Batboard

I'm a newbie, so please be patient with me. I have a small fleet of school buses equipped with CDM 1250 radios. Some info from the box is "CDM1250 136-174 25-45 W 64 CH" and "AAM25KKD9AA2AN" .
One bus is a small 20 passenger with a light duty battery. If the radio is left on over a 3 day weekend, the battery will be too low to start the bus. It usually has a couple of different drivers and they don't always remember to turn the radio off. The bus has ignition sense and had worked until about a year ago. There is power on the ignition sense cable to the radio, but the radio doesn't turn on and off with the ignition key. The motorola guy reprogrammed all school district radios for some different frequency requirements. When asked about it, he confirmed that the ignition signal is getting to the radio, and that the ignition sense feature was enabled in the programming. He said that about the only thing left was a bad pico fuse in the radio (not sure if I'm spelling pico correctly). He said that Motorola's bench charge is $309 plus whatever repairs are necessary. That brings me to my question: can the radio be opened and the pico fuse be changed? If so, does someone have instructions, pictures, etc? I have a friend who has done repairs on circuit boards and has the skills to solder a new fuse (or whatever may be required).
The radio is still functional as it is, but it would sure be nice to have the ignition sense functioning properly. Thanks and have a nice day.

JoeBo wrote:I'm a newbie, so please be patient with me. I have a small fleet of school buses equipped with CDM 1250 radios. Some info from the box is "CDM1250 136-174 25-45 W 64 CH" and "AAM25KKD9AA2AN" .
One bus is a small 20 passenger with a light duty battery. If the radio is left on over a 3 day weekend, the battery will be too low to start the bus. It usually has a couple of different drivers and they don't always remember to turn the radio off. The bus has ignition sense and had worked until about a year ago. There is power on the ignition sense cable to the radio, but the radio doesn't turn on and off with the ignition key. The motorola guy reprogrammed all school district radios for some different frequency requirements. When asked about it, he confirmed that the ignition signal is getting to the radio, and that the ignition sense feature was enabled in the programming. He said that about the only thing left was a bad pico fuse in the radio (not sure if I'm spelling pico correctly). He said that Motorola's bench charge is $309 plus whatever repairs are necessary. That brings me to my question: can the radio be opened and the pico fuse be changed? If so, does someone have instructions, pictures, etc? I have a friend who has done repairs on circuit boards and has the skills to solder a new fuse (or whatever may be required).
The radio is still functional as it is, but it would sure be nice to have the ignition sense functioning properly. Thanks and have a nice day.

If the shop your using is charging you $309 for a bench charge, you need to find another shop. Changing out the pico fuse is only about 15 minutes. It takes more time to get the case covers off and back on than it does to change the fuse.

The fuse looks like a very small resistor. Problem is it is surface mounted, so it takes some special soldering skills and the hot air soldering iron to do it the right way.

It sounds like the radio shop is sending the entire radio back to the depot for service. When they come back, the radio shop will have to re program the frequencies back into the radio.

My other concern is with the radio killing the battery over the weekend if the driver fails to shut it off with the volume control, that tells me the radio tech had to set the software setting in the radio to do that. Not a smart move. The concern I have is why the fuse is blowing in the first place. This is not normal. I would suspect that the high current feed to the radio might have a bad connection. When the radio transmits, the fuse blows because it can't supply enough current in transmit. Think that pico fuse is only like a 2 amp rating and not large enough to hold the TX current.

Jim

The ignition sense circuit is protected with a couple of diodes, not a fuse. Fusing of the ignition sense circuit is accomplished with an inline fuse adapter. Flat rate on a CDM at full list price is $284 and includes all time & materials. So your Motorola guy doesn't know what he's talking about.

For transit buses, I don't like ignition sense. A low voltage disconnect with a timer like a Havis Chargeguard is great. Let's you keep the radio running for a predefined period of time after the ignition is killed, plus provides low voltage and over voltage protection to the equipment. Only problem is they're a bit expensive. Well worth the investment when it saves your battery or radio from a premature death.

escomm wrote:The ignition sense circuit is protected with a couple of diodes, not a fuse. Fusing of the ignition sense circuit is accomplished with an inline fuse adapter. Flat rate on a CDM at full list price is $284 and includes all time & materials. So your Motorola guy doesn't know what he's talking about.

For transit buses, I don't like ignition sense. A low voltage disconnect with a timer like a Havis Chargeguard is great. Let's you keep the radio running for a predefined period of time after the ignition is killed, plus provides low voltage and over voltage protection to the equipment. Only problem is they're a bit expensive. Well worth the investment when it saves your battery or radio from a premature death.

There is a pico fuse on the main board that I thought feeds the SW B+ circuit. If the fuse goes, you can't power up the radio.

Jim

I've had other bus devices - particularly outboard air conditioners and blowers - blow the internal fuse on some radios. After the key turns off, a deep negative spike (on the order of -50V) runs down the switched power circuit in the vehicle clobbering anything that doesn't have good PIV protection. Usually it is an intermittent problem that maintenance is never able to locate. If the CDM fuse is in fact blown, have it replaced, and then put a much smaller value fuse (like 2A) in the ign sense lead to the radio so that it becomes the sacrificial part. If that external fuse starts blowing in a regular basis, you at least know that vehicle has a problem. But, you can prevent the fuse from blowing by inserting a rectifier diode in line that has a PIV of at least 100V. You should also consider putting a master battery switch in to preserve the batteries. They are not that expensive. But, it does mean that everyone has to remember to turn them off at the end of their run.

I am under the assumption that OP's radio is powering on, but that the ignition sense function is not working. I don't see how the programmer could confirm the radio has ignition sense in the codeplug or the batteries are dying over the weekend if the radio isn't powering on.