Power problem

I’m building the 4-pole filter for Shruthi.
I soldered everything and checked no shorts without ICs in, as explained in the build instructions. Then I put the LT1054 and checked voltages but they were wrong - first about -2V, later 0V where it should be -5V . Then I noticed I misplaced 7805 with 7905 and vice versa.
I have unsoldered 7805 & 7905 and replaced LT1054 with another one. Now, power on without the regulators, I can read -1.8V on LT1054 pin 5. I guess it should be about -9V (my power supply is 9V battery). Or is it normal without the 7905 connected?
The LT1054 is getting very hot after half a minute or so.
What could be wrong?
The connections seem to be fine.

wojtek

You should be able to measure a negative voltage on pin 5 of the LT1054 (something around -8V) without the regulator.
And the LT1054 shouldn‘t get warm.
Check the orientation of the chip and the surrounding capacitors.

I have checked orientation of the LT and capacitors, all seem fine. All other connections also seem ok.
Could one of the capacitors be faulty and causing this?

Google Photos

did you etched pcb on your own?
if yes, did you do something to metalize holes? - it might be source of your problem :wink:

I have ordered the PCB and yes the holes are metalized. I have already built the control board and it works fine.

ah ok

Can I remove all the capacitors around and test without them? Then keep adding to see when it breaks.
Or are some absolutely necessary for the LT1054 to work?

31/5000

I think the LT1054 is broken. I would exchange it. Can you show us your schematics?

I have already replaced LT1054, the same issue, so if it’s also broken then something is breaking it and I need to find out what it is.

Can you show us your wiring diagram and PCB pcb. Greetings from Germany. Rolf

This is the power supply of the Shruthi filter. You can disconnect Pin5 from the board and connect another 10uF cap to ground. And than measure the voltage and temperature.

Thanks, yes, I have already done that (removed the regulators) and getting wrong voltages - see my earlier comments.

Did you test every pin wrong contact with other pin ?

Yes, there are no shorts there.

Ok, I have moved forward a bit. I have removed C1 and noticed LT1054 does not get hot any longer. I have put an electrolitic 10uF in place and still ok.
However, I’m getting only -3,5v at pin 5. I have checked with 9v battery and 12V power supply.
Is the IC damaged? I have two, getting the same with both.

I guess C1 had wrong polarity. Could it had broken both LT1054? I have used both in this broken setup.

Most likely.

Well, I have replaced 1054 with a new one. And still the same, -4 at output when there is 12v on input.
I have recreated the power supply on a breadboard and it’s the same!


It’s just the diode, 1054, c31, c32 and c35. The only difference is that c35 is 20pF instead of 10.
I’m measuring on the white wire, against input ground. It’s -4V. Input is 12V.
The two capacitors have correct polarity, + on right side, pin 2 of the IC.

  1. Is that a new tantalum or the same you had reversed? (That will be damaged)
  2. Try with both 100uF capacitors (C11 and C12 on the schematic posted in this thread)