Small got-ya to watch for when doing the K3 12VDC Out Current Mod

[WB4SON]

I set some time aside this weekend to install a second receiver in my K3,
and to perform the 12VDC Out Current Modification since I was adding a SVGA
card to my P3 (which requires more current than the stock 0.5 Amp output).
 My comments pertain to the latter.

Elecraft provides the modification kit with the SVGA card and it is very
easy in concept, requiring the removal of one SMT diode, and two thru-hole
components (a poly-fuse and a choke).  The bulk of the time involved is
strictly mechanical -- removing covers and sub assemblies to provide clean
access to the parts.

It was the mechanical aspect that immediately bit me in the backside.  My
K3 had been lovingly brought to life by the Elecraft factory this January.
 The first step to the modification is to remove the rear half of the
bottom cover.  Easy enough, remove 10 screws.  The instruction warns you
that three of the screws are part of a heat sink assembly which just
requires taking care to not lose the washers and other parts attaching the
LPA power transistors.  However three of the other screws attach to
standoffs that are fastened to the main PCB.  In my case, unscrewing two of
the black pan head screws on the bottom actually caused the hardware
attaching the standoffs to unscrew instead, dropping two screws and washer
inside the radio.  Full stop -- the last thing I wanted to do was flip the
radio over and lose those loose parts.  So I got eyes on the the loose
parts first (as I already had the top cover off for the Aux Receiver
install).

To avoid this, I would recommend taking the Top Cover off first, then using
a screwdriver to tighten down the two screws that are holding the standoffs
to the aluminum L-bracket that holds the PA.  Then I would remove the fan
assembly and PA assembly and tighten the third screw.  The LAST thing I
would do is remove the bottom cover -- while making sure that the L-bracket
screws don't come out (this is the FIRST step in the instruction).

My only other observations is use of a good solder sucker (one with high
vacuum) is probably helpful for removal of the two leaded components --
otherwise cutting the component body off and removing the leads while
heating them might be a good strategy if solder braid is the only available
option to remove the remaining solder.

The modification would have taken about 30 minutes had the standoffs not
come off at the wrong time, and the rework is easy if you have a decent
solder sucker.

73, Bob, WB4SON.
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[vk4tux]

I have the kit 12v output mod kit still sitting in the shack draw unfitted, and have been running the P3SVGA module > first in vk since they started shipping.

 I have had no issues and run the K3 at 15v.

[vk4tux]

Ok, I was thinking the P3/SVGA drew less current at 15v than 12v, due to the 5/3.3/2.5/2.2 v pwr supply setup requiring less current at 15v input than it does at 14v input or less.

I checked the K3 output with a 20 ohm/50w variable rheostat and it trips at 0.6amp or 600mA on my fluke 87.







What most people notice is that the P3 will switch off after a period of
operation when the resettable fuse finally heats enough to open. Your K3 may
have a defective resettable fuse in the 12V output line.

[Alan Bloom]

On Sun, 2012-09-09 at 20:50 -0700, vk4tux wrote:
> Ok, I was thinking the P3/SVGA drew less current at 15v than 12v, due to the
> 5/3.3/2.5/2.2 v pwr supply setup requiring less current at 15v input than it
> does at 14v input or less.

That's right.

> I checked the K3 output with a 20 ohm/50w variable rheostat and it trips at
> 0.6amp or 600mA on my fluke 87.

With a 15V supply, the P3 current is probably low enough that it will
run OK from the DC output jack of an unmodified K3.  The modification is
still worthwhile (1) so that the P3 will still work if you (or someone
else) tries to run it on a lower-voltage supply, and (2) because the
modification reduces the voltage drop to the DC output jack.

Alan N1AL

>
>
>
>
>
>
> What most people notice is that the P3 will switch off after a period of
> operation when the resettable fuse finally heats enough to open. Your K3 may
> have a defective resettable fuse in the 12V output line.
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/Small-got-ya-to-watch-for-when-doing-the-K3-12VDC-Out-Current-Mod-tp7562356p7562362.html
> Sent from the Elecraft mailing list archive at Nabble.com.
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[vk4tux]

Thankyou Alan, I guess for those like the OP and probably myself, that don’t like to get into the insides without a good reason;

Running the K3 at 15v (HD pwr cable too) works out great esp with all the other benefits, hence my observation to those hesitant to do the mod.

Adrian ... vk4tux

-----Original Message-----
From: Alan Bloom [mailto:[hidden email]]
Sent: Monday, 10 September 2012 3:58 PM
To: vk4tux
Cc: [hidden email]
Subject: Re: [Elecraft] Small got-ya to watch for when doing the K3 12VDC Out Current Mod

On Sun, 2012-09-09 at 20:50 -0700, vk4tux wrote:
> Ok, I was thinking the P3/SVGA drew less current at 15v than 12v, due
> to the
> 5/3.3/2.5/2.2 v pwr supply setup requiring less current at 15v input
> than it does at 14v input or less.

That's right.

> I checked the K3 output with a 20 ohm/50w variable rheostat and it
> trips at 0.6amp or 600mA on my fluke 87.

With a 15V supply, the P3 current is probably low enough that it will run OK from the DC output jack of an unmodified K3.  The modification is still worthwhile (1) so that the P3 will still work if you (or someone
else) tries to run it on a lower-voltage supply, and (2) because the modification reduces the voltage drop to the DC output jack.

Alan N1AL

>
>
>
>
>
>
> What most people notice is that the P3 will switch off after a period
> of operation when the resettable fuse finally heats enough to open.
> Your K3 may have a defective resettable fuse in the 12V output line.
>
>
>
> --
> View this message in context:
> http://elecraft.365791.n2.nabble.com/Small-got-ya-to-watch-for-when-do
> ing-the-K3-12VDC-Out-Current-Mod-tp7562356p7562362.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net Please help support this email
> list: http://www.qsl.net/donate.html
>

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