Big Boys Hobbies

Modified Harbor Freight Pinpointer w/ pics

Got a Thermistor you want to sell ?

Does anyone have 1 of the thermistors that is talked about on this thread,you might want to sell.

I only need the one,and not a whole pack.
Thanks
 
In the wiring diagram ,what resistor are we referring to ?
I have mine all apart and ready to reconnect with the new changes.
Thanks ...
 
I believe that I may have one.. I will have to check this afternoon..
 
OverKill said:
Big thank you to pan4au for sending the thermistor.
Now I just gotta find where its located on the board.
Click to expand...
YW, it's posted on the site.. I need to find it myself so I can replace one on my HF PP
 
I read the entire post the other day, sorry if this has been addressed and i forgot or missed it. I am not good with soldering and electronics. I ended up taking the information about the internal sensitivity setting and taking a screwdriver out with me to the field. When my HF pointer overheated, i turned DOWN the internal pot. 1/4 turn And it worked like a champ. No more over heating. I realise that this not rocket science what i did, but possibly someone in my shoes that does not want to solder anything can take something away from this. I have a good 1"-2" on iron targets still. Dependant on the metal for distance in my experiences so far.

Im a noob! First post! :woot:
 
Unloco said:
I read the entire post the other day, sorry if this has been addressed and i forgot or missed it. I am not good with soldering and electronics. I ended up taking the information about the internal sensitivity setting and taking a screwdriver out with me to the field. When my HF pointer overheated, i turned DOWN the internal pot. 1/4 turn And it worked like a champ. No more over heating. I realise that this not rocket science what i did, but possibly someone in my shoes that does not want to solder anything can take something away from this. I have a good 1"-2" on iron targets still. Dependant on the metal for distance in my experiences so far.

Im a noob! First post! :woot:
Click to expand...

I do same thing. in heat of summer it sounds off no matter what. I put outside knob midway and then adjust internal blue pot down until sound goes off. then should be good to go.
 
cen-tech

I don't know how many people read these posts but I wanted a cheap pinpointer and bought one of these. Now these are not true pinpointers but will function OK
I had a discount coupon and they had 3 in stock. I got home and played with it for a while and saw that it drifted when it warmed up like most of the others. I decided to try a new alkaline battery and found it would light up the led but would not chirp or sense metal. Took it back and tested the other 2 and found they would not work with the alkaline battery either. Hmmmm. I took that one back home to try to find out why. I did find that the old carbon zinc would work just fine. I did a little troubleshooting and found the voltage regulator would not regulate with the hotter battery. It put out only 1.3 volt--not enought to run the rest of electronics. With the old battery it regulated at 4.99volts and gave a chirp to indicate is was working. I have ordered some of the NTC resistors and when I get them in I will find out at that time if the voltage regulator faults because of higher voltage or of a slight over current. No it is not the switch. I jumpered the switch to make sure. I dont know how many of these are in the wild but someone else may have one like this and have some questions too, like why does it go off when turned upside down? I don't know yet. I know others do though.:?::?::?:
 
I have a couple of these that i have done mods on. I added a thermistor to mine(also replaced switch and added vibe motor and adjusted internal pot). It does fine above 45 or so degrees. With temps in the 30's it sounds off continually as soon as it gets switched on. I have noticed if i leave it on long enough it will eventually settle down and function reasonably well(still touchy if tipped anything except vertical). Maybe the components warm up or maybe the circuit running continuously drains the battery and drops the voltage. Either way if I shut it off for a few minutes and turn it back on it runs continuously again.

The thermistor seemed to stabilize the circuit far better in extreme warm temps than extreme cold. This is only my experience, and is anecdotal at best. I May try readjusting the internal pot at a lower ambient temp and see if that helps. Most never detect in frigid weather and will be completely satisfied with the thermistor add on. I intend to buy a couple more and mod them as gifts for some detectorists friends who don't care to do the project themselves.

Overall, I think they are a great value if you can do the mods. They will work ok without mods, but it's not as much fun(Ie:more adjusting, less time for targets) as when they are tuned up. If you are on a budget these are the way to go.
 
I just installed the NTC resistor and it did settle the constant fiddling with the sens knob down a lot. It seemed to make the internal pot more touchy to get the external sens pot centered. I wonder if the NTC resistor and r6 needs to be closer to 200 ohms each to get back to original specs. I've not done a lot of experimenting with NTCs before but it just seems to me that a wider range is needed to cover a range of temps. It is entirely usable as it is except for the hot battery problem I have. I do have until spring to dink around with it tho. I wonder what the original circuit came from and what all the values were? I'm sure the chinese borrowed this circuit from somewhere as it is somewhat more complicated than a BFO detector.:D Hey maybe 2 NTC's in series:?:
 
zorro55555 said:
I just installed the NTC resistor and it did settle the constant fiddling with the sens knob down a lot. It seemed to make the internal pot more touchy to get the external sens pot centered. I wonder if the NTC resistor and r6 needs to be closer to 200 ohms each to get back to original specs. I've not done a lot of experimenting with NTCs before but it just seems to me that a wider range is needed to cover a range of temps. It is entirely usable as it is except for the hot battery problem I have. I do have until spring to dink around with it tho. I wonder what the original circuit came from and what all the values were? I'm sure the chinese borrowed this circuit from somewhere as it is somewhat more complicated than a BFO detector.:D Hey maybe 2 NTC's in series:?:
Click to expand...

I have seen several other threads on various sites regarding improving these pin pointers. Some very knowledgeable people have added much to the conversations. The general consensus seems to be that the design limits the potential. I personally intend to continue using CenTech with the known mods. I also plan to get a Garrett ProPointer and see If it performs in a better variety of environments.
 
I just got mine and it seemed to be working erratically. I took it apart and it looks like there is a red glue or something like that on top of the POT/VR1 adjustable sensitivity screw thing. Is this normal? And why should the sensitivity knob be set to 50%/half way when adjusting the internal screw? Could it be I need to replace the switch as other posters have mentioned? Does the vibrating motor chew threw the battery faster? Got extra motors? Anyone got extra thermistors as well? Thanks.
- Aaron
 
TheIVJackal said:
Anyone? I'd like to know if I should return it or if it's normal, thanks.
Click to expand...

Even with the vibe motor, battery life is probably 15-20 hunts for me. you can order the parts on ebay pretty cheap. Order a few extra thermistors. I bought 5 thermistors for around 12 bucks so i could mod a few for friends.
 
TheIVJackal said:
Anyone? I'd like to know if I should return it or if it's normal, thanks.
Click to expand...
The red stuff on the adjustment pot is normal. It's put on there to hold the setting but is easily dislodged if you need to make an adjustment.

Putting the external knob to midway while setting the internal is done so that you have maximum leeway on either side to compensate for temperature or other factors as you adjust the threshold.

If it's really flaky, you may have bad switch wire connections. A few folks had reported that theirs came off the switch terminals. Easily soldered back on. But if the store is fairly close, go swap it out. Then do the mods.

I found it interesting that the circuit board is already made with the pads and traces to include a vibrating motor, and a switch to select tone or vibrate. There are also empty holes for an NTC device and I have a batch on the way. That is a Negative Temperature Compensating resistor and is very inexpensive. I wish they would have at least used that part, even if they had to up the price by a buck or two.

I had the same problem as others when I was out in the summer sun. When it gets too hot, you can't turn the outside knob down far enough to get it to threshold and you must cool the unit off in order for it to work again. The NTC greatly reduces or eliminates that heat problem.

Papa
 
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