HH 38WXST channel mod

[junkmail1999]

Hello everyone. First post on this great forum. I hope one of you will be able to help me.
I have attempted the channel mod on this handheld Cobra but cannot access the upper and lower frequncies.
What I did was bridge J14, and fire up the radio and press "Freq" then "Scan" as the instructions I found
said to do but no luck.
Would anyone be able to shine a light on this for me.

Thanks all

[1 ADAM 12]

Frequnecy Mod

1. Remove battery compartment door.
2. Remove the 2 screws in the Battery compartment.
3. Remove the 2 screws at the belt clip
4. Measuring from outside bottom of radio up each side 3 1/8 inches (plus or
minus 1/8/ of an inch) at this point being very careful insert a very thin,
flat screwdriver and disengage the internal case connectors by pushing
straight in. I then bevel the cases mating edges to remove the marks made
disconnecting the case connectors.
5. Remove the top screw with brown fiber washer, located at the top center
of board.
6. Remove the PTT, Channel up and down, light side piece. You will see a
wire soldered to the shield covering, the CPU and to board ground, unsolder the
wire from the CPU shield below, and between the Channel up and Channel down
switches.
7. Now separate the front part from the Board. At the top Right of the CPU
Board is J14, two unused solder pads, bridge them. J14 is also just to the
right of R358 and to the left of the top right screw.
8. Reassemble Radio, turn on and press Function then scan and the U = upper
channels, the L = lower channels, and no U or L = CB Channels.

This is what I found on CB Tricks. Hope this helps.

[junkmail1999]

Hi, thanks for getting back to me.
Those are the instructions I used. The radio still works, but the upper and lower channels don't
show up.
The stuff I've read on the older handheld Cobras have you short a pin on the
cpu or a capacitor to reset the cpu. Maybe I will leave it unpowered without batteries
for a while to see if that works.

[MDYoungblood]

Hello junkmail1999,
Welcome to the forum. I've never done a cobra but have a couple Maxon's that converted well. If waiting for the battery/capacitor to die then firing it up again doesn't work try holding the function button while turning it on. Pushing the scan button once should put it in Low (L) twice in High (H) and three times back to CB.
As a new member could you post a intro in the "Welcome to the forum" topic, [Please login or register to view this link] ,so members can say "hello", thanks.

3's

Greg

[junkmail1999]

Thanks for the tip. I will give that a try. I haven't had a chance today to look at it.
I should do that right now.

-- Saturday, 24 January 2015, 16:18 PM --

Ok. An update. It works.
I tried letting the radio sit with no power or batteries connected to see if letting the caps drain would reset the cpu. Nope.
I then tried holding the function button while powering up the radio. No luck.
So I disassembled it again, checked that my bridge had continuity. It did.
So I saw there were 2 surface mounted caps that were accessible, so I shorted them to ground... and it worked. I believe they were C306 and C308.
I don't know for sure which one did it, but it worked.
I hope this helps someone trying to do this.

[MDYoungblood]

Glad you got it working. You could send a email to CB Tricks explaining what you did and maybe he would add that to the instructions. They are always updating their site.

3's

Greg

[KiethS]

I tried letting the radio sit with no power or batteries connected to see if letting the caps drain would reset the cpu. Nope.
...
So I saw there were 2 surface mounted caps that were accessible, so I shorted them to ground... and it worked. I believe they were C306 and C308.

As this radio model is still available at retail, though this thread is rather old, the info is still very helpful (I just bought one, for example).

I initially had the same experience after rework, with the radio tuner retaining it's original channel choices, and not enabling U/L choices.
Rather than re-open my reworked radio to temporarily short the caps listed, I simply unplugged the radio and kept it powered off for about 2 weeks, which had the same affect, draining the static memory, and enabling the Upper/Lower/Normal channel selection.

Glad you got it working. You could send a email to CB Tricks explaining what you did and maybe he would add that to the instructions. They are always updating their site.

3's

Greg

I wrote to the CB Tricks website webmaster, got a bounced back email from the provided address, and then I wrote to the registration admin contact to advise the need to edit their rework steps on the Cobra H38WXST to include a step to clear any static charge in the tuner's ram to enable the frequency toggle. I also provided the URL of the original rework instructions, and gave credit to this thread for the cap drain feedback.

Rather than to repeat my mistakes / delay, I advise that when performing the rework and with the radio still disassembled, for the tech to temporarily short the +/- sides of caps C306, C308 and of any other larger caps on the main controller board to ensure the controller / tuner's ram is cleared.

Most importantly, please ensure that any rework is performed in an ESD safe environment, wearing a grounding strap, etc.

[KiethS]

I am looking for a way to adjust one or more of the current Weather Channel frequencies on the Cobra 38WXST (for receive only, of course).
In my region, there are 2 available NOAA weather channels, and the rest of the presets receive only static (though they are used in other regions).

The NOAA weather channels are between 162.3625-162.5875 MHz, are FM wideband, and use up to 16 kHz bandwidth per channel.
I want to adjust one or more channels to receive Multi-Use Radio Service channels (151.820 MHz, 151.880 MHz, 151.940 MHz, 154.570 MHz), also FM, and they use either 11.25 kHz (those at 151.xx MHz) or 20 kHz (the 154.xx channel) bandwidth. Finding a way to adjust the fixed NOAA channels on this device could theoretically allow receiving select MURS frequencies and/or other fixed VHF-FM frequencies in the 2 Meter band, without having to carry a second device.

Reading the schematic, it appears the target circuits would in be the top-center section, "WX RF AMP. AND FIRST MIXER AREA". More specifically, near the 162-MHz L3/213CL, and 10-MHz L4/211CL area. I don't see individual settings for frequencies for each of the WX channels, so I'm guessing that's being addressed by the TK10930 IC. I'll need to pull a datasheet for that circuit to compare against the circuit. I'm concerned that changing the current circuit may allow tuning of only one channel, at the cost of losing all other (including 2 currently working) NOAA weather channels.

Has anyone else tried adjusting the fixed NOAA weather frequencies on this radio? If so, I would appreciate any feedback.

[MDYoungblood]

I believe your right, the IC does control the Weather portion of the radio, you can change frequency by adjusting the loads in that area but not sure what you will get, just remember where it was set at the start so you can get the weather freq's back. Not really much point in going for MURS band since it will only receive anyway.

3's

Greg

[KiethS]

Only "Normal" CB frequencies listed below are allowed in the US for use as the unlicensed CB band, but, if you've
modified your Cobra 38WXST handheld, it is technically no longer "type accepted" by the FCC for use as a CB radio.
Note that many of the L/U frequencies listed below are in use by various government organizations etc. ,
but none reach into the HAM bands from what I've seen. In any case, use only at your own risk (or don't).

As I didn't see this info posted elsewhere online, I created a table showing the frequencies resulting from this mod.
"L" is shown as "Lower", "U" is shown as "Upper", and no letter (CB channels) are is listed as "Normal".

Channel	Normal	Lower	Upper		Channel	Normal	Lower	Upper
1	26.965	26.515	27.415		21	27.215	26.765	27.665
2	26.975	26.525	27.425		22	27.225	26.775	27.675
3	26.985	26.535	27.435		23	27.255	26.805	27.705
4	27.005	26.555	27.455		24	27.235	26.785	27.685
5	27.015	26.565	27.465		25	27.245	26.795	27.695
6	27.025	26.575	27.475		26	27.265	26.815	27.715
7	27.035	26.585	27.485		27	27.275	26.865	27.725
8	27.055	26.605	27.505		28	27.285	26.835	27.735
9	27.065	26.615	27.515		29	27.295	26.845	27.745
10	27.075	26.625	27.525		30	27.305	26.855	27.755
11	27.085	26.635	27.535		31	27.315	26.865	27.765
12	27.105	26.655	27.555		32	27.325	26.875	27.775
13	27.115	26.665	27.565		33	27.335	26.885	27.785
14	27.125	26.675	27.575		34	27.345	26.895	27.795
15	27.135	26.685	27.585		35	27.355	26.905	27.805
16	27.155	26.705	27.605		36	27.365	26.915	27.815
17	27.165	26.715	27.615		37	27.375	26.925	27.825
18	27.175	26.725	27.625		38	27.385	26.935	27.835
19	27.185	26.735	27.635		39	27.395	26.945	27.845
20	27.205	26.755	27.655		40	27.405	26.955	27.855

p.s. Aside from the legality perspective, transmitting outside of the CB band will drive your VSWR out of tune, and
could damage your radio. Even within the CB band, the included rubber ducky antenna's tuning isn't ideal. I advise
to get an SWR meter, add an adjustable antenna, and "make that change" (save your radio, and improve your range!).

[nwc2bk]

Anyone have photos on the procedure?