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PostPosted: Sat Jun 17, 2017 3:32 pm 
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Hi everyone,

I got a new-old-stock Reverb 2 pedal kit. It comes with v1.2 parts (e.g. C10k pot and R7 = 15k). It comes with a v1.1 PCB (i.e R7 labeled as 10k).

Symptoms are the same whether on battery or 9V regulated wall wart.
Bypass feature works and sounds fine.
After switching, there's no signal, no LED.

I've a fair bit of experience with electronics, so I've started stripping it down to reduce complexity and isolate the problem, but no luck so far.

I removed the BTDR-2H.
I've taken off all the caps (in case of failed short caps)
I replaced the diode (1n4001 -> 1n4003 from the bits box)
I replaced the LED with a spare
I've removed the 5V reg and the opamps
I've reflowed every single solder joint
I've tried 2 different power input jacks
I've tried both battery and PSU
I've tried totally disconnecting PSU wires and bridging the "+" connectors to run solely off battery.

Basically I'm left with resistors, the stomp switch and the LED. And it still doesn't work!

I get 9V across "+" and "-" power terminals.
I get 9V across the 78L05's input pin and "-" terminal.

Something curious: when I measure voltage across 78L05 input pin and ground I see 9V (expected), but I also see 9V across the 78L05's middle pin (GND) and the "-" input terminal! I would expect the 78L05's middle pin to be tied to ground in order for it to function. Is this normal?

Pics:
Image

Image

Help!!! What should I check next?? Thanks in advance.


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PostPosted: Sat Jun 17, 2017 7:53 pm 
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Is the schematic correct? For example, when I look at the schematic it's pretty clear that the LED power goes from +ve rail through a 4k7 through the switch to ground.

However, there is no connection to ground for the LED on my board. It literally has no connectivity to ground. :?: :?: :?:


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PostPosted: Sat Jun 17, 2017 8:08 pm 
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Yes, the schematic is correct.

I don't understand what you're trying to accomplish with the removal of the components. The effect will certainly not work with these components removed. Am I misunderstanding what you're trying to do here??

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PostPosted: Sat Jun 17, 2017 8:12 pm 
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duhvoodooman wrote:
Yes, the schematic is correct.

I don't understand what you're trying to accomplish with the removal of the components. The effect will certainly not work with these components removed. Am I misunderstanding what you're trying to do here??


The idea behind removing the components is to reduce the circuit to as simple a form as possible; first I want to just make the LED work. Once that works, I'll think about making the audio circuitry work!

For now I cannot even get the LED to light up.

If the schematic is indeed correct, then I'm more puzzled than ever because neither the LED nor the 78L05 are referenced to ground on my PCB, but instead to 1/2V. The schematic clearly shown the LED and 78L05 referenced to GND. On my v1.1 PCB 1/2V is taken at the junction of the 10k/10k voltage divider; this forms "ground" reference.


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PostPosted: Sat Jun 17, 2017 8:23 pm 
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Well that's interesting. If I add a link between the "-" terminal and the 1/2V point of the 10k/10k voltage divider, it works. The LED turns on/off with the switch and the opamps suddenly get power.


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PostPosted: Sat Jun 17, 2017 8:48 pm 
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And now having re-populated the board, it works ONLY if I join "-" to the GND junction of the 10k/10k resistor divider. I get the LED turning on, the opamps get ~ 9VDC, and the 78L05 outputs 5V. WTF.


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PostPosted: Sat Jun 17, 2017 9:02 pm 
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The circuit path for the LED is as follows: V+ to 4.7K current-limiting resistor to LED anode to LED cathode to footswitch lug 1. Lug 2 of the footswitch is the ground connection, so when the footswitch is engaged, it completes the path to ground and lights the LED. And the F/S lug 2 definitely connects to ground, not the 1/2V trace. The center leg of the 5V voltage regulator connects to that same ground trace. Any chance that your ground trace that runs around the perimeter of the solder side of the board has a break in it somewhere? Is the ring "finger" of the input jack making good contact with the sleeve of the input cable plug?

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My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2


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PostPosted: Sat Jun 17, 2017 10:06 pm 
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It must've been a break because I added all the components back, bridged that trace to GND, and now everything works. This things sounds FANTASTIC with just my Strat into the reverb into a Vox AC4C1 :) :)


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PostPosted: Sun Jun 18, 2017 2:20 am 
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This is the link I added to make it work:

Image

I've been playing it for hours, seems great. Very happy.


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PostPosted: Sun Jun 18, 2017 12:03 pm 
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Have you been powering the pedal from a battery or a wall wart?

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“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2


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PostPosted: Sun Jun 18, 2017 10:24 pm 
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duhvoodooman wrote:
Have you been powering the pedal from a battery or a wall wart?


Both. Same result.


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