M1225 Repeater Build - COS Output issue

[Steve (WRDR 762)]

Hello everyone,

 

So to give a quick back story, I picked up a pair of M1225 (4 channel, 25w) units on ebay. Physically, they seem in great shape. TX/RX work on each (the internal speaker on one is a little wonky, but frankly I don't care for my use case). I have no problems writing a code plug to the unit (although, that initial setup was indeed fun!). I am trying to build these units to operate as a GMRS repeater (they are type 95A certified, I prefer to keep everything 100% legal).

 

The issue I am having is with the COS output. My understanding is that, for this to work, I need to configure Pin 8 as "PL/DPL - CSQ Detect" with output active low. I have things configured this way, but I can NOT get the RX radio to key up the TX radio. For kicks, I have also tried using Pin 4 (since it can be configured for the same PL/DPL - CSQ detect mode) and it doesn't work either. Even trying it with just "CSQ Detect", neither pin goes low when the radio receives. I have also tested this both without a mic connected, and with a mic connected that is "hung up" on the clip.

 

While squelched, pin 8 has 4.6v. While receiving (indicated by the channel number blinking AND being able to hear audio from the speaker), the voltage stays the same. The output on pin 8 does NOT go low.

 

I hope someone has some ideas, because I am at a complete loss.

 

Thanks in advance for any suggestions!

 

 

EDIT: I just went back and double checked. The two radios are behaving differently. One radio (lets call it radio A) shows 4.6v on Pin8 while squelched, the other (radio B ) shows 13.8 (the power supply voltage). They both show 4.6v on Pin4 (when configured for PL/DPL - CSQ Detect) at all times, whether squelched or not. Not sure why the two radios would behave differently. 

 

EDIT2: In case this is relevant, I was told these radios were both pulled out of a working SCADA system.

Edited October 29, 2020 by Steve (WRDR 762)

[berkinet]

Take a look at http://www.repeater-builder.com/rbtip/index.html

[Steve (WRDR 762)]

I have been looking there quite extensively. This page to be specific.. http://www.repeater-builder.com/motorola/maxtrac/maxtrac-option-plug.html . It seems to cover everything about these radios and their accessory port, and how to configure it. I have read it through a few times, but unfortunately, have yet to find any explanation for why these radios refuse to pull the output LOW when they receive a valid signal.

[Steve (WRDR 762)]

WOW! I can't believe it, but I got it working. So, it was user error (not at all shocking there!). But, in simple, the accessory connector is upside down compared to most of the other 16 pin radios. Everything I found online states that pin 1 is bottom left while looking at the back of the radio with the heatsink facing down. Apparently, this is WRONG for the M1225 (at least this version of it). I dug through the service manual and found that pin 1 is top right. I checked the ACTUAL pin 8, and guess what.. working perfectly. Hopefully this helps someone else in the future too!

 

If you are using one of the cheap, china no-name repeater cables, the blue pot for RX adjustment needs to be facing UP (towards the top of the radio). I am very thankful that plugging them in upside down didn't blow anything up, since I read online that can easily happen if these things are installed upside down.

 

Mystery solved!