Fisher 1220x coil values

[m23585]

Hi all. I have an old Fisher 1220x which works but not very good. I'm suspecting coil or cable problem as it gives different resistance and inductance values every time I measure. Any chance someone knows what those values should be? Thanks.

[kt315]

coil_data.txtI have not sure info Fisher 1220x adaptiving '1200 series coils' or something another and specific... Coils' Data Base is mainly grounded on Carl Moreland data...

[m23585]

After some browsing I was able to find that coils from 1225 and higher models (except 1260) will not work on 1220 model. From that file I can see that 1210 values are the same I'm getting sometimes on my 1220. So, thanks kt.

[kt315]

can you give pics inside 1220x, the board, for an archive? my email [email protected]

[kt315]

1260x coil specs
Fisher 1260x coil specs.pdf

[m23585]

Thanks again. Will do some pictures tomorrow.

[m23585]

Few pictures:

[muddy fingers]

I have a 1220X as above which coupled to a 3 and a half inch coil is now what converted to use as a discriminating probe. What is the large black component on the right of the first picture. I've never seen it anywhere else.

[m23585]

I wish to know that as well. I though it's just a piece of plastic protecting whatever is inside. But it can not be removed. So, you mean you don't have this in yours?

[kt315]

thank you much m23785 for the nice hi res pics. large black block is some kinda a protection from coping, IMO. it has a part of schematic. I see the similar block in 1212x schematic.

[muddy fingers]

Yes, my 1220 has this huge component inside, roughly 2" width X 1 and a half inches high. Looks as though it is an IC judging by the schematic. Is it an op amp which is now obselete. Originally made by Texas Instruments part 3606 BG. I meant that I've never seen it in any other detector or anywhere. My 1220 had a piece of wood inside of it as well, I remember. I was the first one in my club to get one of these new "motion" machines and I cleaned out the site of hammered coins the first time I used it. By the second week though, loads of members had bought similar, so my advantage was short lived.

[Dave J.]

The "huge component" is the front end board, which contained what we regarded at that time as trade secrets so we potted it in epoxy to keep it from prying eyes. It was eventually dissected anyhow and the schematic published, probably here.

As I recall the inductance of both the transmitter and the receiver circuits was 6.3 mH and the resonating capacitance for both was 0.22 uF. As I recall the caps were in the searchcoil but I may be mistaken about that. The caps have to be matched to within 1%.

The 1260, 1220, 1210, and as I recall the 1212 all used the same searchcoil, difference being that the cheepies were hardwired, no searchcoil cable connector.

[Funfinder]

Hey cool Dave J. that you worked personally on the Fisher, I still have my 1266x.



> I have an old Fisher 1220x which works but not very good.

Think it helps if you replace the old electrolyte condensers with fresh ones.
Especially those with the yellowish shine nearby the large transistor or what it is looks bad.
Thx for the pix.