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Arcom RC210 Not Responding to COS Input on Any Port (Confirmed Good Repeaters)

 

Hi all, Re-posting this as for some reason our first post never made it through:?

We're running into a major issue with a recently assembled RC210 — it’s not responding to valid COS signals or PTT (besides manually triggering it) on any of the three ports, even though the connected repeaters are confirmed working.

We're interfacing with both a Motorola XPR8300 and a Kenwood TKR-740 — and here’s what we’ve confirmed:

Repeater Tests (XPR8300 & TKR-740)

  • COS (Pin 21 / GPIO3 on XPR8300): Drops from ~4.66V to ~0.53V when receiving a signal (confirmed using XPR Pin 16 as GND).
  • PTT (Pin 17 / GPIO1): Keys repeater successfully when pulled low.
  • We repeated these tests using a Kenwood TKR-740 repeater with the same result — valid COS signals present and working as expected.
  • All measurements taken directly at the repeater accessory connectors using a multimeter. RC210 was disconnected for isolation testing.

RC210 Fails to Detect COS

  • All jumpers set per manual (e.g., JP2 = 1–2 for Active Low input on Port 1).
  • GND is confirmed clean and consistent across DB9 pins 6, 8, and 9.
  • Simulating COS by shorting DB9 Pin 7 (COS IN) to Pin 6 (GND) results in:
    • No COS LED
    • No PTT trigger
    • No voltage drop on PTT OUT (Pin 3)
  • However, manually shorting DB9 Pin 3 to GND causes the PTT LED to light and voltage to drop to 0V — confirming the RC210's PTT output circuitry is working correctly. ** All three ports, no automatic PTT detection either **
  • Same behavior confirmed on Ports 1, 2, and 3 — no COS detection on any port.

We had this unit assembled by Mr. Ken at Arcom, and he sent it back to us in a timely manner, we also emailed him our findings as well, hopefully he can help us with this.

?

Additionally, during troubleshooting the board, we found several clipped component leads left between pads and vias. We removed these and looked over the board for any shorted traces etc. - the bigger concern remains the complete failure of COS input logic.

  • Looking for any guidance from other users in the group in the meantime.
  • Perhaps any other others of the XPR8300/8400 would also share their experiences and their pinning, we included a snapshot of our CPS Accy settings.

Has anyone else seen this issue before? Could all three COS input stages actually be defective, or are we missing a board-level config step? … We did successfully connect it to the PC software but did not change any default settings, as it should have worked at least on the ‘basic default’ settings without changing anything correct?

?

Thanks in advance,
Bryan, KB9UZO

Eastern Colorado Repeater Association-ECRA

4-4-25 config.JPG
xpr 8300 acc pinouts.JPG
XPR_Mobile_pinout.png
IMG_0328.jpeg
IMG_0327.jpeg
IMG_0325.jpeg
IMG_0326.jpeg

 

Responded to privately



At 07:02 AM 4/6/2025, you wrote:

Hi all, Re-posting this as for some reason our first post never made it through:?

We're running into a major issue with a recently assembled RC210 — it?�?s not responding to valid COS signaals or PTT (besides manually triggering it) on any of the three ports, even though the connected repeaters are confirmed working.

We're interfacing with both a Motorola XPR8300 and a Kenwood TKR-740 — and here?�?s what we?�?ve conffirmed:
Repeater Tests (XPR8300 & TKR-740)
  • COS (Pin 21 / GPIO3 on XPR8300): Drops from ~4.66V to ~0.53V when receiving a signal (confirmed using XPR Pin 16 as GND).
  • PTT (Pin 17 / GPIO1): Keys repeater successfully when pulled low.
  • We repeated these tests using a Kenwood TKR-740 repeater with the same result — valid COOS signals present and working as expected.
  • All measurements taken directly at the repeater accessory connectors using a multimeter. RC210 was disconnected for isolation testing.
RC210 Fails to Detect COS
  • All jumpers set per manual (e.g., JP2 = 1–2 for Active Low input on Port 1).
  • GND is confirmed clean and consistent across DB9 pins 6, 8, and 9.
  • Simulating COS by shorting DB9 Pin 7 (COS IN) to Pin 6 (GND) results in:
    • No COS LED
    • No PTT trigger
    • No voltage drop on PTT OUT (Pin 3)
  • However, manually shorting DB9 Pin 3 to GND causes the PTT LED to light and voltage to drop to 0V — confirming the RC210's PTT output circuitry is working corrrectly. ** All three ports, no automatic PTT detection either **
  • Same behavior confirmed on Ports 1, 2, and 3 — no COS detection on any port.

We had this unit assembled by Mr. Ken at Arcom, and he sent it back to us in a timely manner, we also emailed him our findings as well, hopefully he can help us with this.

?

Additionally, during troubleshooting the board, we found several clipped component leads left between pads and vias. We removed these and looked over the board for any shorted traces etc. - the bigger concern remains the complete failure of COS input logic.
  • Looking for any guidance from other users in the group in the meantime.
  • Perhaps any other others of the XPR8300/8400 would also share their experiences and their pinning, we included a snapshot of our CPS Accy settings.

Has anyone else seen this issue before? Could all three COS input stages actually be defective, or are we missing a board-level config step? … We did successfully connect it to the PC softwaree but did not change any default settings, as it should have worked at least on the ?�?basic default?�? settings without changing anything correct?

?

Thanks in advance,Bryan, KB9UZO

Eastern Colorado Repeater Association-ECRA







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First thing to check for is when you power the controller on you should see one of the LEDs flash rapidly, which I recall was one of the COR LEDs then after about 5-10 seconds that should stop and then all three of the PTT LEDs should light and you will get the power up sign on message usually something like "R C 210 V something point something" "Ready". The PTT LEDs should then go out.
?
If that doesn't happen, check your power input connections, and make sure the front panel LED enable switch is on which you can check it with an ohm meter, needs to be shorting the jumper header or you can put a jumper on the LED header JP13.
?
If that is all working, set the COR and PL jumpers to the 1-2 position.? You can then ground the respective pins of the DB-9 connector, Pin 2 for PL, Pin 7 for COR.? You should get an LED light on the front panel per the respective input, if not check the diodes at D16-D21. Make sure the polarity is correct.? There is also they were mixed up with the Zener diodes since they look almost identical,? check if you can see 5231 written on them.
?
You can also set the COR and PL jumpers to 2-3 and use a known good 5-12 volt power supply to see if you can get the LEDs to light. That will prove the positive going transistors are good.

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