need tech help with these old units

[diver dan]

I've just inherited a pair of detectors that haven't been used in decades. (I've never used any metal detectors.)

One is a single 9V battery RB10. The other is a dual battery 840 Discriminator.

My first question is: Will the 840 work if one battery is brand new and the other is half used? I.e., how closely balanced does the supply have to be?

Putzing around with used batteries that I had laying around I observed the following:

The RB10 never made any noise from integral speaker or headphones. When I disconnect the cable to the search coil, it (needle) deflects to full scale. When I push the battery button it deflects to 25% of scale.

When I install only one battery in the "A" connector of the 840 and switch to "Battery, A" it deflects to 25% of scale. When I only install one battery in the "B" connector and switch to "Battery, B" I get the same thing.

When I install both batteries the thing immediately deflects to full scale and makes noise no matter if the the search coil is on the floor or high in the air. When I switch to "Battery, A" it tries to deflect to the left. When I switch to "Battery, B" it defects to more than 25% scale.

Does it sound like either of these need more than fresh batteries?

 

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[59CRL]

Hello. Yes try new batteries and see how they work. I have a few of the old classics myself, 2 of the 840's, a TR-550D and "Professional"
model from the mid 70's. Now the 840's and Red Barons sometimes break down, the 840's and they are repairable. Im rebuilding one
840 now which is half dead, battery function works but not the tuning.

 

[Phantasman]

I guess they may be better than nothing. Heavy, poor handle design (fatigue easily) and old "state of the art" circuitry.

If they work, fine. If you have to invest money to get them working, best to just get a used digital unit like a Quick Draw Pro. Some collector may see the value, but for everyday hunting, the QDP seems a better route.

Just my thoughts.