the voltage checks but I guess it has to be done.

[FairDinkum]

I've put the PCB back after checking the soldering etc. No spars this time but unfortunately the same set of LEDs is still not lighting up. Should I attempt to replace them?

[Kris]

I'm not an expert here, but (per your last picture) it looks like small resistor is fried.
I hope PB can chime in soon to guide you a little further.

[Grainger49]

Nice catch!  Kris is right, that wide back band says it is toast.

[FairDinkum]

That's just the shadow from the flash I think. here's a better picture.

Edit: just measured the resistance of that resistor. It's giving me a reading. I presume that if it's blown I won't be able to get a reading.

[Grainger49]

I see a a small dark spot.  But to be sure throw a meter across it.  The manual will give you the resistance.

[FairDinkum]

I see a a small dark spot.  But to be sure throw a meter across it.  The manual will give you the resistance.

Oh my gosh the resistance is way off! It's not measuring 31.6 ohms at all! I'll replace the resistor tomorrow. Nice pick up!

[FairDinkum]

Alright just to clarify: I should shop for a 31.6 ohm 1/8 watt film resistor. Does it matter what tolerance it is or the manufacturer?

[Grainger49]

First lift one leg of the resistor to make the resistance check.  It is probably in parallel with something that will mess up the resistance you read.

Only one lead needs to be lifted, that takes it out of the circuit.

[FairDinkum]

First lift one leg of the resistor to make the resistance check.  It is probably in parallel with something that will mess up the resistance you read.

Only one lead needs to be lifted, that takes it out of the circuit.

I did exactly that and it's showing 320 kilo ohms when it should be 31.6 ohms.

Now I'll just have to go find a replacement and test it out! Thanks guys!

[Grainger49]

First verify the color code.  If it is correct according to the manual you need a replacement.  Bottlehead will send it or you can source it locally, maybe faster.

[Paul Birkeland]

I would measure the other 31.6 Ohm resistor to be sure your meter will measure it properly. 

[FairDinkum]

Thanks Paul. The other resistor is measuring 31.6 ohms on the dot. I hope that this is the main problem. As I recall, initially only one of the LEDs didn't light up, and I proceeded to reflow the center leg of the TIP-50, leading to sparks under the PCB which must have blown the resistor. Hopefully both LEDs will light up with the replacement of this resistor.

[Grainger49]

You are not reflowing with the Crack turned on, are you?  That is not a good idea.

[Doc B.]

Generally a resistor goes like that because it drew way too much current (during that spark, the source of which we don't know). So you have treated the symptom but not necessarily the cause of the symptom. I would follow PBs suggestion and check the resistance between each pair of pins on the transistors. Measure the resistance between each possible pairing of the three transistor leads on the 2N2222A and also check the TIP50 the same way. If you see a very low (under 100 ohms) reading across any pair the transistor is blown.