Forum Vibe —> no oscillation

[lezerec]

I just built my Forum Vibe, and the LFO isn't oscillating. Well, it's the FV 5 in a standard version. The bulb is glowing, bypass is ok. The LFO LED is not glowing.
Here are my voltages (E, B, C) :

Q1 2,03 / 0,85 / 0,94
Q2 4,06 / 2,04 / 1,46
Q3 10,73 / 4,07 / 3,52
Q4 14,41 / 4,08 / 4,13
Q5 10,82 / 4,12 / 3,52
Q6 14,42 / 4,10 / 4,16
Q7 10,82 / 4,16 / 3,56
Q8 14,41 / 4,10 / 4,15
Q9 10,81 / 4,15 / 3,5
Q10 14,42 / 5,18 / 5,24
Q11 18,12 / 10,65 / 0
Q12 18,12 / 18,12 / 18,12
Q14 11,98 / 7,09 / 6,53

I think there is a problem with at least Q1, Q6, Q8, Q10, Q11 and Q12. But I am not able to understand from where it comes.

(I'm french)

Thanks a lot if you have time for me !

[Kipper4]

Hi and welcome.

https://www.diystompboxes.com/smfforum/index.php?topic=29816.0

We're probably going to need more info to help you better.

A schematic and probably some board photos for the eagle eyed.

Don't worry about the French thing.
I don't think anyone is going to hold it against you. Lol.
There's quite a few French speakers here.

Have fun.
Rich

[lezerec]

Thanks a lot

Here is a link : https://www.classicamplification.net/fv/FV5_BuildLayout.pdf
Mine is the FV5 vintage style with 2N trannies

Here are some pics :







The pots are presumed hooked up fine. I've got a working Univibe I built 1 year ago, so I have been able to compare. All components are presumed the same in the good orientation or polarity. All connections are presumed to be done well.

The only difference : the pedal is integrated into a homebuilt pedalboard. Working well too.

I'm fed up

[willienillie]

There is an error in the documentation.  R48 and R49 need to be swapped.

[lezerec]

You mean R48= 100k instead of 47 k , and R49=47k instead of 100k ?

[willienillie]

yes.  oui.

[lezerec]

Hmm sorry, I don't think so : my other FV5 is working fine when R48 and R49 are not swapped.. according to the schematic and the lay out, it seems correct

[willienillie]

]It might work either way, my experience was complicated by the fact that I used a trimmer there.  But they are reversed on the layout, unless it's been recently corrected.

----------

Let me expand a little on this.  The schematic you posted above also has an error, which makes things more confusing.  It uses the designators R47 and R48, for what are on the layout R48 and R49, respectively.

Here is another schematic, also from Classic Amplification, that properly corresponds to the layout:



Again, this might not be related to your LFO not working at all.  But in my experience, the pedal works better with the correct R48 and R49 values.

[lezerec]

Ok, thanks for that ! I will try and must find why it's not working

[Kipper4]

Thanks a lot

Here is a link : https://www.classicamplification.net/fv/FV5_BuildLayout.pdf
Mine is the FV5 vintage style with 2N trannies

Q11 Q12 form the lfo
Q13 is a buffer/amp

Your Q12 voltages look funky.
I'd focus on that area of the circuit.
Q12 should have a varying voltage.

Is t1 set up correctly?

You got this mate. What do the voltages say on your working unit?

[lezerec]

- Are you talking about powering the Vibe ? It's 18 V

- I swapped r48 and r49, it doesn't work much more.

- I should try to set up T1 while playing guitar. Actually, I haven't done it because I should have heard a bit of vibe whatever position it was.. Maybe that's a mistake, Let's try !

Please note that the LFO Led is not working. As you said, the issue is in the LFO section. I just ordered some new 2n5088 and 1uf capacitors..