Quick troubleshooting question for gravitation reverb

steviejr92

Member
Hey guys your friendly neighborhood noob here once again. I just have a quick question I’m measuring the forward voltage on my diode it’s a 1N5817 Schottky diode I read that it should have a forward voltage of .2 v when I measure I get .167 is this ok?
 
  • Like
Reactions: fig

mybud

Well-known member
Apparently you can blow up elcaps by connecting them backwards too. All this talk about magic smoke and burnt out components aside, trust your build works after all this. It’s such a groovy feeling when the little blighter fires up the first time and phasey, flangery, booster, what have you sounds emerge. And actually troubleshooting is a really good (sometimes inevitable) way to get familiar with the actual workings of the circuit.
 

EGRENIER

Well-known member
The circuit had these two 10Rs in series with the power for whatever reason and trust me they blew up. 😜

The -12V and +12V supplies were wired backwards in my haste to hear what the circuit sounded like. Not like much, as you can imagine.
That's weird, the only thing that I know that can burn a resistor is excessive current, the fact that you reverse the polarity should not be the cause...Oh well...
 

phi1

Well-known member
^ I was thinking maybe there was a 1n4001 from power to gnd after the 10R resistors. Then the diode fried and shorted, which drew excessive current through the resistors. If so that’d be a bad design. I’ve only ever seen the diode to gnd directly on the 9v input. Or maybe there wasn’t a protection diode and some other downstream component shorted power to gnd after the resistors. I could be wrong about what happened, I was also trying to make sense of it. But yeah, oh well. I think the pedalpcb way (not sure who started it on pedals) solves all the issues.
 

mybud

Well-known member
That's weird, the only thing that I know that can burn a resistor is excessive current, the fact that you reverse the polarity should not be the cause...Oh well...
Yes, by no means do I disagree with you, @phi1 and @EGRENIER.

What I was describing was the evidence (the effect of the reversed power), not the cause.

I surmise that the resistors blew because the reverse current was drawn so that a component designed for -12 was forced to operate at +12. As @phi1 said, '... some other downstream component shorted power to gnd after the resistors.' Maybe it was the 7805 which blew and sent reverse voltage to the rails though the 10Rs thereby*. The microprocessor died as well as you'd expect, so I ordered a replacement board and chip for later.

*I revisited the docs: "Power Supply: Here we see footprints for two different types of power connectors. The Positive and negative voltage rails go through 10 ohm resistors and are then filtered by 10uf caps, and .01uf caps on the pins of the op amp. The positive rail is then sent to a 7805 voltage regulator which provides +5V reference voltage for the microcontroller." The PSU section of the circuit contains no diodes.

I managed to build a successful replacement later

_ sound happy ending chord here_,

but most importantly I highly value your responses (and interest).

Thanks for taking the time and trouble to discuss this. I learn as I go and this was great food for thought about design quirks.
 
Top