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RCI-2970N2 won't unkey

Discussion in 'General CB Services Discussion' started by cbkidd1, Mar 15, 2019.

  1. cbkidd1

    cbkidd1 Active Member

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    I wanted to hook up my 2970n2 to my Amp supply lk500 amp. In order to key the amp with the 2970n2 I was told to use the relay jack in the back of the amp. I ran a jumper from the relay jack to the inside of my D-104 and connected the ground from relay to the shield in mic and the positive side to transmit in mic. The amp did key up but when I went to unkey the mic the radio stayed keyed. I disconnected the mic from the radio hoping the radio would go back to receive mode but it stayed key up. I had the d-104 wired the same way to key my Henry 2KD5 amp with no issues. Would anyone know what damage I could have caused to the 2970n2? 73,


     

  2. cbkidd1

    cbkidd1 Active Member

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    Here is a picture I took of the cpu board. Not sure if this part is bad? But right in front of the two wire plug one is black the other white. There is a part not sure if it's a resistor but the top is white in color Could this need replaced?
     

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  3. nomadradio

    nomadradio Analog Retentive

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    First a little background about the mike jack on that radio. In a radio with no computer, the transmit pin on the mike socket is connected to a switching circuit that activates the transmitter and disables the receiver when you ground that pin with the mike switch.

    Your radio is different. The transmit pin on the mike socket is connected to an input pin on the CPU, the brain that runs the channel display and frequency control. That chip runs from 5 Volts DC. In receive mode, there is 5 Volts on the mike socket's transmit pin. You ground it to get transmit mode. The "TX" symbol appears on the display. Then, a separate output pin on the CPU activates the radio's transmit/receive switching circuit. The mike doesn't key the radio, the computer does. After you ask it to.

    Just one problem. You connected the 24-Volt relay circuit in the amplifier to the input pin of a 5-Volt chip.

    The chip won't blow instantly, but 24 Volts is still a quick death for the radio's 5-Volt CPU.

    And a permanent death. We have seen more than one attempt to connect a noise toy, external-keying relay or other 12-Volt device to the transmit pin of computerized radios like this one.

    The result is the same. The CPU chip develops a short to ground on that input pin.

    Inside the chip.

    Usual symptom is a radio that's stuck on transmit. It won't let you change frequency, and unplugging the mike won't make it receive.

    No way to reach inside the chip and clear the short.

    No way to obtain the surface-mount CPU chip as a separate part. Nobody has imported them, far as I know. Takes special tools and skills to remove and replace it without toasting the circuit board, anyway.

    Can't explain why it survived this treatment on the Henry amplifier. Should have blown out this chip before trying it on the LK500.

    Only fix is a whole new CPU/display board from RCI.

    Bummer.

    73
     
  4. OldTech03

    OldTech03 Sr. Member

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    Yeah, I remember those days I had anywhere from 2 to 3 every month come in from other shops that tried to do just what you said that was why I kept several of those boards in stock bummer but that's the end of that.......
     
  5. Dmans

    Dmans Well-Known Member

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    I used a similar set up 10 or so years ago (29995DX keying a Dentron......).

    In short I wired a separate small SPDT relay with a 12v coil to the frequency counter jack at the rear of the radio, supplied a negative to one side of the coil and found an 8-12v+ source when in transmit to close the relay and added a 1N914/1N4148 across the coil terminals. Ground lug of the Frequency counter RCA jack went to the common terminal of the relay and the center pin of the jack went to the normally open terminal of the relay. I think I "hot glued" the relay inside the radio and it worked fine for many years.

    The relay was similar to the link below.

    https://www.jameco.com/z/DS1E-M-DC1...ow-3A-12-Volt-360Ohm-Through-Hole_842734.html

    cbkidd1,
    The above may be good information to store for your next radio to amp set up. As Nomad and OldTech03 pointed out, your 2970 may be retired now.

    73's
    David
     
    Shadetree Mechanic likes this.
  6. cbkidd1

    cbkidd1 Active Member

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    As I sit here reading what Nomad is explaining. I realize how stupid that was of me to think that the microphone was going to key up the amp. So in the past, I had a general lee radio. And I also had this keying relay box that had come with the Henry 2KD5 I had bought and never used. So not being able to use the General Lee with the 2KD5. I had an idea and bought a KL-300P to use with the lee to be able to run the lee with the 2KD5. So in order to key the amp, I ran a 2 wire cable from the hot and ground inside the D-104 to the relay box and from there to the relay jack on the back of the Henry and it worked out great. Fast forward to yesterday. I had forgotten about the relay box and just ran the cable from the same D-104 straight into the relay plug on the lk500 amp. That's where all my trouble started with the radio. In one since it did work the amp keyed but at the cost of what Nomad said I fried the CPU board. Nomad has helped me so much Thu the years and at the same time taught me things as well. I don't know what I would have done if not for him and a few others on this site and CBT. That has taken time out of there lives to help me. And for that, I am very grateful. Being on a fixed income due to no fault of my own and not having the funds to put into this hobby. If something should go wrong like this. Without help from them, I am not sure if I would still be in this hobby So thank you all from the bottom of my heart. Think I got sidetracked lol. If I would replace the CPU board would that put the radio back in working order? 73,
     
  7. cbkidd1

    cbkidd1 Active Member

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    Dmans That sounds like what I need lol. I do have a few of those same relays. I left the relay box go with the Henry when I sold it. I should have kelp it. I wonder if that would work for the lk500 and 2970n2 if I can fix the radio. The only other radio I happen to have is an old original fm/am/ssb President Jackson that I bought used and the person forgot to mention that the finals were missing and the traces were they go are missing. I have the new finals just don't think I can fix the board.
     
    Dmans likes this.
  8. Dmans

    Dmans Well-Known Member

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    cbkidd1,
    Perhaps you could find a similar 2970n2 with burnt out finals and traces that has a good CPU?

    Good luck.

    73’s
    David
     
  9. cbkidd1

    cbkidd1 Active Member

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    Well loosecannon told me to try and remove cn605 plug in order to receive. So I unplugged it and it now receives great without it staying in transmit Mode. It won't let me change channels but at less I can receive and listen to ch 28. What really is bad I had been waiting to hear skip for the last few weeks that I have had the radio. Now that the radio is broken. Wouldn't you know it skip is rolling in? If not for bad luck I would not have any luck, Going to see if I can't find something to sale so I can buy a new CPU Board before I go nuts lol. Does anyone know if there is a CPU reset sequence I can try? Just don't want to overlook anything that mite help 73,
     
    #9 cbkidd1, Mar 16, 2019
    Last edited: Mar 16, 2019
  10. nomadradio

    nomadradio Analog Retentive

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    Would be nice if this were a "soft" failure that could be fixed by resetting the code stored in the CPU.

    Every time we see this, a check of the input pin on the CPU that connects to the mike socket shows a short to ground.

    Inside the CPU. That's a hard failure. Can't be fixed by re-flashing firmware. It's just broken. Permanently. Like a shorted protection diode, you need a new one.

    Bought my first Saturn Turbo 25 years ago cheap because it had this problem. The previous owner or tech had trouble with the relay inside the amplifier. Rather than just replace the bad relay, there were unshielded wires snaking out from under the amplifier's shield cover, across the inside of the radio and connected at the far end to an "ice-cube" size relay from RatShack. The coil on this relay was powered from the main 13.8 Volt supply, and was keyed with a wire that snaked over to pin 3 of the mike socket. This put the full 13.8-Volt supply voltage onto the input pin of the CPU.

    Showed the exact same symptom as your new radio. Ended up buying a 2950 mobile radio with a damaged main circuit board, but with a good CPU. Made one radio from the two.

    Over the years we have fixed this problem the same way, with mixed results. One customer wanted to fix his Galaxy DX2527 base after lightning hit his landline phone, which jumped to the D104 next to it on the desk. Same symptom. Stuck on transmit, could not change frequencies. He obtained a box with four salvaged CPU boards from the same 1995-version junked 2950 mobile radios. All of them were dead as a post. Leads me to wonder if the "horse-trader" who sold him the boards knew that none of them were any good. No way to tell.

    Finally found him a good CPU salvaged from a mobile. After trying a half-dozen that were bad.

    From 1992 or so to the present, this type radio has had between four and six different revisions of the CPU and display. For the most part they will not interchange. A used replacement must come from a radio of the same production type to be compatible.

    Led me to wonder what a person would pay for an aftermarket design. A drop-in replacement would take some programming effort. I'd favor a OLED display, rather than the LCD the factory uses. But I estimate the development cost to be several thousand bucks more than I have on hand to spend on such a project.

    There is an opportunity here for someone with deep pockets who can let the money ride while enough of them sell to break even.

    But that ain't me.

    Not this week.

    73
     
  11. TM86

    TM86 Ooohhh, shiny!

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    Anyone got a line to Mark19960? He did the board for the 980, he might consider this a challenge.

    Or not.
     
  12. nomadradio

    nomadradio Analog Retentive

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    Mark has the chops to do it, no doubt.

    But "can" is not the same as "will".

    73
     
  13. TM86

    TM86 Ooohhh, shiny!

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    Sure, drag reality into this.
     

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