diy univibe no sound

[plen]

about 6 years ago my son and i built a diy univibe each. the both worked buy his was better than mine. my one was not very loud. i didnt bother about it till a couple of months ago. i had taken a few parts from it for other pedals. i put the parts back, but there was no sound. i took all the transistors capacitors out and measured them. they all seem alright. i measured all the resistors in circuit and they all read the same as my sons working one. i took his board out of his and tried it in my enclosure and it worked so it is something on my board thats not working. it is only the sound not working as the lights flash. i cant think of anything else to check. anybody any ideas.

[Kipper4]

Welcome.
6 years ago. Wow.
Help us to help you please show us the schematic you are working from.
Go here
https://www.diystompboxes.com/smfforum/index.php?topic=29816.0
Report back with some more information to aid debugging.
Looks like the lfo is working if the bulb is flashing.
Do you own an audio probe? Worth a search if you don't and it might come in handy later on.
Could be a multitude of things, curious that yours was never as loud as your sons too.
Let's see what we can find. Respect to anyone who can build a univibe.

[plen]

kipper4 thanks for the reply here is the layout i used. i hope it is ok to use it.

[Marcos - Munky]

Post a few photos of the board. Also, do you have a multimeter and do you know how to do an audio probe test?

[plen]

marcus - munky i have got a multi meter. here are some photos.

[Marcos - Munky]

Nice pics, and very nice looking board. This seems to be a clone of the original univibe board. Post a photo of the trace side, maybe we spot something you didn't.

Also, which transistors did you used? And how are you powering it?

Since you have a multimeter, be ready to measure voltages of all the transistors but Q11, Q12 and Q13, since they're part of the lfo and we know they're working. Connect the black probe to ground and use the red probe to measure the voltages on each leg of the transistors. But first let us know the transistors used and how are you powering the circuit, maybe you don't need to do those measurements.

[plen]

transistors are all 2n5088 excepy the first one which is a silver bc109. i am powering it with 15v wall power supply. i am not sure of the order of the transistors. do they start with the silver as Q1 then go up the left then along the top then the ones in the middle.

[Marcos - Munky]

The layout you posted have them marked as Q1, Q2... until Q13.

I can't clearly see on your photos, but are the transistor legs twisted or something like that? Could you post a close-up photo of the transistors and how their legs are getting into the board?

[plen]

the base and collector pins are twisted.

[Marcos - Munky]

Yep, that's how they need to be connected. So, we'll really need the voltage measurements of all transistors (but the 3 from the lfo).

[plen]

i will do these as base collector  emmiter  Q1 1.109 1.566 .621    Q2 1.567 1.626 1.629    Q3 1.484 1.310 1.313   Q4 1.624 1.586 1.534   Q5 1.534 1.881 1.404    Q6 1.628 1.587 1.549   Q7 1.549 1.888 1.431   Q8 1.627 1.586 1.544   Q9 1.544 1.878 1.429   Q10 1.725 1.585 0000   Q11 1.616 1.517 1.452   Q12 1.448 1.517 1.441   Q13 754 753 107    i have done all 13.

[Marcos - Munky]

Your voltages are very low. I mean, Q1 is somewhat near what you should expect. On the collector, you should expect around 5V for Q2, 10.5V for Q3, 15V for Q4, Q6, Q8 and Q10, and 11.5V for Q5, Q7 and Q9.

The power supply part of the circuit is on the bottom right side of the board. Check voltages on power input (the one connected to D3) and at each + lug of those big caps (1000uF and the 2 220uF). All voltages again with the black probe connected to ground of the circuit.

[plen]

i tested the transistors in diode mode with no mains power was that right.

[Marcos - Munky]

No, you need to check their voltages, with the power plugged in.

Since you have a multimeter, be ready to measure voltages of all the transistors but Q11, Q12 and Q13, since they're part of the lfo and we know they're working. Connect the black probe to ground and use the red probe to measure the voltages on each leg of the transistors.

[plen]

i took the readings again with the meter in diode mode and power on.   Q1 1.015  1.759  623   Q2 1.758  1.315  1.633   Q3 1.958  0000  1.316  all the other transistors read zero.  the 3 large caps read zero. d3 diode reads zero.

[R.G.]

Don't use your meter in diode mode for this. Switch it to voltage measurement. Clip the negative/black lead of your meter to circuit ground. Use the red/positive lead to test voltages.

Here's what you're looking for. For NPN bipolar transistors (all the transistors in the univibe circuit are this kind) the base will always be 0.5 to 0.7V more positive than the emitter terminal. If this is not true, then the transistor is not working as an amplifier. The collector terminal of the transistor must  be more positive than the base* by one to many volts for the transistor to be working as an amplifier.

Before you get too far, re-re-re-check that all of your transistors leads are in the circuit-correct holes. When you have to twist leads (I think in this case you had to reverse base and emitter) it is easy to miss one. It's also very easy to have the two leads short together. Once you've done that, measure the voltages on the solder pads of the transistors, as it's easy for a meter lead to be mis-placed. Ask me how I know this. 

Make us up a chart of the transistors by number, and the voltages on each of the terminals. For this test, the DC power should be on, and there should be no signal. I've done a lot of troubleshooting on the univibe circuit, and I can often spot what part is wrong from these voltages.

*[This is generally true, and true for all of the ones in the univibe. There are a few exceptions, but don't confuse yourself with the exceptions until you understand transistors better.]

[plen]

base collector emitter  Q1  .065  .638  .001  Q2 .636  .077 .072  Q3 15.56 .001 .001  Q4 5.00 15.56 4.57  Q5 4.57 11.49 3.95  Q6 4.92 15.56 4.49  Q7 4.49 11.60 3.87  Q8 5.24 15.56 5.29  Q9 4.82 11.45 4.20  Q10 6.30 15.56 5.79  Q11 920 18.56 9.90  Q12 9.40 18.56 9.90  Q13 2.993 12.94 2.358   diode d3 19.30   big capacitors 18.56  17.04  15.56

[Marcos - Munky]

Even without a chart as asked by R.G., I can see some things that clearly are wrong.

Around 15.5V at the end of the power suply. That's ok. Lfo working. Q4 up to Q10 have voltages very close to the expected values, we cay say those are ok.

Q1 voltage is very low. You should expect around 2V on the collector. The same goes for Q2, you should expect around 5V on the collector. Q3 is pretty odd, you should have around 10V on the collector (you have zero), 5V on the base (you have 15V!) and 4.5V on the emitter (you have zero).

So basically recheck all those resistors on the left side of the board. Check the layout you posted, they're all in orange. Visually check if they have the correct values. Check Q3 to see if the legs are at the correct places and if they aren't shorting together. Do the voltage measurements again for Q3.

[plen]

marcus munky i measured q1 q2 and q3 again Q1 base000 collector 14.40 emitter 66    Q2  the same as the last time i read it  Q3 base 000 collector 14.40 emitter 66

[Marcos - Munky]

So something is clearly wrong around those transistors. Check the resistors I said, you may have replaced a few of them for wrong value ones.