Voodoo Main Discussion

[Qiaozhi]

By the way, the voltage on pin 2 of U8 (LT1054) needs to be measured with reference to the -ve side of the battery. Note that U8 pin 3 is connected to -VB.

I've just done some measurements here on my working unit:
+5.03V at TP15
+9.07V on cathode of D6
+9.01V at pin 2 of U8 (LT1054) referenced to -VB.

This is becoming a mystery.

[waltr]

Sounds like the 78L05 to shutting down with load when all chips are in.
Since you did swap out the 78L05 (U7) this is a mystery.

Maybe try a different brand 78L05, they are not made all the same.

On the pre-amp there are series R's, 27 Ohm, R17 & R32. With the pre-amp in measure the Voltage drop and calculate the current draw. Should be less than 10mA. Too bad the other op-amps don't have a series R on their power to measure current draw.

The other circuits that use +5 are the level shifters, Q7, Q4 & Q8 but these have 10K Ohm to +5. Do check for shorts.

So what every the drain is, it's down stream of U9/U10. I am eyeing R34 or R28, I think. Hard to read Fig 3-12.

Yes, and lift one end of R35 & R33 to disconnect Filter outputs from PIC input.


Last, it could be a bad cap. These are hard to find.

[dingbatca]

Thanks for the good feed back. Now I have more to check. :-)

If U7 is a crappy... Would it be safe to connect my shop power supply 0V, -5V, +5V, up to TP1, TP14, TP15? Just as a simple test to see if everything powers up? I understand that if I built the board wrong, said test will release the magic smoke.

[Qiaozhi]

Thanks for the good feed back. Now I have more to check. :-)

If U7 is a crappy... Would it be safe to connect my shop power supply 0V, -5V, +5V, up to TP1, TP14, TP15? Just as a simple test to see if everything powers up? I understand that if I built the board wrong, said test will release the magic smoke.

You could remove U7, and then connect an external +5V supply between TP15 and TP1. If your power supply has a current limit control, you should turn that down to prevent any magic smoke being released.

The 78L05 regulators are rated at 100mA, which is more than enough to power the Voodoo circuits. It would probably be worth testing one of the devices you have with a variable load to see how much current can be extracted before it drops out.

[MartinB]

Thanks for the good feed back. Now I have more to check. :-)

If U7 is a crappy... Would it be safe to connect my shop power supply 0V, -5V, +5V, up to TP1, TP14, TP15? Just as a simple test to see if everything powers up? I understand that if I built the board wrong, said test will release the magic smoke.

.
Hi Dingbatca
Taking a simplistic approach, I would pull the IC's and then reinsert them in line with Georges build instructions given in Post #277 (copied below)
You will then stand a chance of finding with part of your build is not working.

1. Install the PIC and program it with the hex code from post #1. You need to have the PIC working, otherwise there will be no +5V supply. This is because the oscillator for the voltage converter comes from the PIC.
2. Install the transmitter circuit and test that it's functional.
3. It would probably be worth connecting the LCD and menu buttons at this stage, and flipping the detector into PI mode.
4. Build the PI preamp and check that the detector is working as a PI with a mono coil.
5. Proceed to build the rest of the PI channel and the audio amp. At this point you should have a working PI detector.
6. Build the DISC preamp.
7. Connect a concentric coil and test the DISC preamp output.
8. Flip detector into Hybrid mode, and build the DISC channel. You should now be able to test the hybrid capability.

Refer to page 31 of the book for the relevant waveforms.

[dingbatca]

I did build this board in stages, and tested as I went. Lets just go back to the basics.

TP2 & TP3 wave form. Per page 31 of the book, I should see a drop of about 20us, but I am getting closer to 224us? Pic attached.

[waltr]

I did build this board in stages, and tested as I went. Lets just go back to the basics.

TP2 & TP3 wave form. Per page 31 of the book, I should see a drop of about 20us, but I am getting closer to 224us? Pic attached.

The "drop" on TP3 is when the pre-amp is saturated. If it was coming out of saturation in 20us before then check the clamping diodes, D2, D3.
Also recheck the offset adjustment (R30) and look at TP5 to see if it is first or second pre-amp stage. Are the PL7, PL8 jumpers correct?

Also take a look at TX coil and ensure Damping resistor is still doing its job.

[dingbatca]

Thanks for the notes Waltr. I was able to track down the problem to the coil. The DXF coil has been giving me all sorts of problems. I used George's description for a "small concentric coil" (Pg 73) and it's seem to be working, and I am getting the same numbers as the examples in the book!!! Now I can do proper debugging.

[Qiaozhi]

Thanks for the notes Waltr. I was able to track down the problem to the coil. The DXF coil has been giving me all sorts of problems. I used George's description for a "small concentric coil" (Pg 73) and it's seem to be working, and I am getting the same numbers as the examples in the book!!! Now I can do proper debugging.

Carl has noticed a small bug in the menu system where it is supposed to restrict the disc sample from going over 100us. Unfortunately it was changing the main sample instead. Software Version 1.2 fixes this issue. The updated project and hex file can be found in post #1.

[MartinB]

I did build this board in stages, and tested as I went. Lets just go back to the basics.

TP2 & TP3 wave form. Per page 31 of the book, I should see a drop of about 20us, but I am getting closer to 224us? Pic attached.

Thanks for sharing. It is always good to learn.

[dingbatca]

I got my +5V back!!!

Just wanted to give a quick update. 78L05 is now in a bread board and hooked back to the Voodoo via leads. I measured 22ma across the output (with all IC's installed). When I remove U9, or U10, it drops to 12~13ma, but I get my +5V rail back. So for fun I moved over to a known good 7805 (1A capable). I now have all the IC's installed AND +5V! current draw is ~23ma. I am now 98% convinced I got a cheap counterfeit part from Tayda. That was a pain in the.....

[billr]

Yup. I can relate. Really chaps my butt going round in circles only to discover a defective part was the culprit.
Glad it's all good now.

[waltr]

Great news you got the +5 back. Yep, been there with bad parts.

[Qiaozhi]

I got my +5V back!!!

Just wanted to give a quick update. 78L05 is now in a bread board and hooked back to the Voodoo via leads. I measured 22ma across the output (with all IC's installed). When I remove U9, or U10, it drops to 12~13ma, but I get my +5V rail back. So for fun I moved over to a known good 7805 (1A capable). I now have all the IC's installed AND +5V! current draw is ~23ma. I am now 98% convinced I got a cheap counterfeit part from Tayda. That was a pain in the.....

That's good news, and thanks for coming back with the results. Quite often people just say that they've fixed the problem and leave everyone guessing what was wrong.
So the 78L05s you have are not up to scratch. They should be able to supply 100mA.

[dingbatca]

I will always do my best to report back, so others may learn from my failures.

I moved an 8lb sledge hammer over the coil and it detected iron.
I moved an aluminum plate over the coil and it detected non-iron.

I am ECSTATIC! Now I have a ton of work to get a proper coil up and running. But the circuit basics are up and running. I am thrilled.