Harbinger One - Rate LED not flashing

[cooder]

Got it, I have the right one installed and still will not work.

The actual pot value would also not be a cause for this problem, it would just have a different feel to how the speed increases or decreases. The spread of range would be not so even with a normal log pot. It shouldn't have any effect on the LED flashing.

[Axeman]

I replaced Q11 and 12 and used a MPSA13 for Q13 and the light became brighter only, no pulsating.

[Axeman]

OK I replaced R46 and R47 to check if correct value and they are, replaced with checked new ones.  Replaced Q13 from 2n5088 MPSA13 and now my head hurts from the laud  buzzing sound.  When I short out the C22 1uf cap the LED turns on, if I rapidly adjust the gain the LED pulsates only one time.

What else

[Axeman]

Ok. I did a voltage reading on every transistor and they check within perimeters.  I also checked continuity, when I checked Q12 B and C the light appeared as if it wants to pulsate, the 2 transistors Q12 and 13 were replaced with new ones 2 weeks a go with some Fairchilds .


HELP

[madbean]

The LED1 not flashing is not going to be helped by changing Q11/Q12 or R46/R47. I've double checked the flashing circuit and it can indeed crap out at the slowest speeds, but this is fixed by using a 10uF in place of 1uF for C22. And, that's really the only change needed - leave all the parts stock as listed. You can brighten the LED up by reducing R54 to 470R or 330R.

So, we might need some pics of the top and bottom of your board specifically in that area of the circuit to see if there's something weird going on. Keep in mind that the flasher is basically a hack for a cool flashing light (and it's pretty much on/off and not ramp up and down in brightness) but not intrinsic to the operation of the vibe.

[Axeman]

Ok while I was taking some photos I shorted out  something on the board and the led turned on.

[Axeman]

Does Diode 4 and 5 have anything to do with the light pulsating?

[zgrav]

"The two diodes across the center capacitor limit the size of the LFO output waveform. An oddity of this particular way of building a Univibe is that the LFO amplitude goes up with increasing speed, even with the diodes there. "   This explanation is from the RG Keen article about the Univibe (http://www.geofex.com/Article_Folders/univibe/uvfrindx.htm ). 

[Axeman]

Thanks, but I have very slight understanding what the literature you refereed me to meant.   

[zgrav]

I know what you mean, but it is not often you can find a good article explaining what is happening in each part of an effect you are building, and it is an opportunity to put some time into understanding it since that will pay off in other projects where all you might have will be a circuit diagram.   The short answer to your question is yes those diodes are part of the flashing circuit.  They limit the range of the voltage that drives the flashing circuit to make the bulb glow brighter and dimmer. 

[Axeman]

Roger that. I figured they did based the schem.  I removed them and tested them they are good.  Installed some new one they also got tested.  So where I'm now is, signal goes through and when I apply an external flash light that blinks the pedal works.  I'm going to remove and test R41 through 46.

[zgrav]

I know from other forums posts on these builds that it can be tricky getting the flashing circuit to work.  at least you know that the filters and LDRs are working since your flashlight gets a reaction when you turn it on and off.

what voltage reading are you getting with a DMM at the bulb?  Also try turning your trim pot to each extreme and see if you get any kind of variation in the voltage at the bulb then.

[Axeman]

I hope the numbers and the arrows of the trim pots make sense

[zgrav]

I see the range of voltages you measured.  Now, if you put the trim pot for the flashing circuit minimum/middle/maximum and just measure the voltage at the bulb while the rate control is set to the slower part of its rotation, are you getting a fluctuating voltage for each setting?    (and my apologies if that is what is on your chart and I did not understand it).  Since it is an LED you only need something that falls below and then goes above the LED turn on point.   It may be that you have a fluctuating voltage going to the LED but it is either above or below that threshold.   

[Axeman]

The arrows on the image are the trim pots and the directions they are turned  and with the corresponding voltage.  I hope that makes sense