K2 backlighting brightness

[Ron ZL1TW]

Hi,
      I originally built my K2 #2204 about 5 years back, and have had a
ball with it, bringing it up to date with all the latest mods and small
alterations, but, like others on the reflector here, I was finally bitten
by the " build another kit" bug and consequently built myself another K2 #5577.
Both K2's go remarkably the same, but the older K2 has a noticeably dimmer
display than the new one which raises the questions :-
(1) Do the back light LED's dim with time?  ......the older K2 *has* had a
lot of use.
(2) Would changing R10 to (say) 22ohms have any detrimental effect  on the
life of the back light LCD's?
I'm not worried about current increase (I use a 40 amp supply) but would
such a change give me more back light without compromising components in
the Front panel board?(ie U3). I doubt there is a problem but it is always
wise to ask ..........
Cheers.......Ron ZL1TW
 


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[AA5CK]

Hi Ron

I went through this a few weeks ago. After trying several different
value resistors in parallel with R 10 I ended up with a 39 ohm one. This
dropped the the total resistance to about 18 ohms and increased the
current from the original 24 mA to 34 mA. Still not as bright as #5523
but close. Further increase in current didn't seem to increase the
brightness much so I went with the 39 ohm resister but YMMV.

I don't know about LEDs dimming but an increase in current may shorten
their life. Hopefully 5 mA per pair won't have a significant effect.
Maybe we'll get a more definitive answer from  the list.

This is really not a big problem and I am certain I would have never
noticed the difference in brightness had the two rigs not been setting
side by side and even then it took several days before I noticed it.

Good Luck....Ted...aa5ck


ron_w wrote:
>  
> Both K2's go remarkably the same, but the older K2 has a noticeably
> dimmer display than the new one which raises the questions :-
> (1) Do the back light LED's dim with time?  ......the older K2 *has*
> had a lot of use.
> (2) Would changing R10 to (say) 22ohms have any detrimental effect  on
> the life of the back light LCD's?
>  .
> Cheers.......Ron ZL1TW
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[Ron D'Eau Claire-2]

A few bits about LEDs, including a response to Ron, ZL1TW's question about
dimming over time.

LEDs do dim over time. Since they usually do not suffer catastrophic failure
that stops all output altogether (like an incandescent bulb does when the
filament fails) their end of life is typically measured as the point at
which the light output has dropped to 1/2 the original design value. That
operating life is generally in the vicinity of 100,000 hours.

LEDs can harm your eyesight! Peering directly into an LED can cause eye
damage. They are NOT lasers, but they can be very bright - much brighter
than an incandescent bulb of that size. The issue is that the light is being
emitted from a much smaller point source than other types of lamps,
including incandescent bulbs. You have nothing to fear from incidental light
from an LED, but some manufacturers warn against looking directly into an
LED at close range.

LEDs are current driven, not voltage driven. That is, the current through
the device determines the brightness and, unfortunately, the temperature of
the semiconductor inside. Higher than normal currents produce device heating
that will reduce the light output and decrease the operating life.

Like most epoxy-encased semiconductors, LEDs can EXPLODE when subjected to
serious over-currents. The bang is small, but the lamp sprays epoxy shrapnel
around. It could raise havoc with an eyeball that is close to it when it
happens. Actually, that's true of many types of transistors when subjected
to big over-currents, but LEDs seen to be the ones people are peering at
when they go off! There's nothing to worry about if they are being operated
at their proper current levels. The only danger is when the current-limiting
resistor is not correct for the voltage source.

LEDs can be damaged by ESD. Actually ANY semiconductor junction can be: it's
a matter of how big of an ESD charge reaches is. Most diodes are pretty hard
to hurt, so you won't find warnings to wear a wrist strap when handling them
in the Elecraft manuals. Still a jolt can do damage to an LED junction. It's
no where near as robust as, say, a power supply rectifier diode.

Ron AC7AC


-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of AA5CK
Sent: Wednesday, July 12, 2006 10:07 PM
To: ron_w
Cc: [hidden email]
Subject: Re: [Elecraft] K2 backlighting brightness


Hi Ron

I went through this a few weeks ago. After trying several different
value resistors in parallel with R 10 I ended up with a 39 ohm one. This
dropped the the total resistance to about 18 ohms and increased the
current from the original 24 mA to 34 mA. Still not as bright as #5523
but close. Further increase in current didn't seem to increase the
brightness much so I went with the 39 ohm resister but YMMV.

I don't know about LEDs dimming but an increase in current may shorten
their life. Hopefully 5 mA per pair won't have a significant effect.
Maybe we'll get a more definitive answer from  the list.

This is really not a big problem and I am certain I would have never
noticed the difference in brightness had the two rigs not been setting
side by side and even then it took several days before I noticed it.

Good Luck....Ted...aa5ck


ron_w wrote:
>  
> Both K2's go remarkably the same, but the older K2 has a noticeably
> dimmer display than the new one which raises the questions :-
> (1) Do the back light LED's dim with time?  ......the older K2 *has*
> had a lot of use.
> (2) Would changing R10 to (say) 22ohms have any detrimental effect  on
> the life of the back light LCD's?
>  .
> Cheers.......Ron ZL1TW
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[Mike S-8]

At 06:28 PM 7/12/2006, ron_w wrote...
>would such a change give me more back light without compromising components in the Front panel board?(ie U3). I doubt there is a problem but it is always wise to ask ..........

If you're equipped to desolder the display, you could replace the backlight LEDs with brighter ones. I used two Everlight EL-94-22UBGC arrays, which are available in the US from Mouser for a couple of buck each ( http://www.mouser.com/catalog/626/41.pdf ). They fit perfectly, I think the originals from Elecraft are the Everlight EL-94-22VGC. The relative brightness of these two different LED arrays is 133 vs. 35 mcd @ 20 ma, a very significant difference in brightness. They do change the display from green to a blue-green color.

I was then able to use a _larger_ R10 dropping resistor to get acceptable brightness (can't remember what I ended up with), so now I get the same current draw regardless of the day/night setting (with the night setting, the main display uses more power, but the meter LEDs use less).
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[Stephen Arnold]

Hello all,

This is my first post to the group so I hope it works correctly!

Happy to report that K2 S/N 5556 is alive in Australia!

However I'm slightly concerned about the results I'm getting during
transmitter alignment.

After running through the TX alignment procedure twice the best results I
can get for max power out are as follows:

80m - 8.1w
40m - 9.6w
30m - 10.8w
20m - 14.5w
17m - 13.6w
15m - 9.1w
12m - 10.5w
10m - 10.6w

These power figures come from the internal K2 power meter but a CB radio
pwr/swr meter connected between K2 and 50 ohm commercial dummy load agrees
with these figures with surprising accuracy.

The question being are these output figures 'normal'?

Output on 80m, 15m and perhaps even 40m seems a bit low to me. Simply
because I'm expecting to see 10w or more on each band.

In addition I got a 'Hi Cur' warning are soon as I raised the power level
to maximum. My K2 consistently draws 2.69A on all bands according to the
digital current meter in the power supply but the K2 current meter
registers values from 2.52A to 2.54A. I'm inclined to believe the K2 but
as yet have not checked the current draw with a meter. I have for the
moment increased the 'Hi Cur' warning threshold to 3.0A.

Again, same question, is this current draw 'normal' or abnormally high?

I have double checked the 80m bandpass filter components, toroid
type/number of turns and the capacitor values and all appears to be
correct.

So I'm not sure if I have a problem or not.

A sincere thanks guys for all your combined help getting me to this point.
No I haven't posted to the list before but when confused (and that
happened regularly !-) my questions were always answered by the list
archives!

Cheers from 'down-under'

Steve
VK2SJA

K2 S/N 5556

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[Stephen Arnold]

G'day again,

I feel such a fool!

I almost have to ask everyone to disregard my previous post.

After turning off all the equipment ready to shuffle off to bed (it's very
late/early here) I'm looking at the lab style bench power supply that I'm
using an realise that it's max supply current is only 2.5A. I was hitting
the current max of the supply and it was going into 'current limit'
dropping the supply voltage to about 10-11 volts and I had not realised.

Switching to a slighly larger lab supply capable of 3.0A output changes
things slightly! I'm now getting the following power output from my K2:-

80m - 17.2w
40m - 16.5w
30m - 15.7w
20m - 15.6w
17m - 15.6w
15m - 14.5w
12m - 14.0w
10m - 11.5w

Again these figures from the internal K2 power meter but the CB radio
pwr/swr meter agrees. Very happy chap with these figures :)

So now the only question that remains is the current draw. The K2 now
shows current draw values between 2.58A and 2.92A. Is this current draw
'normal' for these power output figures?

Cheers,

and sorry to trouble the group with my false alarm!

Steve
VK2SJA

K2 S/N 5556

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[Vin Cortina]

Steve,

Honestly, if we had a contest for the most unbelieveable, boneheaded,
mindless mistakes ever made in electronics, you wouldn't even come in the
running.  I would beat you and everyone else on this list so badly, they
would have to give "points" to even it up.

Just shake it off and go to the next step.

Regards,

Vin Cortina  KR2F

K1-4 s/n:1977
KX1  s/n:1476 (even still under construction)


-----Original Message-----
From: [hidden email]
[mailto:[hidden email]]On Behalf Of Stephen Arnold
Sent: Thursday, July 13, 2006 11:30 AM
To: [hidden email]
Subject: Re: [Elecraft] K2 S/N 5556 Transmitter Alignment - Doh!


G'day again,

I feel such a fool!

I almost have to ask everyone to disregard my previous post.

After turning off all the equipment ready to ...

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[Don Wilhelm-3]

Steve,

FB on your power supply confusion there.

The answer to your question depends on the voltage out of your power supply
(under load).  If it is only 12 volts, then my answer is yes, the current
draw is OK.  But if your power supply is developing 13.8 volts or a bit
more, then your current draw is a bit on the high side of normal.  It is not
so high that it would be something to worry about.  If you limit the power
to 12 watts, you will normally see 2.5 amps or less on all bands except for
10 meters.

Partial explaination: The K2 does internal power level control and will try
to ramp up the power to the level requested by the POWER knob.  To develop
12 watts with a 12 volt supply requires more current than if the voltage is
higher - it is a simple matter of Volts times Amps equals Power - the more
volts, the less current required since the K2 tries to keep the power
constant.

73,
Don W3FPR

> -----Original Message-----
>
> I almost have to ask everyone to disregard my previous post.
>
> After turning off all the equipment ready to shuffle off to bed (it's very
> late/early here) I'm looking at the lab style bench power supply that I'm
> using an realise that it's max supply current is only 2.5A. I was hitting
> the current max of the supply and it was going into 'current limit'
> dropping the supply voltage to about 10-11 volts and I had not realised.
>
> Switching to a slighly larger lab supply capable of 3.0A output changes
> things slightly! I'm now getting the following power output from my K2:-
>
> 80m - 17.2w
> 40m - 16.5w
> 30m - 15.7w
> 20m - 15.6w
> 17m - 15.6w
> 15m - 14.5w
> 12m - 14.0w
> 10m - 11.5w
>
> Again these figures from the internal K2 power meter but the CB radio
> pwr/swr meter agrees. Very happy chap with these figures :)
>
> So now the only question that remains is the current draw. The K2 now
> shows current draw values between 2.58A and 2.92A. Is this current draw
> 'normal' for these power output figures?
>
> Cheers,
>
> and sorry to trouble the group with my false alarm!
>
> Steve
> VK2SJA
>
> K2 S/N 5556
>

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[Stephen Arnold]

Hi Elecrafters,

Hoping that some of you may be able to point me in the right direction.
I'm not having much luck with power supplies!

Although a suitable level of audio volume is a somewhat personal and
subjective assessment I have spent some time now reading the list archives
re 'low audio' and I'm pretty certain that I have a problem.

My volume control needs to be set at 3:00pm or higher in the quite environ
of my shack with the RF gain at max to provide a listening level that for
me is just not quite loud enough. And no, I'm not hard of hearing.

Now I 'think' that I might know why I may have an audio problem. Which
brings us to the saga of the Power Supply Unit.

Having completed the K2 I moved it from the work-bench to the operating
table next to the computer. Ready to connect the K2 audio out to the
computer sound card for doing the filter alignments (Baudline and Linux).
In doing so I connected the K2 to a different 13.8vdc power supply from
the one that had been used during the build process. This power supply is
quite new, about 6 months old and sees daily service running my 2m rig.

I then plugged a 3.5m stereo extension lead into the front panel headphone
jack with the K2 happily running and then clambered under the desk to get
to the back of the computer tower. My trouble started when I went to plug
the other end of the stereo extension lead into the 'line-in' connector on
the sound card (can anyone see where this is going?).

There was a brief blue 'spark' upon plugging the audio lead in. That for
the split second in time that it takes for the mind to go "oh help that
was an arc!" and then "but that's impossible it's a audio line level cord"
followed by "oh s@&%! The K2 has powered itself off!" before I yanked the
cord back out. Seemed like an eternity but it probably all happened in
less than 2 seconds.

Power and audio were restored to the K2 as if nothing had happened. At
this point instead of getting scientific about my approach to fault
finding I went off in random directions and probably made things much
worse.

I triple checked the wiring of the speaker, external speaker connector and
plug. Having satisfied myself that all was perfectly correct I then
connected the stereo lead to the computer first and then plugged the other
end into the K2 external speaker connector. Please don't ask me why I did
this, just put it down to pure stupidity!!

This time I'm watching the K2. Sure enough big blue spark, K2 powers off
and I yank the audio lead back out again. K2 powered back up again. What
the??

At this point in the sad and sorry tale my immediate impression was "oh
help, I've blown the speaker". As the speaker audio level seemed to have
dropped by at least half and at that time I thought there was noticeably
more crackling on audio peaks. At least that was my "impression".

Only at this point did I put my brain into gear and start to do some
logical fault finding (too little, too late) and this is what I found:

The power supply in question has a correctly regulated 13.8vdc across its
output. But between the power supply case which is grounded to mains
supply earth and the negative terminal of the same supply there was a
voltage potential of nearly -25 volts (-24.7 something or other). This is
to say that the PSU negative terminal appears to be 25vdc below ground
potential.

When the K2 was interconnected with the computer via the audio lead there
would have been a 25vdc potential difference between the ground levels of
both machines.

Shorting the negative terminal of the PSU (now my least liked shack
accessory!) to its own case would cause the power supply output to fall to
zero (hence the K2 powering on and off). Holding that 'short' in place for
an extended period blew the mains fuse inside PSU.

So my questions are (and sorry this has been so long):

Can anyone think of a good reason as to why this behaviour from my PSU
would be normal or exceptable and why I shouldn't take it back to the
place of purchase and accidentally drop it on the foot of the first
salesman I find there (it's linear and quite heavy)?

Can anyone with a better understanding of the K2 circuit than I, predict
the result of placing +25vdc across the external speaker jack if only for
a micro-second or two?

Is this likely to be the cause of what I perceive as a low audio problem
or am I worried about a red-herring and my low audio problem, if I even
have one is likely to be unrelated?

Thanks again in advance!

Cheers,

Steve
VK2SJA

K2 S/N 5556

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