Repair of Fisher 1260x

[wandering Mike]

Okay Dave, so what exactly is that potted front end module in the 1260x? You said it nulls out loop offsets, how? Mine module is stamped 202051. There are only nine PCB connections to it, so now my curiosity is fired up. Everything on the board looks good, none of the trimmers have been touched, all pots are clean inside, speaker is good, all solder joints are fresh and still clear-coated. But I'm wondering about the search coil, there are five pins not incl. gnd., is there a simple continuity test to determine whether it's working? Or does it need to be resistance tested, if so, what pin connections are used?
Thanks a lot for your help Dave 73 Mike

 

[Dave J.]

Mike, it's an oldie, I don't have schematic or pinout information for it. You might be able to find a schematic posted online someplace. Testing a searchcoil is more than continuity, you need to have a mostly working metal detector to measure loop offsets. And if the loop is bad it's probably non-repairable anyhow. .......Fixing a 1260 with unknown problems is a project I wouldn't want on my own workbench, so sorry, I can't be much help to you on it.

--Dave J.

 

[wandering Mike]

Hey, that's okay Dave, I understand, I'm a chronic tinkerer, I just get a little bored with ham radio and I needed a change, so I'l fiddle with it and see what I can come up with, I have an emal off to Fisher about the schematic, just have to wait and see on that. But here's a question I know you can answer; on the rear of the detector control box there's a coaxial "barrel" jack mounted off to one side of the coil connector, I'm used to seeing these things used for power connections on radios and such, but the only reason I can see for one on a metal detector would be for a battery charging circuit if you were using NiCds or NiMHs in the thing, but it looks like one lead of this jack goes to the headphone jack?!? I haven't touched a test lead to anything yet other than the battery holders, so it might just be a convenient chassis ground connection point. But you're the man Dave, what do you say it is? Again, many thanks. Mike

 

[Dave J.]

I'm guessing a recharging jack, you'll be able to figure it out from how it's wired. In the old Fisher machines the headphone jack was wired differently from most machines today, and the sleeve went to the negative rail ground which is also where one lead of a recharging jack would go. The other lead of a recharging jack would probably go to a rectifier, possibly wired in series with an incandescent bulb as a current limiter.

You picked the darndest thing to tinker with. If I were looking for something to tinker with, I'd try to build the world's best crystal radio. Better than the best one I built when I was a kid, and that one was VERY good, with high Q tuning circuit and the antenna and the headphone load impedance matched to the tuner so as to get maximum transfer of energy and not drag down the Q. Very few crystal sets pay attention to such details. In Sacramento I could occasionally pick up XERB in Tijuana, not only was it sensitive enough, but the tuning was sharp enough to get rid of the local KCRA and KFBK to be able to hear those more more distant nighttime stations.

--Dave J.

 

[wandering Mike]

Ha ha you're right, most people don't pay attention to circuit Q in crystal sets, but most people don't pay ANY attention to crystal sets nowadays. I'm currently restoring an old 1961 Heathkit GR-91 SW receiver, and just finished a 1965 Heathkit Mohican, so I thought the 1260x would be a nice change of pace. You might hear back from me saying I either got it working, or I cried "uncle", regardless, thanks for being an available platform for me to bounce a few things off of. Nice to have a pro around. 73 Michael