not enough experience, or none at all!

[jhettel]

I have been putting off writing this message because I just do not know what to do. I received my 14 x 18 searchcoil blank from Hays yesterday and thought I was ready to go. I have very limited knowledge of electronics and have been trying to assemble my Hammerhead project. The directions are pretty simple and I am sure most people could do the project with just a little electronic knowledge. I did build the gradiometer from a kit I bought from Fat Quarters, and it does work, so I decided that if I could do that, then I can do this. I followed the directions meticulously and installed all of the components for the power section. I have checked and rechecked and all of my diodes, capacitors, IC's, (I used a socket on IC1) are installed correctly. Last time I went to the local electronic store, whose workers are very knowledgeable on electronics (this was not a Radio Shack) they looked at the circuit board and said that everything looked fine and that my soldering also looked pretty good. I used a heat sink on every component except for the IC socket, so I did not burn anything up that I know of. I also double checked my battery connector and the red wire which goes to the female connector of the battery terminal is on the switched side, so everything looks fine. Problem is that I am not getting the correct voltage at the test areas. I have numbered the pins to be sure and am getting battery voltage at both IC2 and IC3. I installed the jumper between the IC's and diodes but that did not help. My problem is that I have no idea of what I did wrong nor no idea of how to check the components. Maybe I bit off more than I could chew. If I cannot get it to the right voltage then I will probably just have to quit the project and maybe sell everything on e-bay. Hate to do that but I am frustrated to the point of giving up. The Hammerhead I am sure is a great pi detector, and would serve me well with the 18x14 searchcoil while searching for large civil war projectiles.

[Carl-NC]

So are you getting correct supply voltages? I.e, outputs of IC2, IC3, & IC4.

If you get really, really stuck, send me the board and I can troubleshoot it.

- Carl

[Joe Hettel]

Thanks

Thanks Carl for the offer. I will check it out thoroughly before I take that drastic of an offer. I really appreciate all of your help.

[jhettel]

Thanks for the offer Carl, that is really great of you to offer the help. I will check the board again and see if I can find the problem. Thanks again

[Reg]

Hi Joe,

Maybe if you tell us some of the TP readings and what you are using to read them, we can offer more ideas as to what is wrong. TP voltages are sort of tattle tales of what is happening.

Now, Carl is correct in the fact that first you need to check all power supply (PS) voltages to make sure they are correct. If the PS voltages are not correct, then most everything else will be wrong also. That is the first place to check. If they are ok, then you need to note all other readings and what might change them.

As an example, I would ignore the first three tp's for the time being and check TP 4 to see if that can be adjusted and is close to being in range. the scope is the best way to set this TP, but a meter will work also.

Next, check TP 5. This should be near 0V but as long as it is less than 4V, or close to that, the detector should work. This voltage probably should change if you increase your delay a lot if you are reading much of a voltage. TP 5 is a good indicator of what is wrong if the power supplies are working fine. It is a very good way to tell if you are sampling to soon.

Let us know what readings you are getting and what test equipment you are using.

Reg

[Unregistered]

Thanks for the help and the reply. So far I have not made it past the power supply section. When I checked the voltages in the power sectionthere most of them were the same as my battery voltage. So, I did not install any of the other components until I get the voltage right. I am using a digital meter. My battery voltage is 12.32 v. At IC2 pin 1 I have 12.28v. At IC3 pin 3 I have 7.36v. At IC4 pin 3 I have 7.34 v. and at IC2 pin 3 I have 12.32v. I have checked everything and the polarity on all of the capacitors is correct, the diodes are installed correctly, the jumper is installed, the IC1 is not installed backward and is installed in a socket, and the other IC's are installed in the correct direction. I have also checked all of the solder joints and none are bridged. I took it for granted the C4; C5; and C6 are 47 uf and not 22uf. All of the capacitors are also electrolytic. So I am scratching my head and wondering what to do. Your help is greatly appreciated, as is Carl's.

[Reg]

Ok, lets evaluate what you have posted and see what we can figure out.

First, always connect your black lead (the - input) of your digital voltmeter to the ground connection of the pc board. This keeps things consistent and makes the voltages match or try to match those indicated in the article. For simplicity, the ground will be any connection that connects to the outer large trace that goes almost around the entire pc board. Now, the digital will indicate either a positive or negative voltage depending upon what you are measuring.

Now, if you use the above connection for your negative lead of your meter, then you should get different voltage readings if your battery is connected properly. Remember the + lead of the battery is connected to the ground, so the input voltage on IC3 has to be the -bat voltage of -12.32V. The hole or pin if you have installed one, labled SW1 on the part layout is the ground pin.

So, check the battery voltage first to make sure it reads a -12.32V. This is the voltage at the hole labeled VB on the part layout pic. Now, the middle pin of IC3 should measure the same as your battery voltage, so it will measure a -12.32V also. If it is proper, then measure the other two pins on IC3 and see what they measure. One end pin should measure 0V since it is connected to the ground. The other end pin should measure a -5V. If you do not measure a -5V or very close to it on the other end (the other IC outer pin) pin, then check carefully check the IC number on the IC to make sure it is a 79L05. It is possible that you have the wrong IC number or maybe a bad IC.

Let me know what you find out. Once we get the -5V correct, well will get the other voltage going.

Reg

[Reg]

After reading again what you wrote and then what I wrote, I am thinking that your unit might be working ok and the problem is simply a matter of how you connected the voltmeter.

If you keep the - input of the voltmeter always connected to the ground, then your voltages just might be correct on IC3. You did measure 7.3 volts at the output of IC 3, which might indicate that you had the - input of the meter connected to the - of the battery, rather than the + output. If you did this, then you would read about 7.3V at the output of IC3.

Reg

[Carl-NC]

I agree with Reg, at least for IC3 & IC4. Sounds like you don't have your black lead on ground, which happens to be the (+) side of the battery in this design. (An unfortunate choice of reference on my part... it made my life easier, but confused other people.)

But your IC2-pin1 does not sound right. With your black lead on IC2-pin2, measure the voltages on pins 3 & 1.

- Carl

[jhettel]

correct voltages

I have thoroughly checked all of my components and I do have the correct IC's installed, I could read the numbers and letters very distinctly, and they are installed in the proper areas. I do have the battery connector installed correctly, I was able to look at the schematic when I first installed the connector and determine which side the + lead went to. My positive (red lead) goes to the switched side. I was able to correctly connect the test leads from my multimeter and the voltage did read -12.20 at the battery and -12.20 at the center pin of IC3. The voltage at one of the outside pins did measure -4.95 and the other pin did read 0. So it appears that IC3 is connected properly and working fine. I did drop over to IC2, 78LO5 and that has nothing. So, again I am probably not connecting the leads properly. But, I am getting somewhere and feel that there is hope. Hopefully, when past this point I can make a little progress.

[Reg]

Ok,

Now, you should be able to measure the pins on IC4 and get the same readings as those on IC3. Verify this is true and remember to always place the - or black lead of your voltmeter on the ground pin. Also note that IC3 and IC4 are identical, so make sure to measure the same pin on IC4 as you did on IC3 and the voltages should match. It is positioned differently, so you will have to look just how it is mounted to determine which pin is which. Once you have verified IC4 is operating correctly, then you can go on to the next step.

Next, you can tackle IC2 which creates the +5V output. However, for this to work, you have to have IC1 and IC5 installed. IC1 is a switched capacitance voltage converter which converts the -12V to a +V. Also, the signal that causes the switching comes from IC 1, so, for IC2 to work, make sure IC I and IC5 and all associated circuitry for those two chips is connected. This means the FREQ and PULSE WIDTH pots and associated resistors, plus any cap that connects to IC 1 and IC2 is installed.

Now, IC2 is a 78L05 which has a different pin configuration than the 79L05 you previously measured. So, measuring it will be a little different than measuring IC3 and IC4. On IC2, One end pin connects to D2. This pin should measure a +V of maybe +8V to +10V or somewhere close. The middle pin is connected to ground on this IC so it should measure 0V. Finally, the other outer pin should measure a +5V or close to it.

Let me know how the +5V checks out.

Reg

[jhettel]

correct voltages

I checked IC4 and it checks out fine, identical to IC3. I will have to install the components for IC5 and do not want to rush myself and make a mistake so will probably not get that finished until Monday. Tomorrow (Sunday) I will be busy at a flag dedication and will not be home for most of the day. I will get back with you as soon as I get IC5, which I have placed in the socket, and its associated components installed. 'til then, thanks

[jhettel]

not exnough experience

I am still in the process of trying to find the right potentiometers for the mount on the box. I have printed out all of the relevent articles on the Hammerhead in the forums, so that may help me a bit on the assembly. Right now I do have many of the risistors installed for the next section so I can check the +5voltage, but still need to install the potentiometers and capacitors which I have finally been able to locate here in St. Louis. As I stated earlier I am taking this project real slow and making sure that everything is going right. My urge is to slap it together, but that will not work and I am not going to take the chance of messing up. Reading through Carl's recommendations I am going to mount the audio; mail pulse delay; transmit pulse width; autotune; and threshhold pots on the surface, and of course the on off switch. I have looked at many of the excellent photographs of other projects and all seem to differ a bit. One have very many knobs. I have made copies of all of the pictures of various hammerhead projects and boards and that will help a lot. Thanks for all of the help to Carl and Reg. I am getting some confidence that it will work finally!

[jhettel]

not exnough experience

I am finally back. It took a while for me to get the proper potentiometers and other items that I had forgotten to purchase. As stated previously, I had installed IC3 and IC4 and they checked out fine after I learned the proper way to connect the digital meter. As per your instructions I also installed IC1 and IC5. I also installed potentiometers R2; R3; R42; R45; and R46. Diode 6 & 7. Resistors R1; R4; R5; R37; R43; R42A; R47; R45A; R44; R48; R50; R46A. Capacitors C11; C26; C8; C9; C24; C25. I had previously installed all of the components for the power section. I have also installed of of the jumpers shown on the circuit board. I have not installed any transistors. As per your instructions I think that all of the above components support both IC5 and IC1, and you said to make sure all of the resistors and capacitors for those two IC's were installed. On checking IC2 I still do not have the +5 readings. I have checked it over and over again. All of the -5v and -12v readings are fine but I have "0" readings on all pins on IC2. If I could just get the proper readings on IC2 that would be an accomplishment. Glad for all of the help, but sorry for bugging you guys with all of the questions.

[Reg]

If you have a scope, you can look at TP 1 to see if you have pulses. If you only have a meter, then check the voltage at pin 3 on IC 5 (TP 1). You should see something other than 0 or -5V. If you switch to a/c voltage on the meter, I would think you would see some voltage there also. This will depend upon the meter, though. Most likely, if you have any voltage other than 0 or -5, the chip is oscillating. You could try to capacitively couple a high impedance speaker to TP 1 to see if there is a squeal. If you hear a squeal, and it varies in pitch when you adjust the pulse frequency pot, then the chip is working.

If it appears you have the oscillating voltage on TP 1, then look at pin 2 of IC 1 and see if something similar is happening. You should have some voltage other than 0V or -12V at this point.

Pin 2 of IC 1 has to be oscillating also to generate the +5V you need. If that signal is there, then carefully check the two diodes, D1 and D2 to make sure they are mounted properly. Also, make sure C 1 polarity is correct and is the right capacitance. It has to be 22 uf or greater to work correctly.

If IC 1 is pulsing correctly, the C 1 couples that pulse to the two diodes which will then rectify and convert the voltage to a positive voltage. So, you should see about a +10V at pin 3 of IC 2.

Now, if none of the signals appear to be there, you might pull C 11 and see if IC 1 works then. IC 1 can oscillate by itself if there is nothing wrong with the chip and it is installed correctly. Double check to see that it is a version of the 7660. This could be an ICL 7660, or have another prefix.

If you still have nothing, then double check to make sure there are no solder bridges on IC 1.

IC 1 should oscillate and this switching voltage is rectified by the two diodes, D1 and D2. The output at D2 should be a +Voltage of maybe about 10V or so.

Let us know how this checks out.

Reg