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Need tips and help !
A friend brought me some "burned" Fisher 1265. Some extended batt.pack was
plugged with oposite polarities. MPSU51 died, also LM339 on the output.
I replaced them and for the "first look" everything works fine.......but..
1265 is acting normal as you switch it on for a minute or two,it
detects items good and act quite usual.After 2-3 minutes(sometimes less), the
sound starts to decay and finally pass out.No sound at all! At that exact
moment when trying to test batt. with pushing that button, the sound appears
loud and clear, like everyhing is normal.When releasing button, again no sound,
no detecting.After that, when switch device off and wait a minute, and than switch
it on again, everything acts normal again! No matter how many times i repeat that
procedure,always acts the same. Present voltage is +6.80V and -3.85V, with 12V batt.
I checked major number of components, finds nothing unusual.When unsolder lm336(zener)
the voltages leveled at +/- 6.7 V till 7V aprox.LM336 is o.k. on testing.When i put
another zener 2.5V or 2.7V instead LM336, again i have the same results like with
LM336. I soldered again almost all pads, just in case of "cold soldering".I left it
for 2-3 hours and when switch it on again , it works a much longer, almost 20-30 minutes
good.I gave it to a friend to test it(since he using that 1265 for over the 10 years and
he knows much better it's behavior). He was almost satisfied with it for the first hour or
two, but later he noticed that there is no way to adjust it so that device should work with
some minor background sound(he told me that is the best way to adjust 1265 on higher sensitivity
for prospecting coins).So no background sound,and no way to obtain it.He explain me that
on coin prospectin he is using both disc.-s, left one is adjusted on "2" and right one
on "4". "Sens" is highest. In that position you must hear a noticeable background tone,when
detect iron, 1265 is "clicking" over that tone, but when detecting a coin, 1265 is producing
loud and sharp tone. At the moment, device is not producing background tone and it is a bit
less sensitive, also my friend would like to return original behavior of the 1265.
Since I am not using 1265 or similar i am not very familliar with it. I checked and tried to
repair it but right now i do not have any idea more! Any body can help me ?
KT315,GEO,QUIAOZHI,CARL,MICHAEL,JPLAYER and others H E L P !!!
best regards
ivconic
One more thing!
Friend noticed too,that SENS button appear's like no effect at all when random switching on and
test it by turning it high or low.....!? Ts,ts,ts....
1265 is quite usable device on the field. I noticed many times, my friend is "dumping" pockets
with old Roman coins, detected with it.Also heard that 1266 has simillar results.Schematics are
almost the same. But when using bigger spider coil with 1266 it is a bit harder to pinpoint
exact position of a coin(which is o.k. by me, since it is larger coil).
So at the end, again, need urgent help about 1265.Any tip?
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