CDM-1250 won't shut off with ignition

[ka7wnf]

I have a CDM-1250 in my work truck that has developed an annoying problem. Nothing was changed prior to it's doing this. The radio will turn on with ignition sense but it will not shut down. I have verified that the power to the radio goes off with the key. An MCS-2000 wired to the same power source works fine. Sometimes it will shut off then turn itself back on a few seconds later. If I don't manually turn it off it runs the battery down. I did have a new battery installed a few weeks ago but I can't recall if this started before or after that. I just never checked the radios to make sure they actually stayed off. Any ideas?

[jackhackett]

You'll first need to check if it's a problem with the radio itself or with the ignition sense connection point.

With the key on, try to switch the radio off and on by disconnecting and reconnecting the ignition sense lead. You want to actually break the connection completely rather than just switching the key off and on.

If the problem still happens it's most likely something in the radio. It may have gotten a surge when the battery was replaced.

If it works okay that way, there may be some residual voltage or noise on your ignition sense connection point. Check the voltage with a voltmeter, not a test lamp. I've seen guys use a lamp to find an ignition connection only to have the radio stay on... when checked with a meter it shows a smal voltage that isn't enough to light the lamp, but is enough to hold the radio on.

[ka7wnf]

Good advice, I'll try that. It does act like something could be backfeeding it, although the MCS ignition sense comes from the same source and it works like it's supposed to.

[fineshot1]

I don't know why but over the last few years i have seen about 5 or 6 CDM1250's
come to me with ignition problems and all of them had to go back to moto to
have the ignition sense circuit on the main board repaired. Seems to be vulnerable
to severe spikes or transients and not very robust. I even went so far as to open
up the radio and observed some of the smt parts scorched on the pcb assembly.

[Bill_G]

I don't know why but over the last few years i have seen about 5 or 6 CDM1250's
come to me with ignition problems and all of them had to go back to moto to
have the ignition sense circuit on the main board repaired. Seems to be vulnerable
to severe spikes or transients and not very robust. I even went so far as to open
up the radio and observed some of the smt parts scorched on the pcb assembly.

Interesting. I haven't experienced it with CDMs (yet), but have a lot of experience with the ign sense circuit burning up in other mfgs products in 12V Ford vans converted to Lift bus service. I speculated something on the line went negative enough during turn off to burn the lightly spec'd protection diodes in these boxes, but not deep enough to burn a Spectra. So, I added diodes with greater PIV in line, and that solved it. It could be a relay or a motor on the bus with a bad or missing suppression diode, and I knew I couldn't expect the mechanics to find it. It randomly occurred across the fleet and could not be duplicated or confirmed except by service records. So, I campaigned the fleet. Brute force with a blunt object. Maybe the CDM needs a diode in series on the ign sense line as part of it's SOP.

[ka7wnf]

Okay, I found the problem and fixed it. It wasn't the CDM's fault, well not entirely. For as long as I've had this truck, (middle of last year) the CDM has been slow to shut off. 10-15 seconds. I figured they were just that way. Until it began staying on.

I discovered that the ignition sense would drop to 2 volts with the key off and then slowly trickle down to .5 volts. So something was back feeding it. I tore into it today and discovered that it was getting power off an accessory power switched relay and the load was shared with a siren unit. I pulled it off that relay and switched it over to another one that also powers a 2 meter radio. That cured it somewhat but it was still very slow to shut off.

So I switched it over to a second relay that provides ignition sense only to the MCS and CDM and the other relay powers only a 2 meter radio and the siren. All is good and now the CDM shuts off almost instantly and stays off.

What did we learn from this? The CDM radio seems to be very sensitive to ignition sense voltage levels and it doesn't like to share it's power sources. I'm guessing that the siren head had some capacitors in the B+ that slowly bleed down and that was keeping the CDM on.

[Bill_G]

Common enough problem. We often put in a relay switched by ign/accy with the radio A+ on the hot side, and radio ign sense on the switched side so that they are as close to the same potential as possible.

[jims123]

Here is my foot on this issue it have been hard one for me and other,,, I have seen this and tested 12.5 vdc enter pin 10 in accessory connector or J501 will pass VR510 zener diode also R510 both in parallel form there will get to R 530 AND TP530. On TP 530 you must read 12.01 if your power supply is set for 12.5 vdc, the circuit if futher isolated by D661 to prevent false start-up. The only part will make this false will be emegency start up pin 9 it get is 12.5 vdc form the radio it self thru R541..