Caused a short on my once working board, now it constantly beeps

[yatahaze323]

Hey Everyone,

I damaged something on my once working board. After putting the board in the box I built the sound was weak, so I took the board out and I was pushing in the IC's to make sure they weren't loose. While pushing in the IC's I was negligent and I had my metal ruler under the board while it had power going to it and I must have shorted out one of the components cause now my board constantly beeps.

The only thing I've done so far was to resolder everything just to make sure there were no loose connections but that didn't solve the problem. I'm not sure what component could have shorted out.

Whats the best way to go about find the damaged component?

Thank you everyone!

[kt315]

we just have in the arsenal of possibilites:
- op amp and comparator tester
- NE555's tester you can buy a kit on banggood for 2USD
- transistor tester that checks all. open CHINESE TOYS thread and find out about it

regards

[dbanner]

Hey Everyone,

I damaged something on my once working board. After putting the board in the box I built the sound was weak, so I took the board out and I was pushing in the IC's to make sure they weren't loose. While pushing in the IC's I was negligent and I had my metal ruler under the board while it had power going to it and I must have shorted out one of the components cause now my board constantly beeps.

The only thing I've done so far was to resolder everything just to make sure there were no loose connections but that didn't solve the problem. I'm not sure what component could have shorted out.

Whats the best way to go about find the damaged component?

Thank you everyone!

Check for correct power supply firstly remove all chips except 4024. Check -5v and +8v on the PCB. This is the first step.

[kt315]

you elementary forgot that this schematic without TX coil does not give -5V. you have to do small coil
6mH and check the board just with it.

[dbanner]

Yeah, I hope you had at least the TX coil connected, as tx oscillator provides clock pulse to 4024, whose output is used to get the -5V.
Tx colpits oscillator won't work unless the coil is connected.

[yatahaze323]

kt315, I do have one of those Chinese Toys so I can use that to test the components. I also have a multimeter if that could be useful.

dbanner, I had my board connected to the coil and the power supply is good.

I removed all of the IC's and the noise stops when I remove u107 LM358. I replace u107 with a new LM358 but that didn't stop the beeping. I guess I'm going to use the chinese toy to test all of the components in board first and see if I can find any damaged parts that way first.

Thanks for your help!

[dbanner]

Power supply good,ok.
Next step is to check diodes and transistors on board.(except the two transistors associated with the -5V supply which are good)
These can be checked without removing from PCB using multimeter. If all is well, Only connect the tx.
Next step is to check all chips in following manner. Install Rx preamp chip. Then next install last 393 comparator chip.(there should be two of them which you can swap). Still no constant beep? Then proceed with next 393 phase shift chip. Still no beep. Install remaining chips one at a time. The one who causes constant beep is culprit.
This is trial and error way of finding problem without having to be genius engineer.
Of course between each step you must turn off power supply.
I suspect the problem could be one of the 358 chips in either of the channels or a FET transistor.
As a matter of fact, you should check the status of the two FET switches first.

[yatahaze323]

Hi dbanner,

I followed your advice and I found one of the diodes was not working, I used the component tester(chinese toy) that kt315 mentioned and it said it was faulty. I replaced the diode and the constant beeping went away. I checked the rest of the diodes as well and the rest seem fine.

I now need to solve the other issue that I'm having.

The detector doesn't seem to be detecting correctly, in all metal mode its able to detect large metal objects but only about 2 inches and it can't even detect a usa quarter. I must have damaged something else as well. I've checked the coil connections and made sure that they were correct. I'll have to go through all the other components to see if I damaged anything else.

[dbanner]

If the detector is responding to metal with a beep, then all should be well with the circuit.
The problem is with the coil.
Was it working good before you shorted the diode?

[yatahaze323]

Yes the coil and board were working good before the diode issue. I plugged the coil into my other working TGSL and the coil functions fine.

[Hyena]

If you have solid tone, it means you probably have negative voltage problem. Do you have -6V on for example pin 4 on U101a?

Otherwise I propose to populate board and follow all testpoints from the document 101. This way you should localize you trouble spot very fast...

[yatahaze323]

Hey Hyena,

The board no longer has a solid tone, there was a damaged diode that I replaced. There are other problems with the board and I need to go through all the components to see what else is broken.

Thanks for the advice.