Voodoo detector problem power supply

[nandimonay3]

I have a problem on power supply (voodoo m?tal detector)
+5 v on tp15 is missing
The pic is programmed with latest firmware 1.2
I made four motherboard and same problem +5v is missing on tp15
-5v on tp14 good
Help me plz







https://www.youtube.com/watch?v=7kDyrzC3qz4

[Qiaozhi]

What voltage do you have at the cathode of D6? You should read something like +11.7V. If not, then the LT1054 is probably faulty.
If the voltage is OK, then something is loading the +5V line.

The next step would be to remove some of the load on the +5V line by removing some of the filter ICs and check if the +5V line comes alive.

If this happens, measure the current consumption on the +5V line. Disconnect the output pin of U7 (78L05) and insert a current meter in the line. U7 should be capable of supplying 100mA before dropping out. If it cannot manage that value then the 78L05 is either fake or a sub-standard part.

[nandimonay3]

thank you for replying
I will try what you told me
and I will let you know what I got

[andon80]

hi, for it to be +5V, software must be installed in the processor, then it will work properly and you can see +5V

[yatahaze323]

Hi George,

I'm running into the same issue not having +5v line on two different boards. My cathode line on D6 matches what you wrote +11.73v on both boards. Also I used the LT1054 in my minipulses and had no issues with them in there.

I decided to remove U3 and my +5v line started working, I tried the same thing on the other board and the +5v line started working on that as well. I tried 4 different NE5532 to see if it had the same affect and it no matter which NE5532 was installed the +5v line would not work.

I also used these NE5532's in my minipulses that I built with no issues. Are these NE5532's bad? Or could there be something else causing this that I should check?

I did a bit more testing and the +5v line disappears when pins 5 and 6 on U3 are connected to the board.

Thanks!

[Qiaozhi]

Hi George,

I'm running into the same issue not having +5v line on two different boards. My cathode line on D6 matches what you wrote +11.73v on both boards. Also I used the LT1054 in my minipulses and had no issues with them in there.

I decided to remove U3 and my +5v line started working, I tried the same thing on the other board and the +5v line started working on that as well. I tried 4 different NE5532 to see if it had the same affect and it no matter which NE5532 was installed the +5v line would not work.

I also used these NE5532's in my minipulses that I built with no issues. Are these NE5532's bad? Or could there be something else causing this that I should check?

I did a bit more testing and the +5v line disappears when pins 5 and 6 on U3 are connected to the board.

Thanks!

The fact that the +5V line recovers when you remove some loading from the supply line, seems to imply that the 78L05 is not capable to supplying the required current. Have you tried removing any of the other ICs instead of U3, such as U1, U9, or U10?
Also, have you tried to measure how much current is being consumed, and whether it is close to 100mA?

What are your jumper settings for PL7 and PL8?

[Olly]

I'm not sure whether it's pertinent to this board or not but it's fairly common for regulators in a dual supply such as this one to have one of the regulators go into latch-up especially if the other regulator comes up earlier. In this instance the -ve regulator comes up first which will give an amount of back feed to the +ve regulator via the Op-Amp and could cause it to latch up. The normal method to correct or prevent this is to fit two protection diodes across the output of each regulator and its GND pin. With the +ve regulator (78L05) its diode's Cathode would go to the output and with the -ve regulator (79L05) the Cathode would go to GND.

Not all regulators are prone to this problem but the larger TO-220 7805/7905 are particularly susceptible. Not sure about these smaller 78L05/79L05 but I would fit the protection diodes to check.

[Olly]

Apologies my wording is a bit ambiguous. Two protection diodes are needed in total, one across each regulator.

[Qiaozhi]

I'm not sure whether it's pertinent to this board or not but it's fairly common for regulators in a dual supply such as this one to have one of the regulators go into latch-up especially if the other regulator comes up earlier. In this instance the -ve regulator comes up first which will give an amount of back feed to the +ve regulator via the Op-Amp and could cause it to latch up. The normal method to correct or prevent this is to fit two protection diodes across the output of each regulator and its GND pin. With the +ve regulator (78L05) its diode's Cathode would go to the output and with the -ve regulator (79L05) the Cathode would go to GND.

Not all regulators are prone to this problem but the larger TO-220 7805/7905 are particularly susceptible. Not sure about these smaller 78L05/79L05 but I would fit the protection diodes to check.

Could be worth a try ... although personally I've not had any issues with the boards I've built, or any of the [many] previous variants.
If there is a latch-up problem, it may only be happening with regulators from certain manufacturers.

[Qiaozhi]

It appears that earlier versions of the 78XX regulators were prone to this latch-up problem, and the datasheet recommended adding a reverse-biased diode across the output terminals. In newer datasheets there is no mention of latch-up issues.

My suspicion is that this may only be happening in cases where old stock or low quality parts are being used.

yatahaze323 - Can you please add a reverse-biased diode across the output of U7 (78L05) and report back as to whether the problem goes away?
I am unable to check this myself as the circuit is working perfectly without the diode.

Latch-Up White Paper - Texas Instruments

[yatahaze323]

I just read through everyone's replies, I just wanted to mention that I'm building the arduino variant in case its the arduino that could be causing this.

I installed U3 back into the board. I found that if I removed U9 or U10 that +5 will work.

The PL7 Jumper is connecting Pins 2 and 3, PL8 jumper is connecting Pins 1 and 2.

I will take some time tomorrow to try and add a reverse-based diode accross U7.

Thank you!

[Qiaozhi]

... I just wanted to mention that I'm building the arduino variant in case its the arduino that could be causing this.

This is unlikely to be the problem. There is no issue with the +5V supply on my Arduino Voodoo board.

[yatahaze323]

Ok so I only had 1n4148 or mur460 diodes so I used the 4148.

For the reversed biased diode I connected the anode side to pin 1 and cathode side to pin 3 of the 7805, was that correct?

TP15 now reads +8.13v with all the ICs installed. So the positive line now works but is not +5v.

[Carl-NC]

Ok so I only had 1n4148 or mur460 diodes so I used the 4148.

For the reversed biased diode I connected the anode side to pin 1 and cathode side to pin 3 of the 7805, was that correct?

TP15 now reads +8.13v with all the ICs installed. So the positive line now works but is not +5v.

It sounds like you have the diode backward. Are you using a 7805 or a 78L05? The pinouts are different.

[Olly]

78L05 Pinout

It must be Anode to GND and Cathode to the +5V Output.
For the 78L05 Pin 2 is GND and Pin 1 is the +5V Output.
Have a look at the attached datasheet.
lm78l.pdf

Cheers