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White's Goldmaster GMT Rebuild

I've been a longtime fan of the White's Goldmaster series, but I was really annoyed when White's put the machine into the XLT packaging. I like to keep weight off my arm, but more importantly I work some very steep hills where putting a machine down can be a problem. The unit will simply roll to the bottom of the hill. I also work in muddy conditions a lot and so I do not want to set my detector down in the soup.

But I really wanted a new White's GMT. The automatic ground balance and LCD iron readout are very good. So I thought about what I might do to get what I wanted. A GMT to chest or hip mount. White's makes a chest mount version, but it has the darn handle/pod sticking out the front where it blocks vision and is prone to getting hit while digging. And for hip mounting it bumps into things.

White's GMT Chestmount
White's GMT Chest Mount Version

I went ahead and bought the chest mount version, but the following conversion can be applied to the standard model as well. I went with the chest mount as the rod assembly is already a separate item. 2011 Update: White's does not make their chest mount version any longer.

First step... take it apart! Here is the unit in parts, with a close up of the main board:

White's GMT components disassembled
White's GMT circuit board
White's GMT pod contents
White's GMT disassembled

The main board is clearly marked with what plugs where. Nice for reassembly. I took the pod apart, and ground the touchpad mounting down to just the pad itself as it was glued on too well to pry off. The LCD plugs into a mini circuit board in the pod, along with the trigger switch. Then a long cable runs through the handle and to a plug in the center of the main board.

I wanted to chest mount the unit with the coil cable and headphones running out the right side. This meant the LCD would have to be mounted on one side. That particular side does not have enough room to flush mount the LCD into the case, so I decided to cut a hole in that side and mount the LCD on the outside of the case. This meant the mini circuit board would have to be mounted inside the case lid where the speaker resides. I am a headphones guy anyway, so out came the speaker.

You could flush mount the LCD on the other side and retain the speaker, but then the coil cable will exit on the left. Good for lefties, however! You might even be able to do it the way I did and keep the speaker, but my fingers are not the most adept, and I figured I could use the extra work room.

White's GMT interior
Mounting the pod circuit board

The picture above shows the positioning of the mini circuit board inside the lid. The white ribbon cable runs out to the LCD. The green ribbon cable runs out through a hole I cut in the lid to the touchpad. I glued the touchpad on the outside of the case. More on that in a minute. The wires run to the new trigger switch location. I mounted the board on short spacer posts.

Modified White's GMT
Mounting the touchpad and LCD display

The picture above shows you where we are heading. The LCD is mounted outside the case. The LCD was mounted using the hardware that originally mounted it to the mini circuit board. A D-Ring has been repositioned to the left. The touchpad is glued down partially covering the speaker holes. The rectangular hole in the case was left after removing the handle. You can see the new trigger switch location. I'm going to replace this switch with one of the rubber capped types.

The touchpad covered the battery check/audio boost switch, so it was relocated to a position below the trigger switch. I had to lengthen the wires to do this, the only soldering involved. As I look down at the LCD, I can easily operate the switches and pad with my left hand. The switches are set so I can push down on them to activate the battery check or iron id accumulate mode.

modified GMT GRAB button
Relocated touchpad

I cut an aluminum faceplate to cover all the leftover holes and glued it in place. Painted it all black so it would look halfway ok. If I had it to do over again, I would make the faceplate at the same time as I was mounting the touchpad. It was hard to make the faceplate after the fact, and I had to dismount and remount the mini circuit board to drill the bolts mounting it through the faceplate. Better to glue down the faceplate and pad as a unit, THEN drill the holes for mounting the mini circuit board

Modified GMT iron meter
Relocated LCD display

This turned out to be the hardest part. I originally figured I would be able to find some kind of clear plastic box to glue over the LCD to protect it. I cruised aisles in Lowes, Kmart, and Fred Meyer for hours looking for any kind of little box I could cut down and use. Finally I decided to make one.

I got a piece of oak trim about 3/8" thick and made a bezel. I found a piece of thin plastic and made a window for it, and glued the window onto the bezel. I cut the original LCD stick-on window (the one that says "% probability of iron") down and glued it in place over my window. Finally, I glued the whole assembly over the LCD.

Imagine my surprise when I tested it out after the glue had set up and the LCD was missing half its pixels! I was bummed. I took the case apart and wiggled everything. The unit was working fine, just the LCD was acting funny. Finally I pried my carefully placed cover off and looked the LCD over. No obvious problems. It was still just barely readable, however, so I figured the heck with it, and glued the cover back on. After it set up, I tried it again, and now the LCD was almost totally blank!

I was using a glue called E6000 that bonds most anything. I decided that somehow the fumes from the glue had somehow "poisoned" the LCD. So I put a lamp on the unit and blew air in it periodically. And behold, the LCD slowly came back to life! Whew!! I cruised the net looking for info on this weird problem, but never did find anything.

Modified GMT chest mount  modified GMT hip mount
GMT conversion chest or hip mount

So here is the final product. Actually, as you can see, I took these before I did the trim work. The chest mount is just for show. I need to rig up a full harness. But I'll tell you what... I really liked it. Everything right there where I need it, but well out of harms way. The alternative hip mount setup is better than the original by far, but I liked the chest mount so much I will only use it like this where there is no trash to deal with. I'm still looking for that spot!

So there you go. This is not for the faint of heart. It was the first time I had done a mod this extensive, and it was a somewhat scary feeling to be tearing a brand new detector apart. Kiss that warranty goodbye! But now I have a unit I really like that will work well on steep slopes and other odd spots. Not to mention give my arm a break. The GMT is very well balanced, but every ounce counts when you are at it for 10 or 12 hours at a time.

A final note. You could leave the pod on the handle and route a longer cable from it up the coil cable and to the control box. But I wanted the pod off the handle entirely, and adding more cables seems like a way to ask for more problems down the road. I know another guy that has now done this mod after seeing mine, and a third is at work on his. Maybe some people going to all this effort will tell White's that their old box design was better.

Postscript: After the above post was made I took my new White's GMT chest mount to Ganes Creek, Alaska for a real world nugget hunt. The unit worked as I hoped and then some. Here is a picture of it and the 1.89 ounce gold nugget it found for me!

1.89 Ounce Nugget found at Ganes Creek, AK with White's GMT
1.89 Oz Nugget found with White's GMT Chestmount Conversion

Steve Herschbach
Originally posted March 24, 2002 Updated November 2011