Garrett Ace 250 coil not detecting metal

[Galan46]

Hi,
I have a 3-year-old Ace 250 that has been working without any issues but suddenly, it stopped picking up all types/sizes of metals. The original 9x6 coil is intact with no damage to the coil itself or the lead and to reassure me, I connected a friend's working 9x6 coil and it does not pick up either, so it's not the coil. All the keyboard functions display work ok as does the sound. The only thing I have noticed is that pressing and holding the pinpoint button and passing a large piece of metal (Stanley knife) close to the coil up to about 5", will make a positive sound (it will not pick up a coin or anything else that size even touching the coil). I have opened the control box and everything looks like new without any signs of damage or corrosion. Has anyone any suggestions of what can be wrong and is there anything else I can test/measure? Many thanks.

[kt315]

can you give a pic of back side of coil socket contacts pads?

[Carl-NC]

That's also where I would look. The connector is soldered directly to the PCB and stress may have cracked one of the solder connections. Probably a TX pin.

[Galan46]

I have re-soldered the 5 pins but still no pick-up. I have also found that the socket's threaded outer metal case (not the base or soldered inner pins) turns a fraction to either side with or without the coil's plug inserted. Switched on and manually twisting the socket makes some loud noise but no signs of detecting metal. I can easily replace this socket but the problem is, that I cannot find an exact match here in UK. All these aviation types of plugs and sockets available here come with a threaded body half the size of the one installed and there will be not enough thread to connect the plug. Pics attached (sorry I am having to take them indoors with artificial light as it's night-time here)

[kt315]

is there a cursor VDI as a reaction on a target and depth meter segments indicate right? or, no the sound and no LCD indication?

[pito]

check with oscilloscope for any signals on pins

[Carl-NC]

Sometimes the pins are "floating" so that they can move a bit for the mating connector, but I think that usually applies to the female connector, not the male connector. And moving the housing should not cause any response. This suggests there is something wrong with the connector. These connectors are made by dozens of factories with lots of variations. If it is the connector, you may have to go to Garrett to get a replacement since it could be difficult to find the exact match on the open market.

The next step I would suggest is to use an ohmmeter to see it any of the pins are intermittent or shorting to other pins when the housing is moved. As pito suggests, if you have an oscope you can see if the TX is working.

[Galan46]

Thank you all for your thoughts and recommendations. Unfortunately, my old oscilloscope is down and I am having trouble sourcing the spare bits I need. I have a friend that I could ask to check the pins for me but, be as it may, he is away for a couple of weeks so I'll have to wait until then. However, I have checked and rechecked the pins and the soldering and I do not think there is any problem there or indeed with the coil male connector. This connector outer threaded case bottom sits on a bare patch of the pcb, so no bad contact worry there and the five inner pins are isolated at the bottom by a plastic
base, so the slight rotation of the case does not move or affect the pins, both inner and the pcb soldered side, in any way. The noise I mentioned previously when touching the coil plug and the connector is not noted once the plug is fully inserted and tightened, as well as the coil cable wrapped round the stem.
Looking at the coil circuit diagram, I can see pins 1 and 5 are connected to earth. I have checked the resistance of the RX coil (pins 1-4 to be 0.56 ohms and the TX pins 2-3, 25.8 ohms) These readings are the same at the soldered pins end and, on the two coils I have connected to the board, so no problem there either. Checking the pins for intermitten or shorts does not show anything at all so I am stuck now. The option to send the detector to the Garrett's main dealer means, they will have a look at it and tell me it needs a new replacement board (as they do not have technical personnel to suss this out) at over £100 plus carriage expenses.

[kt315]

i see you have not soldering experience. it's bad. nickel layer on a metal is not soldering good. you have to tin the pins by active flux, before to solder the socket on pcb, i use zinc chloride.
remember you must wash off the pins by alcohol after that and then to solder it at pcb. do not use active flux directly on a pcb soldering never.

Zinc chloride is the name of inorganic chemical compounds with the formula ZnCl₂. It forms hydrates. Zinc chloride, anhydrous and its hydrates are colorless or white crystalline solids, and are highly soluble in water. Five hydrates of zinc chloride are known, as well as four forms of anhydrous zinc chloride.

[pito]

my old oscilloscope is down = google for sound card oscilloscope,




i am using this one https://www.sillanumsoft.org

RX coil (pins 1-4 to be 0.56 ohms and the TX pins 2-3, 25.8 ohms) = opposite way ?, low resistance = Tx, high resistance Rx.
Do you have anything on LCD ?

you can check Tx with headphones, connect them to Tx pin through 100nF capacitor, you should hear some sound.
check how much current is consuming your machine with the coil and without it, if there is a difference in tens of mA = Tx is working.

The noise I mentioned previously = Rx is working, put vacuum cleaner or battery drill close to your coil, turn it on = do you have any noise in the speaker ?

[pito]

[Galan46]

i see you have not soldering experience. it's bad. nickel layer on a metal is not soldering good. you have to tin the pins by active flux, before to solder the socket on pcb, i use zinc chloride.
remember you must wash off the pins by alcohol after that and then to solder it at pcb. do not use active flux directly on a pcb soldering never.

Zinc chloride is the name of inorganic chemical compounds with the formula ZnCl₂. It forms hydrates. Zinc chloride, anhydrous and its hydrates are colorless or white crystalline solids, and are highly soluble in water. Five hydrates of zinc chloride are known, as well as four forms of anhydrous zinc chloride.

I am an experienced troubleshooter going back to the good old "analogue" circuits of the 70's and I have never had any problems with my soldering. I did not have to un-soldered this connector, I only "touched the pins with my iron" to make sure there were no dry solder joints and should not have really bothered, as all the joints are the original without runs and all making good clean contact with their corresponding parts on the circuit board.

[Galan46]

Hi, Thanks for that. I was looking at my existing coil diagram which is slightly different, but yes, you are right, pins 1 and 4 are the Tx and 2 and 4 Rx. I just made a quoting mistake.
I have a full display of all the screen touch-pads and there is full sound from both speaker and headphones connector. Like I said at the beginning, if I hold the "pinpoint" button and wait for the sound to go down, waiving a large piece of metal over it, it seems to detect it with the correct loud sound. It will not react to a coin-size piece of metal and by large I mean just an all-metal Stanley Knife or similar.
I have looked at the feeding of the TX pin 4 to the OP37G chip by a 1k resistor and all is well there but I cannot, at the moment, follow it up any further until I get access to a scope.
I do not believe there is much wrong here because the detector has been working fine since new and suddenly stopped for no apparent reason. I am not the main user, it belongs to a good friend of mine.

[pito]

large piece of metal over it, it seems to detect it with the correct loud sound. It will not react to a coin-size piece of metal and by large = so connector connections are ok, probably Tx driver has a problem,
I have looked at the feeding of the TX pin 4 to the OP37G = OP37G it is a op amp so that it is a receiver.
To which IC is going another connector pin ?

[kt315]

sorry, not. this is NOT original circuit of the coil. onetime a coil was repaired by Ivan Kostin and he changed the connections
to his opinion seems more elegantly.