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Author Topic: Failed CM15A antenna mod attempt  (Read 602 times)

ronsonol

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Failed CM15A antenna mod attempt
« on: May 19, 2021, 10:12:39 PM »

I hope someone has ideas for me as I am at a loss for direction. 
I have a cm15A that for many years had not great range.  Trying to add some additional coverage I attempted the f connector mod. 

1. I snipped the existing wire leaving a length that I soldered to the center of the f connector and attached a small telescoping antenna. 
I grounded the f connector to the vss point.  Did not work, so then I grounded it to the ground point on the receiver.  Also didn't work. 
2. I removed the f connector and soldered a length of wire to existing length left from original antenna to make it 9 1/4", and it still didn't work.
3. Last thing I did was solder a new 9 1/4" wire directly to the board at the antenna point.   Didn't work.

Now to say it doesn't work isn't quite accurate, the cm15a occasionally picked up the signal but only if the palm remote is is basically right on top of the wire.  I went from around 10-15 feet range down to 1".

I've checked the rf board, no bridging of points at ground and antenna.  It gets 5v to the first pin.  The RF pin is showing around 2v, and will occasionally jump up to 3.4v or down to 1.4v when I press keys on the remote, but rarely does it work even with the remote nearly right on top of the unit.

I appreciate any guidance you have.
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Brian H

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Re: Failed CM15A antenna mod attempt
« Reply #1 on: May 20, 2021, 06:17:05 AM »

Is your CM15A the older designed model with a RF receiver and transmitter set of daughter boards soldered to it. Or one of the later models with the RF section all on the main board and has a surface mounted controller chip?

The older one is in the FCC Database and one of the files is the schematic of the original version and internal photos. That may give you some help.

https://apps.fcc.gov/oetcf/eas/reports/GenericSearch.cfm

Grantee B4S
Product Code CM15
In the details choice

Any possibility you have some sort of RF interference killing the reception?

There is also a good set of information here. https://www.laser.com/dhouston/ImproveCM15A.html
On the RF mod and ho we added 4 small capacitors to the main board for better operation. It is also the older designed model.
« Last Edit: May 20, 2021, 06:23:20 AM by Brian H »
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ronsonol

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Re: Failed CM15A antenna mod attempt
« Reply #2 on: May 20, 2021, 08:21:15 AM »

Hello, thanks for the reply.  I have the older model with independent RF boards.  I don't think it would be interference as it was working before I got my hands on it.

Thanks for the information I will check it out.
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ronsonol

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Re: Failed CM15A antenna mod attempt
« Reply #3 on: May 20, 2021, 08:41:32 AM »

I looked at the picture of the RF board and a couple things stand out to me.
In the picture by antenna is soldered to the point at the left red arrow.  And there does not seem to be the continuity to the components below as this picture would indicate being soldered directly to those components.  Also, the round solder point at the bottom with red arrow on right.  I don't have a solder blob there, but I did find a small piece that may have been knocked off.  Any idea is this is necessary, is it meant to bridge the round point just beside it?

RF board from database site mentioned above


Below is my RF Board.


The Blue marking indicates where I have continuity on the multi meter from the antenna wire.
It stops going any further beyond the blue marking.   The red lines indicated continuity between all those points. 

« Last Edit: May 20, 2021, 10:08:58 AM by ronsonol »
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bkenobi

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Re: Failed CM15A antenna mod attempt
« Reply #4 on: May 20, 2021, 10:26:42 AM »

I can't help with this, but I would like to point out that comparing the picture to your component won't help a whole lot.  It's pretty clear to me that your daughter board is different than the one from the FCC.  I would NOT attempt to make changes to the components to match the FCC picture when you don't have the same version.

FWIW, I always try to take pictures of things before I modify/fix them in case things don't work.  I then have a reference to what used to work or at least what it looked like before I touched it.  There are a lot of SMD resistors etc on that daughterboard and it would be fairly easy to melt solder on one which could allow it to slide to contact another solder blob.  Depending on what it's job was supposed to be, that could render things non-functional and/or permanently break things.

ronsonol

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Re: Failed CM15A antenna mod attempt
« Reply #5 on: May 20, 2021, 10:32:03 AM »

Thanks for the reply and yes I understand. 

Thing is though, my first 3 attempts to add a new antenna didn't even involve touching the RF board.  Only as a last resort did I solder a new wire to it, and I don't think there is any damage.  Just don't understand how the signal travels into the chip, if the continuity stops at the top cap.

Thanks again,
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bkenobi

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Re: Failed CM15A antenna mod attempt
« Reply #6 on: May 20, 2021, 10:50:51 AM »

RF is magic.  I'm an ME so the only thing I know for sure is when you let the magic smoke out, electronics dont work anymore.

Brian H

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Re: Failed CM15A antenna mod attempt
« Reply #7 on: May 20, 2021, 01:50:33 PM »

bkenobi Has found a difference in hardware versions.

The FCC database is the original version.

The one you have is a set of revised daughter boards with what looks like surface mounted parts. So do not use the database photos as a guide as it does not match your receiver board.

The solder blob was probably stuck on the board and not connecting things together. I would discard it and not try and find anything not properly connected.

The latest photos of the present version. Has the RF receiver and transmitter on the main board [screened PCB0051A in my photos] with surface mounted chips.

Is the receiver antenna wire the grey one in your versions receiver photo?

Was the receiving antenna wire inside the antenna tube or is it connected to a metal plate and the antenna is a separate assembly.

It is coupled with chip capacitors and maybe terminated by a resistor. With surface mounted parts. I would not suspect there would be continuity from the antenna to the receiver chip itself. As a functioning capacitor will read open with a meter and passes RF signals to the receiver chips antenna input and blocking DC voltages from the receivers input.

I will look at your photos and see if anything pops out.
« Last Edit: May 20, 2021, 03:23:55 PM by Brian H »
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dhouston

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Re: Failed CM15A antenna mod attempt
« Reply #8 on: May 20, 2021, 02:53:44 PM »

It is coupled with chip capacitors and maybe terminated by a resistor. With surface mounted parts. I would not suspect there would be continuity from the antenna to the receiver chip itself.
All the RF receivers I've seen couple the antenna through a capacitor.

The RX3310A datasheet shows schematics for typical applications.https://pdf1.alldatasheet.com/datasheet-pdf/view/1246343/PTC/RX3310A.html
« Last Edit: May 20, 2021, 03:24:42 PM by dhouston »
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ronsonol

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Re: Failed CM15A antenna mod attempt
« Reply #9 on: May 20, 2021, 04:52:12 PM »

Yes, the second/third picture is my rf board.
The grey wire in the picture is the current wire attached as the antenna.  I've tried a couple types of wire, and this grey wire I stole from the rf transmitter.
The Original wire was inside the antenna tube, but after the failed f connector mod attempt, it no longer is.

Thanks,
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Brian H

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Re: Failed CM15A antenna mod attempt
« Reply #10 on: May 20, 2021, 06:56:13 PM »

Look at the photos Blue Lines you used to indicate continuity. Make sure their isn't a solder blob or thin splash to the run around the top edge of the board.

Since you had the issue as soon as you moved the original antenna wire. I had wondered if moving it caused the antenna input on the receiver board and it touched something it was not meant to be connected.
« Last Edit: May 20, 2021, 06:59:22 PM by Brian H »
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ronsonol

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Re: Failed CM15A antenna mod attempt
« Reply #11 on: May 20, 2021, 07:06:32 PM »

I checked where the blue lines are, and there is no bridging of any sort to order areas.  The only connections are made with those points that are all linked to the same trace.
Thanks.
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dhouston

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Re: Failed CM15A antenna mod attempt
« Reply #12 on: May 20, 2021, 08:48:30 PM »

Just don't understand how the signal travels into the chip, if the continuity stops at the top cap.
Your meter will not show continuity through a capacitor as a capacitor does not pass DC but only AC.
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Brian H

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Re: Failed CM15A antenna mod attempt
« Reply #13 on: May 21, 2021, 06:19:37 AM »

I am not too sure if the receiver board with the 20 pin RX3310A chip shown in the FCC Database ever made it to production.

I have an early CM15A Date Code 04J41. It has a 18 pin RX3310A chip on it and looks very much like the photos you posted.
Mine has a silk screened H11245A 18 on the back side with a coil.
I just checked my latest CM15A Date Code 08B09. It also has a H11245A receiver board.

I will look at mine and see if anything pops out.

Since your first change was only connect the original antenna wire to the F connector. Maybe moving the wire caused the connection on the receiver to move and touch something or you somehow zapped the RX3310A chip and it is no longer functioning correctly.

If you are also doing things like timers and macros. On the power line. Are they still working and it is only the RF having a problem?
« Last Edit: May 21, 2021, 07:50:56 AM by Brian H »
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ronsonol

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Re: Failed CM15A antenna mod attempt
« Reply #14 on: May 21, 2021, 08:09:36 AM »

Hi, thanks again for the reply I really appreciate the help.  Everything else functions normally.  It is only RF reception that has issues.
I connected to Active Home, cleared memory and uploaded again with no improvements.  If I get the remote right up close to the antenna, almost touching, the RF reception does often work.  I can see that activity in the activity monitor and the corresponding device receive the signal over power line.
On the back of my board is =11245A 32, with the coil you mentioned.

I've done all the testing I can, resistors have the value in ohms they should.  Incoming 5.5v gets stepped down through two resistors. First to about 5.1v through 100ohm, and then to about 2 to 2.2v through 100k ohms before going to the chip. That cap the antenna travels through tests fine as far as I can tell, one leg to ground and the other not. Further down the path the other caps and inductor test fine before heading into pin 14.  The data output pin does make it to the chip P10792M on the mainboard at 2.2v.

Since I was careful with what I was doing before touching the board (remove from hot glue the length wound up inside and clipping old wire only)  I can't help but think something was special about the original wire or the fact it was in the plastic tube, but to me it just looked like simple aluminum stranded wire.

Also, on one of the data sheets I pulled up it says min input voltage is 2.4 volts, and max of 6v.  This might be the issue as I am only seeing between 2 to 2.2v. The 5v pin measure 5.5v, but after it travels through the resistors in series it drops to about 2.2.
« Last Edit: May 21, 2021, 08:55:19 AM by ronsonol »
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