CDM that always requires ignition sense

[Jay]

I've got a new (to me) CDM1550 VHF radio. Fairly recent firmware (R05.05.19) and is a full featured (DP6AN) model.

The radio will not power up without pin 10 having 12v on it...Regardless of what setting I choose in the CPS. Anyone ever seen this before? In addition, there is no backlight of the control head, including tx/rx LEDs. I've tried multiple control heads, so the issue is not in the head.

Other than these two strange behaviors, it transmits and receives fine.

Thanks,
Jay

[fineshot1]

Try shorting accessory pins 7 & 9 together and applying power to the main
power cable - radio should power up for you.

As for your problem, yes i have seen this before but only on CDM radios that
had the ignition sense detection circuits wacked with more than 15V and actually
burnt some smt parts on the main board.

[Jay]

Well, I will give it a shot...But what is your logic between shorting those two pins? Yes, I figured there was some component damage that was causing the head not to light up.

Jay

[fineshot1]

Well, I will give it a shot...But what is your logic between shorting those two pins? Yes, I figured there was some component damage that was causing the head not to light up.

Jay

Jay - the shorting of those two pins in an un-documented method of powering
up the CDM's. It has worked for me before unless you have a brand new radio
and motorola made some change i am unaware of. It is also documented on
some of the threads here on the batlabs forums, do a search and you can find
them all. Good luck and let us know how you make out.

[Motoboy]

Shorting pins on the CDM to make the radio power up will work, but it is a hokey way of accomplishing ignition power-up. I have run into several instances of An-other radio shop doing this, and then all of a sudden the radio dies. In early-model CDM's there was a diode kit that needed to be installed with ignition sense kits to suppress spikes in the ignition sense line. If those spikes entered the radio on the ignition sense line, they would either blow the diodes that couple the on/off control signals to the logic circuitry, or they would blow the microprocessor.

Jay, it sounds like D0660 diode on the main board is blown on your radio, which is responsible for passing the logic from the on/off switch.

Fineshot1, shorting pins 7 (ground) and 9 (emergency input) will give no noticeable effect to the CDM user, though it will eliminate a "bonk" tone on power-up if you have a Maxtrac that is not programmed for emergency. In order to give the desired effect that you speak of, you will need to short pin 13 (A+) to pin 10 (ignition sense). However, if a spike comes in on A+, it will go directly to ignition sense in, and it will cause problems as detailed above.

Shorting the ignition sense on CDM's is one of my MAJOR pet peeves. It is an installation problem that requires a bench fix, and it is 100% preventable

[RF_Burns]

I always wished they would have used the same Ign sense logic as they did in their in-car cellphones. In the cellphones the ign sense line was held high by a weak pull-up resistor. Just applying power and the phone would turn ON. If you wanted Ign control, wiring ign sense pulled the line low when the ign turned off.

Having to add the little fragile option connector and wires was just a headache in those applications where radios are moved around alot.

[Bigred]

Shorting pins on the CDM to make the radio power up will work, but it is a hokey way of accomplishing ignition power-up. I have run into several instances of An-other radio shop doing this, and then all of a sudden the radio dies.

The radio dies? Why? When you hook up an external speaker to a CDM the 7-9 jumper is there in the connector. I've never seen a warning to remove it to prevent a CDM from dying! I have found that the only way that a CDR500/700 will recover from a complete power outage is to have the 7-9 jumper in, no matter what the ignition sense is programmed to and the ignition wire hooked up.

[fineshot1]

Shorting pins on the CDM to make the radio power up will work, but it is a hokey way of accomplishing ignition power-up. I have run into several instances of An-other radio shop doing this, and then all of a sudden the radio dies. In early-model CDM's there was a diode kit that needed to be installed with ignition sense kits to suppress spikes in the ignition sense line. If those spikes entered the radio on the ignition sense line, they would either blow the diodes that couple the on/off control signals to the logic circuitry, or they would blow the microprocessor.

Jay, it sounds like D0660 diode on the main board is blown on your radio, which is responsible for passing the logic from the on/off switch.

Fineshot1, shorting pins 7 (ground) and 9 (emergency input) will give no noticeable effect to the CDM user, though it will eliminate a "bonk" tone on power-up if you have a Maxtrac that is not programmed for emergency. In order to give the desired effect that you speak of, you will need to short pin 13 (A+) to pin 10 (ignition sense). However, if a spike comes in on A+, it will go directly to ignition sense in, and it will cause problems as detailed above.

Shorting the ignition sense on CDM's is one of my MAJOR pet peeves. It is an installation problem that requires a bench fix, and it is 100% preventable

I fail to so how it is "hokey" if the op has tried every other method and has failed to power up the cdm radio.
I gave the op a last known method to get the radio to power up which is what he asked for and it does work
most of the time and I have done it many times with ignition sense damage on cdm radios.

[Jay]

Well, I can report that shorting pin 7 and 9 in this particular radio does power up the radio. The radio will stay powered up after my jumper is removed from those pins as well.

Yes, I'd like to fix the actual problem, and not just put a band aid on it...But it is a good troubleshooting technique to know, from my perspective.

Motoboy, where is D0660 located, and do you happen to know a part number? I assume this fixes only the issue with it powering up and not the no backlight or tx/rx LEDs.

Jay

[Motoboy]

Sorry about the tone of that post. I could have been a little more tactful there.

The radio dies when it gets a negative voltage spike, usually from a heavy-duty power solenoid (e.g. ignition solenoid in a semi or bus). This negative voltage spike exceeds the PIV rating of the diode, and the diode usually opens. When the diode does not open, this spike goes to the CMOS microprocessor, and if it jumps even one metal-oxide junction the result is fatal. The diode kit (HLN6325) is designed to short this spike to ground before it enters the radio.

Jay hit the nail on the head. It is best to fix the radio right instead of putting a band-aid on it. I have a friend that works in the HVAC industry, and he had to go out once to look at a direct-fired burner unit that started the filters on fire in the plenum next to the burner. Turns out the unit's blower fan had worn and loose belts that were causing low airflow. Instead of replacing the belts for $100, they jumpered out the airflow switches to make the burner run. Without enough airflow, the flame sucked back into the return air plenum. The moral of the story is that it pays to fix the radio right!

D0660 is located on the top of the board (the side you see when you take the cover off). If you locate the wide ground trace between the power connector and the accessory connector, follow it up to a screw hole, then to the left (looking from the back of the radio). If you look above that trace (towards the front of the radio), you will see a large capacitor (47uf, the package should say "476" on the top). There are two 3-legged diodes there (they look like transistors, but are actually dual diode packages) to the left (again looking from the back of the board). The one closest to you is D0660, which passes the logic from the on/off switch, and the other is D0661, which passes ignition control. Both dual diode packages (all four diodes) have their cathodes tied together, which is why they all blow when they see a negative voltage spike. Part number for both is 4813833C02, and they are available from Motorola for 36 cents each. You will also need a steady hand and a hot iron. By contrast, the HLN9242 accessory kit is $16, or about 45 times more expensive for the band aid than to fix it right.

I owe a sincere apology to Fineshot1. Turns out the emergency input on the CDM includes a "wakeup" feature, so if there is an emergency switch closure, the radio will turn on and revert to emergency. If the radio is not programmed for emergency, this will work fine, and would theoretically be safer than jumping to the power source. If the system the radio is on includes Emergency operation, though, this would be detrimental... But good to remember when working on a CDM or CDR700.

[wavetar]

I do believe jumpering pin 4 to pin 10 works as well...just have to set the pin 4 as alarm output active low in the CPS. When power is applied to the radio, pin 4 goes high to 12-volts, and feeding that into pin 10 'fools' the radio into thinking ignition is applied. Then the emergency pin can be used for it's intended purpose, if desired.

And as far as the actual problem with the radio, I can almost guarantee someone tried to wire the radio directly to 24 volts...or at least the ignition pin.

Todd

[fineshot1]

I owe a sincere apology to Fineshot1. Turns out the emergency input on the CDM includes a "wakeup" feature, so if there is an emergency switch closure, the radio will turn on and revert to emergency. If the radio is not programmed for emergency, this will work fine, and would theoretically be safer than jumping to the power source. If the system the radio is on includes Emergency operation, though, this would be detrimental... But good to remember when working on a CDM or CDR700.

No apology is necessary and I am always pleased to share info I have learned(mostly from batlabs forums)
with other forum members here and elsewhere.

Also - thanks for that part number and location info.