Q: Sangean ATS-803a static-sensitive transistor(s)

Q: Sangean ATS-803a static-sensitive transistor(s)

Post by Jim Hubba » Fri, 19 Aug 1994 15:25:00

Several months ago there were several posts which I neglected to save.

Sorry if this is redundant ...

The posts mentioned about some transistors in the Sangean ATS-803a that
are quite sensitive to static.  If I remember correctly, it/they were
connected fairly close to the whip antenna's input on the circuit-board.

I've tried reading the _tiny_ print of the included schematic, but it
about makes me cross-eyed!  Do you remember what the components were?

Thanks!

Regards,

Jim.

( Amateur radio:  KA3BPL )

 
 
 

Q: Sangean ATS-803a static-sensitive transistor(s)

Post by dsil.. » Sun, 21 Aug 1994 09:49:08



>The posts mentioned about some transistors in the Sangean ATS-803a that
>are quite sensitive to static.  If I remember correctly, it/they were
>connected fairly close to the whip antenna's input on the circuit-board.

You bet they are sensitive to static electricity entering from the antenna
circuit. One good static electric zap and the sensitivity of the unit went
down drastically. Sangean officially does not admit the problem, but it's
there. Especially in the winter. That's when there were several posts to
this board about the problem.

I don't remember if the exact component that failed was noted in any
of the posts, but it is in the FET. I'll check to see if I saved any of those
posts. If so, I'll send them to you.

Dave

 
 
 

Q: Sangean ATS-803a static-sensitive transistor(s)

Post by dsil.. » Tue, 23 Aug 1994 18:08:18

Well, Jim, you asked about the posts son this newsgroup regarding static
electricity with Sangean radios from last winter/spring. Here they are:
Regarding the problem with static electricity discharge
blowing Sangean (Radio Shack) shortwave radios. My own
experience is that I have a RS DX-370 (Sangean ATS-800A),
which I have had for several years without any problem with
static electricity. I also have a Sangean ATS-808 (RS DX-380)
which I purchased a year ago. As soon as the weather turned
cold, and the static electricity built up in my house, I blew
the sensitivity of the radio's AM (MW & SW) section by
plugging in an external antenna in the ATS-808 antenna jack.
The FM section seemed to be unaffected.

I returned the radio to Sangean, who replaced it under warranty.
Two days after receipt of the replacement, I blew that one by
hooking up an external antenna again. They sent me a second
replacement. I have been very careful with that unit, and have
had no problem since. I also have NEVER plugged in an external
antenna since I recieved the second replacement.

I have spoken with both the serviceman at Sangean and the
Sales Manager. The serviceman acknowledges the problem, and
has told management. Management including the sales manager
say there is no such problem.

Anyway, there were several posts to this newsgroup last winter
regarding this problem. I have saved them so here is a sample
of some of those postings. I do not agree or disagree with
what was been said. I am only reporting statements from some
of the newsgroup postings for you to read. The posts are not
necessarily in chronological order.

----------------------------------------
I have a RS DX-390 (Sangean ATS-818) which was destroyed by
static over the weekend when someone who shouldn't have been
touching it grabbed the antenna to adjust it without
discharging themselves of surplus static. I've read several
articles here about this problem, and wonder if anyone can
post the specifics again as to what part inside was actually
destroyed, where it is located on the board (ie: what obvious
capacitors, resistors, etc... is it close to), and where I can
get a new one to replace it.
-------------------------------------------
If DX-390 is similar to DX-400 (DX-400 is Sangean ATS-803),
then all you have to do is remove all the radio batteries,
including the backup ones for a couple of hours. This will
discharge the capacitors in the cpu and reset it. After a few
hours, replace the batteries or, better still, put in fresh
ones and see if the radio works.
-------------------------------------------
I understand that the problem is that the static electricity
zaps the FET in the unit. This has to be replaced. I don't
know how that is done, however. Sangean management insists
that the problem is only if someone uses an external antenna,
and that it will NOT happen through the whip antenna they
supply as part of the radio.

You have just confirmed what I and others have told Sangean. I
suggest that you write to Sangean in LS attn: Sales Mgr,
Sangean USA. This seems to be a major problem for some of us
in the parts of the US where static electricity is prevalent
in the cold weather.
-------------------------------------------
That would be wonderful, if it works. If what others are
saying - that the static electricity zaps the FET - then
nothing but replacement of the zapped component will do the job.
-------------------------------------------
I spent some time fiddling with my DX-440 (ATS-803A)..and
discovered something interesting.....I tried attaching an
external antenna and doing some other tests. I was switching
back and forth between the whip and connecting an external
longwire using the rear-panel phono jack and seeing what
effect the EXT/INT antenna switch had when I noticed two
things that might be of interest--they simulated the
no-sensitivity condition that the zapped radios displayed:

1) If that EXT/INT switch is not making good contact, it can
get wedged in a state where neither side is connected, it
seems. The radio then appears dead. Smartly flicking it from
one side to the other fixes this. I suspect some contact
cleaner inside the switch would also help.

2) At one point, after my repeatedly switching antenna inputs
and connecting a disconnecting the external longwire, the
radio seemed to go dead, with nothing but hiss coming out of
the audio, even when the display shoed it to be tuned to
frequencies that had had strong signals a few seconds before.
manipulating that antenna switch did nothing to cure this, but
turning the power off and on again fixed this immediately. I
found this to be particularly odd-- it seemed the
microprocessor needed resetting, but why would varying the RF
signal coming in cause it to go into an anomalous state?

Now, I haven't seen the rear panel of a DX-390 or its Sangean
equivalent (ATS808) so I don't know how similar this antenna
connection and switch is to the one on that model. But it
bears checking out. I really doubt that antenna switch is
designed for heavy use; its rear-panel location suggests the
designer expected it to be set once and then left alone. So
someone who repeatedly changes from internal to external
antennas may well wear it out, and a defective or damaged
switch could simulate a zapped front end.
-------------------------------------------
Is there any precise and specific test the user can do to
determine if their Sangean ATS-803A or Radio Shack DX-440 (or
other Sangean model or RS clone) has had this zapping? There
were such tests fro diagnosing the zapped FET front-end in the
Sony 2010, so it would help if the equivalent for the Sangean
line could be posted.

After reading all these posts, I am beginning to wonder about
my DX-440. It still has excellent medium-wave reception....
But maybe the thing is zapped? When the 2010 was zapped, the
medium-wave reception was the first thing to go.

When the Sangeans are zapped, will they still get reasonable
shortwave reception when using an external antenna, but not
with the whip? Or are they totally dead even with a longwire
connected to them? What happens to the MW reception on a
zapped Sangean? And is FM totally separate, so that FM
reception isn't affected at all?
-------------------------------------------
I posted an article a week ago about how I thought my DX-440
had been zapped. Thankfully, when I opened it up, all that had
happened was that the wire had become detached from the whip
antenna. Phew!
-------------------------------------------
It happened to me yesterday. I walked across a carpeted floor
while carrying my ATS-803A under my arm. When I reached the
other side and touched something, I got a static shock and the
Sangean is now definitely not working properly. The
sensitivity on FM is hopeless.

Can anyone please help with the FET type and precise location
on the Board??? I obviously need to replace the RF pre-amp
FET. Alternatively, does anyone know how I can contact Sangean?
-------------------------------------------
I had a problem with static electricity on my Emerson ATS-803
while on a camping trip. I had strung an external antenna up a
tree and static built up and screwed up the CPU inside.

I took it to a local Dealer, who said "I was lucky it wasn't
worse" as it turned out it was easy to fix. Just remove the
batteries until all capacitors discharged I haven't had any
problems since.
-------------------------------------------
All this talk of Sangeans getting Zapped has me kinda
concerned. I've got a 440 and a 380 and always use a reel
antenna inside and outside (strung thru trees). Am I gonna get
zapped, too?
-------------------------------------------
Your message mentioned zapping the front end of the Sangean
The front end of the Sangean 803A/DX440 has an FET which will
blow. It's Q115. Radio Shack used to sell the part which you
can use as a replacement, it's MPF102 and sells for 79 cents
(US). Hope this is useful.
-------------------------------------------
There have been numerous posts lon this newsnet regarding
zapping Sangean FETs with static electricity when using an
external antenna. Sangean admits this can happen.

Does anyone have any experiences to report of this happening
WITHOUT USE OF AN EXTERNAL ANTENNA?

Has anyone had their radio loose sensitivity when it has been
possible to have had a static electric charge go through the
radio?
-------------------------------------------
It happened to me, yes it did, I was sitting in my comfy chair
with my thinly veiled Sangean (RS DX-390) and the antenna
touched the lampstand which happened to be brass and well
grounded /******/ZAP/***********>,

Oh fabulous day, a warranty repair. (bought extended warranty
from RS""""""""Thinks: when DX390 is discontinued by the nice
Radio Shack people, there will still be a lot of static
electricity around.
-------------------------------------------
I have not had any problems with static electricity with my
2010 since I installed diodes in the antenna line, and kept my
old air-gap lightening arrestors in line (over the last 6
years or so at least). so the anecdotal evidence from you
perspective is pretty good!
-------------------------------------------
I'd imagine there is a large environmental effect to all this.
Years of reading the net has suggested to me that people in
the US have big problems with static in the colder months when
the air gets dry?
Here in Australia static is not such a big problem...this may
explain why my Sangean ATS-808 is and has been happy for quite
some time. It's a rare day in my part of the world you have
static trouble.
-------------------------------------------
When the FET blows shortwave reception goes completely dead,
even the strongest broadcasts i.e. BBC no longer can be heard
at full volume. AM sensitivity goes way down but strong
stations still come in. FM does not seem to be affected in any
way.

Watch out for static when connecting the antenna I have gotten
zapped ...

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