DX390/ATS818 Static Damage question...Again

DX390/ATS818 Static Damage question...Again

Post by Andy Domonko » Thu, 25 Feb 1999 04:00:00

I'm trying to repair a static damaged DX390 (ATS818) . FM/SW is fine but
MW is deaf. Dejanews came up empty as to which transistor is the likely
culprit. I remember reading a thread here years ago about one or two
FET's that were prone to static damage. I would appreciate any help.
Thanks!

Andy

UPDATE: Someone emailed me that the original posts about this date back
to 1994 and Dejanews doesn't go that far back.

 
 
 

DX390/ATS818 Static Damage question...Again

Post by or.. » Fri, 26 Feb 1999 04:00:00


It's the one closest to the ant. q1 q2? mine was a 2sk152 replaced it with a
mpf102 it works good,  am sw mw use this one if you have a long antenna you
my not notice it  on sw,  but that's the one, the mpf102 has the same pin
out but
the 2sk152 is more sensitive to weak signals MCM electronics has the 2sk152
for .50 if you want to use that one.

> I'm trying to repair a static damaged DX390 (ATS818) . FM/SW is fine but
> MW is deaf. Dejanews came up empty as to which transistor is the likely
> culprit. I remember reading a thread here years ago about one or two
> FET's that were prone to static damage. I would appreciate any help.
> Thanks!

> Andy

> UPDATE: Someone emailed me that the original posts about this date back
> to 1994 and Dejanews doesn't go that far back.

 
 
 

DX390/ATS818 Static Damage question...Again

Post by or.. » Fri, 26 Feb 1999 04:00:00

Here's the article your looking for

Fixing a dead DX390
This relates to the front end burn-out phenomenon associated with the Radio
Shack DX-390 multiband receiver. This happened to me with all the previously

documented symptoms and I was able to repair it by replacing the input FET
with
a device which is available off the shelf from Radio Shack.
After taking the DX-390's plastic enclosure apart by removing all the black
self tapping screws (don't forget the one down in the battery compartment)
and
lifting up the single p.c. board by unscrewing all the silver colored screws

which hold it down, you will find Q1 near the antenna connector which in my
radio was a 2SK152. Finding data on this Sony device is not easy and
replacement
devices are just as obscure. I get the impression that it is a low Ciss
small
signal N-JFET with moderate forward transconductance (>5mS)--a 2N4416 would
be
an excellent choice for replacement from an electrical standpoint. Not
having
one, I decided to buy a 2N3819 at Radio Shack (part number 276-2035, 99
cents
each). Actually, I bought two and used the one with the lowest rds(Vgs=0).
You
can measure this with a DVM by holding the gate and source together and
measuring the resistance from them to the drain. For a JFET, 1/rds ~= gfs. I

measured 275ohms, which would correspond to a gfs of 3.63mS, not great, but
not
bad.
Remove the dead Q1 by sucking the solder off of its p.c. pads with solder
wick
and measure it with the DVM to make sure it is dead mine looked like a 31
ohm
resistor from drain to source. A good FET would look like a pair of diodes
with
their anodes connected together at the gate. The gate is the lower terminal
looking at the device from the bottom with the flat side to your right; this

leads to an IMPORTANT difference in the DX-390's Q1 and the 2N3819 pin out:
the
source terminal is the same but the gate and drain must be interchanged.
This
means that when you replace the bad Q1 with a 2N3819, you must insulate the
2N3819 gate lead and twist it with the drain 180 degrees so the drain goes
into
the middle hole. For insulation, I used 1/8 inch of teflon insulation I
removed
from some #22 hookup wire. The transistor will stick up more than the
original
Q1 but this did not seem to cause any problems.
While you're at it, with the case open, you may want to disconnect the
annoying
buzzer by clipping its leads close to the p.c. board. Then, you can put the
whole receiver back together again. Mine seemed more sensitive than it was
before I repaired it, but this could have been my imagination.
Good luck and 73 DE AA1LL. The DX-390 is a handy receiver; I use mine mostly
for
portable c.w. and SSB utility and amateur monitoring. I also use it as a
second
station receiver to see what bands are active and/or full of QRM (this may
be
what blasted the receiver as on some frequencies I have transmitter r.f.
running
around the radio room which is on the second floor).
Paul Gili, AA1LL
5 White St.
Greenville, NH, 03048


> I'm trying to repair a static damaged DX390 (ATS818) . FM/SW is fine but
> MW is deaf. Dejanews came up empty as to which transistor is the likely
> culprit. I remember reading a thread here years ago about one or two
> FET's that were prone to static damage. I would appreciate any help.
> Thanks!

> Andy

> UPDATE: Someone emailed me that the original posts about this date back
> to 1994 and Dejanews doesn't go that far back.

 
 
 

DX390/ATS818 Static Damage question...Again

Post by Andy Domonko » Sat, 27 Feb 1999 04:00:00

Thank you very much for your help. I'll try the MPF 102 but may go ahead and
order the 2sk152 anyways.

Andy


> It's the one closest to the ant. q1 q2? mine was a 2sk152 replaced it with a
> mpf102 it works good,  am sw mw use this one if you have a long antenna you
> my not notice it  on sw,  but that's the one, the mpf102 has the same pin
> out but
> the 2sk152 is more sensitive to weak signals MCM electronics has the 2sk152
> for .50 if you want to use that one.