Power supply problem

Hi everyone,

I’m building my shruthi-1 and I’ve already built the power supply, but when I check the voltages I get 1 and -1 instead of 5 and -5.

I’ve checked the polarities twice and It’s all ok and I’m putting the multimeter in the same position as in the photos, my regulated power supply (http://www.engelaxil.com/en/terrestrial-tv/indoormast-amplification/power-adapter-500-ma) it’s on 9v and center pin positive, so I don’t know what’s wrong.

I don’t know nothing of electronics so scuse me if the cause is that I made a very stupid error.

Thank you.

Read this ; in particular, please post the 6 voltages reading at each pin of the regulators.

7805:
O: 1
-: 0,01 (starts higher and goes down gradadually)
I: 1

7905:
O: -1
-: -1
I: 0`01 (starts higher and goes down gradadually)

And pin 5 of the LT1054 it`s on -1

Are you shure your Multimeter is set correctly for measuring Voltages??? It should be set to “VDC”, “V=”, “DC=” whatever is imprinted and a range of 20 Volts. Have a look into the Manual or take a look here and here

The multimeter has imprinted “DCV” and its pointing the “20”, it looks almost the same as the one in the photo of the building guide.

And it’s working with an almost new battery (used only to test the simple kits I purchased before starting the shruthi)

What puzzles me is that it either shows 1 or 0 - 1 is normally “out of Range”. Please try measuring a working Battery just to compare the readings (no matter 1,5V 9V… whatever you have at hand)

With an 1`5 battery and in the same position I mentioned before it says: 1…

Time to buy a new multimeter?

Can you post a Pic of your Multimeter please? Maybe you have something plugged in wrong…

It takes the concept of “digital multimeter” to a whole new level :slight_smile:

Yay - “Now with 1-Bit resolution for clear decisions.”

I’ve plugged the red probe in the other possible hole and the values don’t change wherever I put the probe

OK… i have a similar one with slightly different Print (came with all the Pots i ordered for free :wink: ) so maybe its time to get another working one if DCV 20 doesn’t work…

On your photo, the red probe is plugged in the right hole for voltage, resistance and small current measurements (the useful stuff unless you are repairing washing machines). Maybe the battery is kaput?

Personally, with thisi finr Quality Tool id refuse to touch anything that has more than 9-12V Potetntial. Even Eurorack Gear could be dangerous :wink:

New multimeter, new surprises:

PS at 7’5v:
4’3 and -4’1
7805: 4’3, 0, 0
7905: -4’1, -9’1, 0

PS at 9v:
6’1 and -5’8
7805: 6’1, 0, 0
7905: -5’8, -10’8, 0

I fell so special…

What I’m supposed to do now?

DON’T PANIC! (In big friendly letters…)

First, i cant understand you measurements at the PSU. If you Put the Black Probe to the outer Ring and the Red one into the Plug you can only read ONE VALUE, right? Whats the 2nd Value for? Or are these first readings with the Black Probe to GND and then measureing the positve +5V and negative -5V Rail?

Ok, but after don’t panic? xD

This one says 1’54 to a 1’5v battery, so it’s not as crazy as the other.

Thats perfectly OK. The reading depend a bit on the internal Battery Status for most cheaper Multimeters, so 1,54V means your battery is superok. What puzzles me is that the Voltage from the regulators is a bit high, it could be because there is no suifiicient Load to the Regulators. Try a 1K Resistor between the Positve / Negative Rail and GND an measure again. You then should be somewhere near the desired 5V.

If you don’t explain that in a “for dummies” mode I’m afraid I won’t understand it.

Continuing the assembly and expecting to get the correct values after the resistors steps?

Its the same as with the Motor in your Car: if you are in Neutral it reacts rather fast and with more RPM/Gas than while driving as the Car is a Load to the Motor. Same here with the 7805 and 7905 regulators. So put a resistor (say 1k or R470 or even R220) between the Power Rail and GND. You may simply stick it into one of the (hopefully) yet unpopulates Sockets. The Building Instructions show you the right Spots. With this load the regulator should show the correct Voltage and you can go on and proceed.