Old Garrett BFO

[tonyja]

HI, I am trying to get in touch with "PAUL (CA)" ...He posted a pic of his Garrett BFO collection.. on Jan 14 2013., and I see my "Cache Hunter" (or something similar in his pictiure ) Here's my prob :

The 9V neg/pos battery connectors are going
It uses THREE 9 V batteries, and has a battery check switch with position '1' and '2' marked on the battery compartment door.
If the door is pulled off, the shelf holds two battery holders are apparent : '1' (on the right) and '2' (on the left). The other 2' battery holder is beneath the shelf..

I marked these, way back when, as I found the placement kinda counter-intuitive.. (you would think they would link the no, 2 test switch posiyion to the adjacent batteries on top of the shelf !! )

I worked out the polarity ,,,the batteries are in parallel, right ?

Anyway, not getting anything from the meter when I battery test,, but have 9 volts at all the wire connections attached to each battery. (There is nothing from the speaker, either.)

This detector WAS working ..well, years ago, ...it has never been brutalized, is in good shape, and has been in proper storage since.

Have some experience in circuits, and am wondering what the prob may be,, Fuse? Capacitor gone? Would love to hear what the "common", over-time problems are with these,,,
Live in Jamaica, and if anyone repairs them (still) I could try and ship it up..

I use a White's Surf PI as there's a ton of magnetic sand on the beaches here. The Garrett is a sentimental project

Thanks for any help
Tony in Jamaica

 

[Tom_in_CA]

If you start a thread asking for Paul (in the title) , he should chime in. Because I know he checks here from time-to-time.

And yes, he not only collects vintage machines, but is also not half-bad and tinkering with them. I've seen him do some awesome in-field repairs when he and I go out in the middle of nowhere, and his machine develops a wire problem, etc...

 

[Reg]

Hi Tony,

I suspect both batteries are disconnected by the on/off switch. Most likely, one of the two switches is not making up properly.

What I do is simply squirt the back of the switch with WD40 and work the switch a few times. Try to find a small opening where you can get the solvent into the back of the switch.

Try it, it can't hurt. I have done this on dozens of switchs with good results.

Reg

 

[Sweeping-4-junk]

When a manufacturer says they "don't have any more parts left" when you ask them if they can repair your machine the real reason is that they just can't be arsed to even try and fix it! Any old non working BFO should be an easy fix for any electronics engineer or repair tech.
Even a clever electronics student should be able to the get it oscillating and working again.with out too much of a problem The Search coils don't last forever on any machine , and chips can go low gain or faulty. I was in the electronics repair trade for 20 years and when I just could not be bothered to even try and fix a product you would tell the customer "sorry they don't make the parts for these any more" excuse excuse! Very true... This happens , 95% of detectors can be fixed , scrap detectors can be salvaged for a wealth of bits , so I can't see it been impossible to fix most machines up to 40 years old or so. How much effort the repairer wants to put into the job is the real key to success at electronic repair .

 

[n4ue]

Hi, even though I'm new to this group, I built my first metal detector (BFO) type for a high school science fair back in 1962.

The following is probably MORE than you ever needed to know about low voltage electrolytic caps!

One electronic component that degrades with age are electrolytic capacitors. They have a paste inside that dries out. New Old Stock caps are usually nfg, they may have been sitting on a shelf for years, drying out. Actually using a device that uses electrolytics, helps to keep them functioning by the activation of the paste and it's electrolytic function.

If a person wants to get into repair of any device that uses electrolytic caps, the best bet is an ESR meter. The VOM test is a crude but usable way to test them. Very small value caps will charge almost immediately, where as large value ones take a little time. You need an analog VOM for this, because the digital ones will be constantly changing.These ESR meters are available all over the www (and eBay). I use several in my shop and not only will they tell you the capacity of the cap, but also (MOST IMPORTANTLY) the ESR. Equivalent Series Resistance. A decent ESR meter will check the cap in-circuit since it uses a typical 100 KHz frequency at VERY low levels and won't damage other devices.
Most of the newer caps are made MUCH better than the old ones. If you have a choice, pick one with a 105 degree (C) rating, versus the normal 85 (C) rating. Cost difference is very small, the higher ones are just made a little better.

If you see a cap with a bulge on it's aluminum top. If time for a replacement as are any that show any sign of leaking. Most of the old radios and test equipment that come through my shop that are 20+ years old, gets new caps.

Just the ramblings of an old EE.....

ron
N4UE

 

[Tom_in_CA]

Hey ron, thanx for posting! Question for you: Was that machine you built capable of finding individual coins? Or was it only good for larger objects? If it could find individual coins, how deep could it find them too ? Like say ... dime. Or ... quarter, etc...