Author Topic: Total Recall voltages  (Read 1293 times)

Jebus

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Total Recall voltages
« on: April 07, 2016, 05:55:22 AM »
Hello!

I finally got my Total Recall wired up and I'm bit confused with the voltages. I'm using the recommended EHX power supply. It reads about -31V (no load). I plugged it in and measured the voltage output from the LM7915 and it reads -18,3V. That feels way too high to me, but I cant figure out whats wrong.

Input of the regulator is about -29,6V and the regulator is grounded properly. Only thing I can think of is a bad regulator, but I don't have another one to test with. Any other ideas? :-\

midwayfair

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Re: Total Recall voltages
« Reply #1 on: April 07, 2016, 06:53:06 AM »
Measure something else, like another known working pedal with a power supply you're familiar with. Are the voltages high there, too?
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Jebus

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Re: Total Recall voltages
« Reply #2 on: April 07, 2016, 07:45:30 AM »
Measure something else, like another known working pedal with a power supply you're familiar with. Are the voltages high there, too?

Oh, forgot to mention: I tested it with two different multimeters and got same results. Also measured my 1Spot with both multimeters and it gave out 9,3V like always..

LaceSensor

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Re: Total Recall voltages
« Reply #3 on: April 07, 2016, 10:54:22 AM »
take all the IC out

test the power and gnd at the appropriate pin on each socket

test the power at the junction of the 10r and 240r power resistors
test power either side of the zener


Jebus

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Re: Total Recall voltages
« Reply #4 on: April 07, 2016, 12:09:35 PM »
take all the IC out

test the power and gnd at the appropriate pin on each socket

test the power at the junction of the 10r and 240r power resistors
test power either side of the zener

Oh, another thing I forgot to mention: no ICs attached yet.

I'll measure the voltages and report back.

Jebus

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Re: Total Recall voltages
« Reply #5 on: April 07, 2016, 01:22:44 PM »
no ICs attached yet.

And this was the problem. I didn't know this type of regulators need a current flow through them for the output to be regulated. I started thinking this might be the case and  attached IC1. Output of the regulator went to -14,9V. Attached rest of the opamps and its still happily sitting at the same voltage. :)

Thanks for the help!

alanp

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Re: Total Recall voltages
« Reply #6 on: April 07, 2016, 08:24:51 PM »
78xx and 79xx need loads, yeah :) That's tripped up a few people!
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