CM15A RF reception range keeps changing

[pomonabill22]

I have had a cm15a for several years and did the antenna modification and got amazing range.
Then, a couple of months ago, we had some very close lightening strikes, and my range went south.
I have also had solar installed and the panels are on the roof close to the antenna for my cm15a.

So I though the lightening strike might have wiped out the receiver in the cm15a, and/or the solar panels were affecting the reception.
I spent several days moving the antenna in the attic, and didn't help at all.

Then I scoped the receiver's output, both the analog and the digital, and saw the digital signal wasn't very "clean".
The power supplies looked good at first glance, so I didn't suspect the receiver.
A note, I did change the receiver from the original.

Still no luck BUT here is what it was!!!

I looked again at the power supply and noticed the 5 volts had about 350mV of 35Khz noise on it, and that was affecting the AGC of the receiver!!!!

I changed the power supply caps (C2, C11, C12) because C12 esr was WIDE OPEN!!!, C11 was VERY high, and C2 was also very high, meaning they were not capacitors anymore.

I also added a 470uF directly on the IC's power pins, just for fun and added 0.1uF caps in alot of places.

RESULT was EXCELLENT range... seemingly better than ever too!  So the caps, being cheap low temp. caps, close to hot components like power resistor and voltage regulator, cooked and opened up.  Normal poor design.

So if your RF sensitivity seems to be failing, or has failed, you might want to look at the electrolytic caps.  Their value isn't critical, except their voltage (higher is better, IF they fit).

This is a similar problem with plug in modules failing.

[Brian H]

Thanks for the information.
Others have added four .1uF caps to the CM15A and improved things tremendously.
On IC's U1 & U3. Power Supply caps C11 and C12.

Found the schematic. Showing the added four capacitors.
http://web.archive.org/web/20150322033425/http://davehouston.org/CM15A.pdf

I have seen reports that X10WTI changed the PCB to accommodate easier to get surface mounted parts and I believe the RF circuits on the main PCB. So the caps maybe on different parts IDs now or even already there.

[solareclipse]

I need to improve my soldering and electronics skills.  Or just hope that Authinx releases a newer, better product.   

[dhouston]

I have seen reports that X10WTI changed the PCB to accommodate easier to get surface mounted parts and I believe the RF circuits on the main PCB. So the caps maybe on different parts IDs now or even already there.

I don't think they added the caps to the 2013 redesign.

[solareclipse]

Update: My CM15A had become so unreliable (and annoying) that I finally broke down and bought a used CM15A off eBay.  It works better than my old one ever did!  I can dim, it's receiving RF signals pretty reliably, still some problem rooms but those have always been the case.

Now I can experiment with repositioning the SR751 and PLC01 I bought to try and fix the problems and see if I can make an even stronger system.

[Brian H]

Thanks for the update.

[dave w]

I don't think they added the caps to the 2013 redesign.

I wonder if a SMD version would be more stable? (especially if the grounding around the chip was improved).