Deepstar problem

[gwarrow]

Hi All,

I have tried to contact Eric Foster via this site to no avail, maybe the experienced amongst you all could help with my technical problem... here goes.... When the machine is switched on and being used the threshold signal remains on all the time (as opposed to at least on my machine with a threshold that slightly fluctuates when machine is in motion) and even if you place the machine close to a metal spade for instance it has to be really close before it registers a signal. This occurs when the Deepstar is fully charged and only rights itself when the battery indicator has moved to half on the scale. I have noticed this symptom has progressively got worse ie on more than several outings........... after being used for a period of time the machine threshold reverts back to normal and then machine operates as expected ie. it goes very deep as Eric supplied me with a fifteen inch search coil.

Could this be the battery? I have eliminated the search coil because it works ok with my mates deepstar pack? which is the same model ie the mk 1 or first model out ......I have noticed that the signal of my mates machine seems very lively to mine (his machine has hardly been used where mine has had some hammer) any thoughts?

Thanks in advance for any advice!!

 

[Reg]

What happens when you turn the delay back a little when the detector is acting up. Does it suddenly begin to work fine?

 

[gwarrow]

hi thanks for your reply ... not sure I know what you mean by delay I normaly have threshold at 1 o clock sensitivity at quarterpast and reject off I sometimes back the threshold off for certain beaches cheers

 

[Reg]

The reject is more commonly called the delay control. Advance it when the detector isn't working correctly to see if the detector will work fine. Sometimes the coil changes a little and it will no longer work at the maximum delay, especially if it is a large coil.

So, if the detector has poor depth, then try advancing the reject control to see if the depth improves. Usually it doesn't take much of an adjustment.

Let me know if this makes sense.

Reg

 

[Reg]

Oops, I meant to say that if the delay is at minimum, the detector may not work correctly. Again, on earlier models, Eric called the delay control, the reject control.

Now, my guess is the problem is one of three things. First, maybe the coil has changed a little and won't work right at the minimum delay. The second possibility is the adjustment for the preamp or the preamp IC has changed a little and when the battery voltage is at maximum causes things to change just enough to cause your problem. More than likely it is the coil, though. The third item is if Eric used a regular on the supply to keep it constant, maybe that regulator isn't working right. If this is the case, then when the battery is fully charged, more voltage is going to the coil and this extra voltage is causing the coil decay signal to be just a little longer. A longer decay will or could cause the sample to happen too soon which causes the sample signal to be too great and it saturates the circuitry.

Regardless, this isn't a dramatic problem but one that is annoying that can be verified by advancing the reject control a little. If the detector works fine with the reject advanced a little when the battery is fully charged, then what is happening is one of the mentioned issues. My guess would be the coil changed a little.

Again, I suspect the coil is still fine but changed just a little causing the problem you mentioned.

Reg

 

[gwarrow]

thanks will try on next outing and report back!

 

[Reg]

One thing I didn't mention is just because a coil works fine on a different detector, it doesn't mean it will work on all detectors. Each detector has internal adjustments that are set to certain conditions and may not be adjusted the same. A small change can make a big change in how a coil works.

On most of Eric's models, he has an offset adjustment on the preamp and just a very slight change it that adjustment will cause or can cause a coil right on the edge of working to alter the signal enough that one of the later amplifiers goes into saturation. If this happens, the detector will sound muted or stated another way, may sound very weak.

Usually Eric has an internal reject or as it is called today, a delay adjustment that sets the minimal delay the detector has as its base. This adjustment is critical just as is the coil when trying to get the delay down to an honest 10 usec minimum. If this internal adjustment is set so that the minimum delay is just a little less it could cause your condition.

Now, as for checking whether the detector works well if the reject is advanced a little, a simple test can be done anywhere. I would expect your detector is very quiet even inside a house if tested with a full change. Now, if advancing the reject a little alters the problem, you should or could suddenly hear a much more obvious threshould with a lot more chatter and warble. My guess is it won't take but a very small adjustment for this to happen..

Reg

 

[gwarrow]

Hello Reg,

I 'm afraid due to circumstances I've only been out a few times since you last replied. I have checked and actioned all you suggested to no avail. However prior to going out with the deepstar last week end I looked at the jack plug and coil wire. I ended up swapping the jack plug from my beachscan and when rewirring it noticed the outer mesh of wire on the coil lead had perished(on the Deepstar).... I cut 2 inches off and re wired.

On site detector worked sporadically with similar symtoms as before.Sometimes working ok then a continuous tone with no metal detecting facility ie my spade normally shows a signal 3 -4 feet awy if im not careful but could move coil right over spade to get a signal... When back at home I noticed the conector on the coil was loose !

Any suggestions

Best Regards

Gwarrow

 

[Reg]

Hi Gwarrow,

Have you tried a different known working coil on your detector to see if it works ok? That is the best way to determine if the detector or the coil is the problem. You mentioned your friend tried your coil on his detector. Did you try his coil to see if it worked on your detector?

If your detector acts the same with any coil, I suspect the preamp stage is saturating. The adjustment requires a scope to get it right, but can be sort of checked with a voltmeter. The preamp stage either has a NE5534 or maybe a 709 chip if it is an old detector. Once the preamp is determined, then there should be a test point near pin 6, probably noted as TP1 or maybe TP2. Most likely, TP1. You can measure the DC voltage at this test point with the neg (black) lead on one of the ground connections and the red lead on the TP. You should read a very low voltage, probably less than 1 volt. If this voltage is near 4v it is at maximum indicating the preamp is out of adjustment.

If you can, take a couple close up pics of the pc board and send them to me.

Reg

 

[gwarrow]

Thanks Reg I will get back with a picture as soon as I can

Regards
Gwarrow

 

[gwarrow]

Reg, finally managed to get a photo of the inside of my deepstar

Best Regards

Gwarrow

 

[Reg]

Did you ever get the deepstar to work correctly? Did you get a chance to try other known good coils to see if it worked ok with any of them?

If the detector doesn't work right regardless of the coil used, look for an opamp a NE5534a or without the a on the board and see if there is a TP1 close to it. If so, measure the voltage at TP1 with the meter ground lead on a gnd point or the battery + lead and the red test lead on tp1. If you have a scope or know someone who owns one, check TP! with a scope. The signal should decay to 0V with no offset.

Let us know what you find out.

Reg

 

[gwarrow]

Hi Reg,

Im thinking of getting a deepstar 3 is it as good as my deepstar (mine is the 1st model) will my 15 inch coil work on the 3?

Im trying my deep star out next week back on the original coil

Best Regards

And thanks for your help

Gwarrow

 

[gwarrow]

Hi Reg,

My original coil works fine - 15 inch coil doesn't but works great on my mates Deepstar

Regards

Gwarrow

 

[Reg]

If your detector works fine with your original coil and your 15" coil works fine on your mates detector, then most likely everything is ok. It just means that your detector and your mate's detector are not calibrated the same or your mate's unit is newer.

Now, I mentioned this before, you need to turn on (advance) your reject control and advance it some to see if your detector works ok with the 15" coil. You may have to advance this control quite a bit before the detector works with your larger coil. On your detector, the delay control, the one that changes when the sample is taken is called the reject control. So, as the reject control is advanced, you are simply changing when the sample is taken. The later the sample is taken, the larger the coil will work on your detector.

On most of Eric's detectors, coils larger than 12" may not work at the minimum delay, which is the case when the reject control is at the off or minimum setting. By advancing this reject control, you sample later and that is what is needed to make larger coils work properly.

Eric installed an internal adjustment that sets the minimum setting of the reject control. So, all detectors may not be calibrated exactly alike. That is why you may have a larger coil work on one detector and not another detector,

Now, the Deepstar 3 is more advanced and probably has a shorter minimal delay. So, it probably will go a little deeper with the factory coil than your Deepstar 1.

Earlier I mentioned you should look for an IC with the numbers NE5534a but you may have a detector that uses a LM709 opamp instead of the NE5534a. On his later models, the 709 was replaced with the 5534a partly because the LM709 was no longer readily available. I don't know just when this changed occurred on the Deepstar series. So, you may have a LM709 instead of the NE5534a.

Reg

 

[gwarrow]

Reg, Many thanks for all your help! it's really appreciated!!

Gwarrow

 

[gwarrow]

Just to let you know Reg my new 2nd hand Deepstar 3 works great with the 15 ich coil and now looking forward to some serious detecting this year. My Deepstar 1 is working fine with the original coil too ....... Happy days!!!