XL500 sample timing

[Qiaozhi]

My xl 500 is not working...well it was working fine I was at the beach with it and it was working very nicely..I went to use it the next day and Damn thing wont detect...there is sound like normal but the sound kind of drops out every few seconds and when I place a metal object past the coil I have no detection at all not even a whisper ...I havent been succesful to fix it ,I have no idea what it could be ...I have replaced all the capacitors and some transistors I have replaced the lm555 and because I have sockets I have tried the opamp and timer (lm555) but the faults are not there ,there are no shorted wires or bad connections anywhere and I have spent 3 days trying to find the fault...I need your help guys any Ideas where to look..

In order to successfully determine the cause of the problem , you need to systematically fault find, not just randomly replace parts in the hope of fixing it.

The very first thing you should always check is the battery, and then check the supply voltages are correct.

[Micheal]

Beutiful Austinmer beach

[Micheal]

My xl 500 is not working...well it was working fine I was at the beach with it and it was working very nicely..I went to use it the next day and Damn thing wont detect...there is sound like normal but the sound kind of drops out every few seconds and when I place a metal object past the coil I have no detection at all not even a whisper ...I havent been succesful to fix it ,I have no idea what it could be ...I have replaced all the capacitors and some transistors I have replaced the lm555 and because I have sockets I have tried the opamp and timer (lm555) but the faults are not there ,there are no shorted wires or bad connections anywhere and I have spent 3 days trying to find the fault...I need your help guys any Ideas where to look..

[homefire]

Dang! Cool case you have there.

What is it?

No I have not tried the 200 coil.

If I do I wold have to mess with damping resister and I really don't wish to mess around with it.

I need to get it sent to it's owner.

[Micheal]

Heres what I have done ...I have removed the vu meter because it was too big,I am waiting to get a lcd one that will fit nicely inside the clear cover.

[Micheal]

I had no luck with the hammerhead ....it blew a few things when I started it up first time ...I have actually started on something much easier the BRN PI-1.
I am about halfway through it it looks good and simple uses the PIC 16F876.I still need to get the pic and a few bits and pieces but Im not rushing this one.

But i still need to boost the xl 500 a little bit more(some help will be appreciated greatly).I have changed the housing so it is much smaller and lighter now ,yet still ok to use at the beach it,s one of those housings with the clear top.
I am wondering If homefire has tried the xl 200 coil on the xl 500 ...would you be kind enough homefire to try it out to see if it increases the sensitivity.Maybe that is all that I need for this machine and then I can just go out and buy one.

[porkluvr]

My mistake -
Woody does Minelab mods in Australia. I don't know if he does Garrett XL500 (not much help).

oops

Mr. Bill is who I meant to say. He does Whites Surfmaster mods. He is in in the states (sorry, Micheal).

Like I said, he does Surfmaster mods. I see certain similarities with that and the XL500 - uhmh well, they're both PI metal detectors. Maybe he can help with a XL.
Here is a thread on Surfmaster mods:
http://www.geotech1.com/forums/showthread.php?t=15070 is a thread on Surfmaster mods.

and Mr. Bill's website:
http://www.surfscanner.com/Surfscan3/To_Order.html

[homefire]

Who is this Woody? I have a Whites surf master circuit board and coil to play with.

[porkluvr]

Micheal. Your 709 has an offset voltage network connected to it that will not work with an NE5534. A proper change from 709 to NE5534 would require jumpers, cutting traces and voltage offset adjustment network component changes. And then you would need to scope it to tune it in. It is not a minor modification.

Don't do it. Look for Woody's website. He has a mod for the Whites Surfmaster I think. Maybe he knows your Garrett.

What happened with your Hammerhead?

[homefire]

The 2oo and 500 are the same boards. The 200 does not have the POT to set the Power levels. Not any more powerful, just quieter running with the shielding I think.

As the 2oo is not mine, I'm going to limit the MOD to the 5k and batteries.

I replaced the batteries that had pooped out with NiMh.

In stead of using the wood plug to take up the space of a battery, I just used the battery.
The machine does not see it as the regulators still are providing the same voltage.

The Guy I'm doing this for just informed me he has another 500 I can have after I send the 200 back.

That being so, I may try some of the MODs on the amps later.

I'm sure a better coil would bump things up on these.

[Micheal]

Homefire have you tried the XL200 sheilded coil on the XL500 if so did it make a difference.
And you know how when you turn the audio up until the tone is just hearable ,well this point is maximum sensitivity...Is it the same scenario with the XL 200?(I am just trying to figure out why the the xl200 is more powerful than the xl500 .

Regarding the 5k mod....today I removed the 4.7k resistor and put in a 4.3k and there was a slight but noticeable improvement so I thought then try a 3.9k resistor and the result with the 3.9 k was a reduction in sensitivity so I left the 4.3k resistor and found that this is the maximum that can be done with this mod.
The same washer which is very thin and very lightweight I would say weighing a quarter of a gram is now detectable at 10cm even 12cm but pulsey and faint ...My Australian 20cent coin is detectable at a maximum 40cm very faint at 42 cm with maximum sensitivity but faint and pulsey, and it is very clear at 35cm....test are done with the large 33cm coil...Also I have have removed the LM358 and put in place a LM1458 and the audio output at maximum sensitivity is a little more stable ....
I have made some coils for this thing but I now understand things a tiny bit better and will attempt a new coil around 25cm diameter and I will muck around with a diferrent damping resistor as soon as I work out which one it is...the coil is 1.2 ohms I am wondering if I increase this to 3.0ohms with more windings and a scotch 24 farraday sheilding .. should I get a bit more sensitivity out of it ....
The other thing I was wondering if the operating voltage is increased will I get more sensitivity like woody has done on his minelab sd 2000 ...would this mean changing the voltage regulators.
On page 1 of this post porkluvr has suggested to replace the 709 with NE5534 I will investigate this one...
and finally changing the 3300uf large blue capacitor to a larger say a 4700uf capacitor would this help.

[homefire]

The 200 was hotter then the 500 from the start.

Air test on my wife's home made gold (Gold I Panned ) ring was 5-7 inches with the 500. Modded 7-10 easy.

The 200 was at least a inch better from the start and improved by 4" Air test mod ed on the ring was a good

8-12 inches. In the field you would not hear it as good but PI perform better in the soil then in the Air so it may be a wash.

Both coils are the same looking from the outside.

The coil wire on the 200 is shielded and No External noise like the 500 can do.

Not Sure but I think the coil was shielded as well.

Later I plan on doing a spiral etched coil.

I think it would be hot on small gold nuggets. My original Intetions. Land Use.

Poor Mans Mine Lab?

I took these parameters from here on the forum but notice the coil for the 200 is not listed



XL500 7"149.5uH1.2-----
XL500 12.5"140.8uH0.746-
SeaHunter MkII 8"118.6uH1.18---
SeaHunter MkII 10x14107.2uH1.38------

Last number is ohms of coil.

Both seem to have the 7" version of coil.

I still say some more can be EEEked out of this machine.

[Micheal]

Homefire Have you done any air tests with the xl 200 with the small and large coil ...so I can compare it to mine and does the sheilded coil give better sensitivity...i hope you find a job soon( it can be pretty tough without a job)

[homefire]

Cool beans on your 500.

I've been unemployed for the past six months scrambling around looking for work.

5k was the best I could do on the mod, I think all machines have a few variables in the manufacturing process.

Any more Sensitivity is going to come from the Front End and Sample Amp I think.

When I have more time , I may play around.

I need to box up the 200 and send it off to the owner here soon.

The 200 is the better of the two machines.

They used shielded cable and I think the coil is shielded as well.

Intended for beach use, they had to address the ground effects better.

I will still have the 500 to play with.


Jim

[Micheal]

Hi guys ...after more fiddling with the XL500 I have been experimenting with the 5K mod which worked really well making a huge difference in sensitivity,I decided to go down to 4.7K resistor and I have got more sensitivity again ...at this stage it works nicely ,I have tried it on coins and a flat small and thin 5mm stainless steel washer weighing no more than quarter gram and it picked up at 7cm which is awsome for this machine.
I have tried 3K resistor which is too low and the machine loses total sensitivity...i will keep trying resistors between 4.7K down to 4k and try to find the optimum resistor here and will let you know what the results are.


My question is the XL 500 operates quietly at when the Audio knob(which is really the sensitivity knob) is turned up until the there is a tone.As the knob is turned for more sensitivity then at maximum sensitivity which is just before when the tone is just audible everything is sweet .But just after that point turn the knob anymore and then you are increasing this tone louder (similar to a gain or feedback affect)which overides the sensitivity ,so you have a loud tone with no sensitivity at high tone level....why does this happen.I have tried removing the LM358N so there is no tone and what is going to happen and the result was just the buzz from the current is audible to see if the problem is before the final stage and the affect is still there any ideas on squeazing more sensitivity out of this machine.There must be other things to look at besides the 4.7K that can be modded ...help wanted with this