Dirtbag no Modulation

[marmaliser]

So when I built my MN3005 Dirtbag at 15v  and it fired up first time and I  got it biased up pretty easily I was over the moon.  After a day or so I realised I had had no modulation at all .

The only sub I can think of that might have affected it is CD4047ube for  CD4047BCN

When playing if  i turn the modulation pot I get that modulation noise with the pitch changing like you would expect when turning the pot.  Also when flicking the switch I also get a pitch warble.  But after that no modulation whatsoever

I have checked all values around the Mod section

Any ideas guys?

[madbean]

You say you get pitch changing and warble. That's what the modulation is. The knob should increase the intensity of the effect as you turn it up. Does it stop working as you turn it up? I'm a little unclear.

[marmaliser]

I only get a warble as I turn the pot.  You know like when you turns pots on a delay/chorus whilst playing you get all kinds of crazy sounds.

With the pot static in any position I get no modulation at all

[madbean]

Ah okay! Now I understand. This could mean the LFO is not working for some reason. You could still get some warble adjusting the pot this way.

Hmm...well, let's have some voltages off the pins on IC7. The voltages on pins 6 and 7 should vary slightly.

[marmaliser]

Thanks Brian, didn't explain it very well initially.

Just took voltages and they looked way of compared to another thread so I had another look around ic7 and then decided to swap it out to discover that pin 2 had been bent under when inserting.. Bugger !!!

IT WORKS PERFECT - I AM SO HAPPY

Thanks Brian (that's genuine thanks not in a "Thanks Ken" Kind of away lol )

Build report to follow

[madbean]

It's funny because when I initially built up my own D-Bag, I did the exact same thing---bent one of the IC pins on the modulation chip.