Compass 77b

[Chiv]

I have acquired this detector non working at a good price so I think, Replace a few caps that where leaking on the board and then walla it works, happy days.
the only problem is the fine tune pot has sized and can not fine any numbers on it, the depth of the housing I was wondering if this was a multi turn pot. I have searched for a schematic and read quite a few post but not much available on this 77b. As I can not measure resistance on it been sized and if I try to take it out of the housing I Know it will tear of the shaft as it very corroded, looks like it either been in the water or high humidity
Can anyone put me in the right direction for this pot please

[waltr]

Which pot is your photo is seized and needs replacing?
The three silver colored ones are Not multi-turn. Just measure resistance across the outer two terminals after disconnecting the wires.

[Chiv]

It is the black one with the blue arrow pointing at it. I did not want to start pulling it apart just yet( while its working well) hopping some one could tell the style of this pot. the main or coarse adjustment is a 10k pot that I can read the number correctly as hard to read

[waltr]

Oh..I did not see that blue arrow.
Never saw a pot, with a coating like that before.

I would try a little (a few drops) WD-40 (penetrating oil) and let it soak for days.
This could get it un-seized.

[Tim]

It looks like the old ball-bearing type pots, which have no end stops-they just get slightly stiffer at each end of the adjustment but keep going around. Under the black cover should be a bearing race with several ball bearings in it. Perhaps electrical contact spray would work. If you need to spray it with WD or oil to free it up, be sure to rinse with contact spray then thoroughly dry before powering up.

[Qiaozhi]

This might help ->

[kt315]

Chiv
very (VERY) please read my opus before to do the pics

http://www.geotech1.com/forums/showt...here-share-out

[kt315]

please send the pics of your board and pots on my email [email protected]

[Chiv]

Thanks Tim, tried to pull cap of today and it popped the shaft a bit now have movement but lots of crunchy sounds and very notchy under the finger feel, it dose sort of work with dead spot in it so will replace it as soon as I get a chance.
Thank Qiaozhi, did find that on one of the older post.
NP kt315 have read you pic post, used a gpro for just a quick snap of pot but will get photo's of board for you when I have it apart again, I love the way it discriminates out iron and even black sand so very keen to get this detector working spot on, as have a lot of old miners camp site need going over (lots of iron scrap)

[Tim]

With enough rinsing the old tune pot should come good. According to KT's 77control.jpg it is 6K, so one of them blue multi-turn 5K's should work.
Gotta love the old Compass's. I have the 94B and the Judge 5. Missed out on a 77B pro on fleabay here in Oz the other week (darn!) due to lack of funds.
I traced out my 94B a while back and intend to Sprint up a board at some stage.
Your 77 should be ideal for the old camps. An old mate raked a camp at Tibooburra a few years ago with the neo-dymiums and got over an ounce out with his ML GP.

[homefire]

Tim. I have a 94B here . Seems to be working some. Need to go through it.

[Tim]

Tim. I have a 94B here . Seems to be working some. Need to go through it.

I remember when I got mine it wouldn't start oscillating. Worked out it needed warming up then switching off and on a couple of times. I changed the value of the inline R on the tuning pot, but it wasn't the problem. Connecting the R was kicking the oscillator into life. Now I just turn on for a couple of minutes, then off and on, and away she goes. I had it stored under the van bed,stacked up with others and when I pulled it out the coil wouldn't balance-must've got warped. After leaving standing with the coil flat on the ground (in the warm weather) it righted itself, thankfully.
I have found heaps of WW1 era coins with it around here amongst the rusty iron, and it will see my 1.7g of flour gold at 6 inches.

[homefire]

Yep. 100Khz can do that.

[Chiv]

please send the pics of your board and pots on my email [email protected]

Done sent with gmail googe drive to keep photo's in high mb so you can really blow them up, hope that's what you where chassing

[Chiv]

Gaday Tim you where right about it coming good, pulled the black cap of and gave it a good clean with contac cleaner, with shaft down hill so empty out of shaft collar, turn real sweet and as you sad it should load up at end of wined. very impressive 11 turn pot fine tunning at its best