PI5 from ITMD

[surfdetector]

Been busy with other projects, so this one slipped through the cracks. It's on my list to revisit. If/when, I'll post the full details in the forum as a new project.
Don't hold your breath though .....it might take awhile.

I look forward to it.
Cheers

[Qiaozhi]

I am surprised that this topic did not ever take off and become an official project in its own right.

Been busy with other projects, so this one slipped through the cracks. It's on my list to revisit. If/when, I'll post the full details in the forum as a new project.
Don't hold your breath though .....it might take awhile.

[surfdetector]

pi5 is still a mystery machine

I am surprised that this topic did not ever take off and become an official project in its own right.

[bernte_one]

pi5 is still a mystery machine

[Qiaozhi]

After a cursory glance over the PCB layout, it is fairly obvious that the 5k pot is incorrectly connected. The layout has it connected between R15/C9 junction and +VB.

If you remove the 2N3904, 10R resistor, 5k pot and speaker; what does the audio signal at the junction of R15 (1k2) and C9 (100nF) look like on the scope? You should see a VCO style signal at this point which varies when a target is close to the coil.

Note that either the headphone circuit or the speaker circuit should be connected to hear the audio output, but not both together.

[geoscash1]

Thanks Ray, I'll run thru those test points today when I return from the doctors, thanks for your excellent advice.

[raygdunn]

Hi Ray,

Yep, I have a scope, just not enough electronics knowledge with this stuff to know where to start probing and what I'm actually looking for. I am using a rechargable 12v supply. I have tried using my bench supply with different settings and also 12.6v on three rechargbles. didnt seem to matter what the voltage was.

That would be cool to see what the chip pins give as far as voltage goes. I usually only check the voltages where the power pin is on each individual chip.

Bah. I've been here before I think. I do apologise. On the breadboard I have a PI-4 with the micro-processor back end. Plan B time...

Digging back though the thread, I found more details you have posted previously. At the time I was struggling with understanding the Barracuda. Can I suggest some tests for the scope based on that... I'm no expert 😞 Health warning applies☺

(Hopefully you are happy that a little over 12V is OK for the circuit, as was originally 9V. I've failed to confirm that so far.)

So one scope lead on the negative earth and with your PCB oriented with the word SPEAKER at the bottom.

(For anyone else reading this, references apply to the custom PCB not the schema. The designer software has allocated it's own numbering)

To check the timing pulse generator: (IC1 bottom left on your PCB). Pin 3 should show a square wave (of less than your supply voltage of 12V) if it is working.

Keeping clear of the coil area for now, if connected, as has that very high reverse voltage, which could kill the scope.

The next test point is the small voltage (less than a volt) across the diode pair D1, D2: test the end of either diode nearest the top of the board. If working there will be the squarish positive pulse followed be the brief negative, with that sloping trailing edge that we are all interested in.

Next point is the output of the preamp (5532 top right of centre): Output pin 1 should show the amplified previous signal.

The original positive pulse is filtered out by diode D3 (near top right edge).

We then go though those logic gates in the 4011 top right:
Pin 3 should show a now single pulse of near the supply voltage.
Pin 4 should show the same signal inverted.
Pins 10 and 11 will only show any pulses, if everything except the audio is functioning (including the second 555 checked below).

Looking at the sampling delay from the second 555 bottom right (IC2 on your PCB):
Pin 2 should have the input pulse starting the timer.
Pin 3 should have the output pulse after the delay time (controlled by pot. R18 on your PCB)

Then you are into the audio section.

I hope that makes sense and forms a useful initial test plan to isolate the problem.

Over to you...

Ray

[geoscash1]

Hi Ray,

Yep, I have a scope, just not enough electronics knowledge with this stuff to know where to start probing and what I'm actually looking for. I am using a rechargable 12v supply. I have tried using my bench supply with different settings and also 12.6v on three rechargbles. didnt seem to matter what the voltage was.

That would be cool to see what the chip pins give as far as voltage goes. I usually only check the voltages where the power pin is on each individual chip.

[raygdunn]

Thanks ray, thats kinda what I thought but wasnt sure based on the split connection from the pot to the 555.

I gave it a whirl and still get nothing though so there must be another issue elsewhere. I changed out the 555, 3904 and the 10R resistor as they were smoked but still not working.
Have power at all points so not sure what or where else to look with this thing.... Dang, was hoping that pot removed and new parts would be the fix...

In theory I still have most of the circuit on a breadboard. If you could give me your exact supply voltage, I'll try and give you some readings on the chip pins. I know they are not static voltages. But some ballpark figures should give clues. Let's hope I have enough to reconstruct a working for circuit again.

Do I take it that you don't have a scope?

Ray

[geoscash1]

Yes as in your diagrams, in my opinion.

I think you just remove the pot. from the PCB and you have the connections required in your revised diagram.

Ray

Thanks ray, thats kinda what I thought but wasnt sure based on the split connection from the pot to the 555.

I gave it a whirl and still get nothing though so there must be another issue elsewhere. I changed out the 555, 3904 and the 10R resistor as they were smoked but still not working.
Have power at all points so not sure what or where else to look with this thing.... Dang, was hoping that pot removed and new parts would be the fix...

[raygdunn]

Hi Ray,

based on your explanation then the correct connection should look like this:

[ATTACH]37309[/ATTACH]

versus how it was:

[ATTACH]37310[/ATTACH]

If that is right then how would I go about jumping or fixing the board I have made (based on the pcb shown above in other post)?

the 1.2k should go right to base of the 3904 but how would I get around the pre fabbed connections for the pot? Thats probably a dumb question but for whatever reason it is not clear in my head..

Yes as in your diagrams, in my opinion.

I think you just remove the pot. from the PCB and you have the connections required in your revised diagram.

Ray

[geoscash1]

Hi Ray,

based on your explanation then the correct connection should look like this:



versus how it was:



If that is right then how would I go about jumping or fixing the board I have made (based on the pcb shown above in other post)?

the 1.2k should go right to base of the 3904 but how would I get around the pre fabbed connections for the pot? Thats probably a dumb question but for whatever reason it is not clear in my head..

[raygdunn]

I circled where I think the issue lies, but am not totally sure. maybe the pinout of the 2N3904? or its connections. I have looked it over a thousand times but am not seeing the problem.

Any other eyes out there that can spot the issue. This circuit is burning up the 3904 and R17 the 10R resistor.

[ATTACH]37296[/ATTACH]

Hi,

I may have the answer, but I really am not that good at comparing PCB and differently numbered schema☺

The connections to your 555 seem to match my final schema (emailed by Q). However there is the bit on the right of my schema showing the headphones wiring and separated out the alternative with 3904 amplifying transistor to a speaker.

As I read the connections, there is still a 5K pot. that shouldn't be there, left over from the headset components. This is pulling the voltage going into the 3904 positive and switching it fully on. Hence your problem with the 10ohm resistor smoking (may have damaged speaker too). So remove the 5K pot. and hopefully...

It's the sort of problem you just wouldn't be looking for...

I hope that makes some sort of sense.

Ray

[geoscash1]

I circled where I think the issue lies, but am not totally sure. maybe the pinout of the 2N3904? or its connections. I have looked it over a thousand times but am not seeing the problem.

Any other eyes out there that can spot the issue. This circuit is burning up the 3904 and R17 the 10R resistor.

[geoscash1]

Hi geoscash1,

I don't think this is the bug you are looking for. The connections that you want for the 555 is Q's, the one on the right in his earlier posting above. Pins 6 and 7 look correct on your PCB image, without change, I think.

I breadboarded mine some time back, so wouldn't have encountered the problem.

So sorry to hear of your problem. I hope that I won't be following in your footsteps. I'm in in the queue (6 month waiting list!) for a colonoscopy at the moment. God what it is to get old...

Ray

Hey thanks Ray, I'll keep a prayer out for you as well. I think it is all the processed foods these days that is killing us all. time to get back to gardening real food.

Ok, back on the topic, I thought the problem was the connection from the 12k (r19 original/r11 my redraw) to pin 6 needing to be feeding pin 7 to be correct. But now that you mention it, I remember my issue was the 3904 and R17 (redraw) (10 ohm resistor) were burning up. so maybe the issue is with the wiring on the other 555. I'll have to regroup and look this all over agian to refresh my memory and get the schematic back in my mind to figure it out.

I had a friend redraw the circuit to pdf and make the pcb for me so I have the redrawn schematic and pcb image, I'll dig them out and maybe you guys can look them over with a fine tooth comb and see if you can spot any other mistakes I may have missed.

Thanks for the help on this, I reall think this design has potential and it has stuck with me since I first saw it so I really want to get it working.

Geo