Motorola CDM1250 Dead Short

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erickirchey
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What radios do you own?: CDM1250 APX7000 APX7500

Motorola CDM1250 Dead Short

Post by erickirchey »

Hey guys one of our radios in the command vehicle has died! I am pretty good with electronics as i used to fix flat screen tvs in my previous life lol
I was wondering if there are any common problems where this would happen and where maybe to start looking i have already taken the radio apart and do not see any signs of toasted parts when i hook a volt meter to the 12v pig tail it shows a dead short radio worked last time the truck was used but its been some time and they did not turn off the battery master switch the last time they used the truck so the battery's drained like they should since we got a new command vehicle and now we are needing it for a second EMR truck I would like to see if i couldn't fix this radio for fairly cheap since you can buy them fairly cheap used of ebay I dont think we want to throw a bunch into it.
Thank you
One thing that's great about firefighters: If they don't have the equipment they desperately need, they don't have the help, they don't care. They'll do it on their own.
RFguy
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Re: Motorola CDM1250 Dead Short

Post by RFguy »

My guess: The trucks battery was hooked up backwards and the protection diode in the radio is shorted.
erickirchey
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What radios do you own?: CDM1250 APX7000 APX7500

Re: Motorola CDM1250 Dead Short

Post by erickirchey »

is that the silver disc looking component on the underside of the 12v pigtail?
One thing that's great about firefighters: If they don't have the equipment they desperately need, they don't have the help, they don't care. They'll do it on their own.
erickirchey
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Posts: 5
Joined: Sat Dec 12, 2015 6:18 pm
What radios do you own?: CDM1250 APX7000 APX7500

Re: Motorola CDM1250 Dead Short

Post by erickirchey »

I ordered the Protection Diode MR2835 when it comes in I will post the results! I have the feeling one of the guys hooked up the 24 volt jump pack to the truck!
One thing that's great about firefighters: If they don't have the equipment they desperately need, they don't have the help, they don't care. They'll do it on their own.
erickirchey
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Posts: 5
Joined: Sat Dec 12, 2015 6:18 pm
What radios do you own?: CDM1250 APX7000 APX7500

Re: Motorola CDM1250 Dead Short

Post by erickirchey »

Well guys got the part in could not find the exact some part number but I did find one on eBay Over-voltage Transient Suppressor 23V 62A MR2835SK and it worked out great radio is back in full working order thank you for pointing me in the right direction!

http://www.ebay.com/itm/172016301787

For those of you tackling this task on your own this is a surface mount part you will need a hot air re-flow station or in a pinch with extra caution a heat gun.
One thing that's great about firefighters: If they don't have the equipment they desperately need, they don't have the help, they don't care. They'll do it on their own.
erickirchey
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Posts: 5
Joined: Sat Dec 12, 2015 6:18 pm
What radios do you own?: CDM1250 APX7000 APX7500

Re: Motorola CDM1250 Dead Short

Post by erickirchey »

Well the problem is back again.... Same protection diode shorted any guess as to why this keeps happening?
One thing that's great about firefighters: If they don't have the equipment they desperately need, they don't have the help, they don't care. They'll do it on their own.
codefoxed
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Re: Motorola CDM1250 Dead Short

Post by codefoxed »

I'd say either faulty diodes (poor quality / counterfeit) or an electrical system fault on the vehicle causing excessive power spikes on the radio's power supply.

Bad or dying vehicle battery (which would have a high resistance and possibly allow the voltage to float higher with the engine running)?
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Bigred
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Re: Motorola CDM1250 Dead Short

Post by Bigred »

Had a Maxtrac once eating diodes. Was on a short bus with a wheelchair lift. The radio was wired too close to the lift solenoid. Re-routing power to battery fixed that.

Anything funny going on with your vehicles electrical?
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RFguy
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Re: Motorola CDM1250 Dead Short

Post by RFguy »

Bigred wrote:The radio was wired too close to the lift solenoid.
That solenoid is the smoking gun. I bet that solenoid didn't have a protection diode across the coil to dampen the huge reverse voltage spike that will come off that thing when power is removed from the solenoid coil. It's a common problem with vehicle outfitting. We only ever use relays/solenoids with protection diodes. They they don't have one, we add one.
KE7JFF
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Re: Motorola CDM1250 Dead Short

Post by KE7JFF »

I'm curious where you have the power pigtail plugged in from the battery?
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Jim202
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Re: Motorola CDM1250 Dead Short

Post by Jim202 »

Sounds like you need to have a head to head talk with who ever is maintaining this vehicle and ask how they are jumping the dead batteries on the vehicle.

Is it possible they are using the 24 volt pack as a regular practice like you said happened once?

Is it possible that the battery terminals are not clearly identified as to which is positive and the person trying to charge them is connecting the charger up backwards?

It also looks like additional training is needed for who ever is driving the vehicle to insure that when the vehicle is shut down that the battery switch is in fact turned off. Maybe a check list of the steps to take in starting and parking the vehicle are in order. These command vehicles are very involved with the many steps that need to be taken to go from parked to on road and again from on road to back in the garage location and shut down.

Having been in many of these command vehicles, the connections going to the radio equipment can be controlled in a number of ways. With out additional information on how your vehicle is configured, it is hard to offer any suggestions. But if the same radio has been damaged multiple times, it's in your best interest to investigate how it's wired and why the problem keeps occurring. I am surprised that other radios are not being effected with the same problem.

I didn't see in your post where this radio was used or how it was powered. Is it being used up front for the driver? If so, is it connected to the normal vehicle engine power feed? With poor batteries, it is possible that the vehicle starting motor is the culprit causing the problem here. I am going to stick my neck out on this one and guess that if this is the case, the vehicle battery system is old and the resistance of them has gone high. This is normal with age. But the indications show up by having a problem starting the vehicle. Like it won't crank or cranks slow.

If the batteries are around 3 years old or more, you need to replace them. As automotive batteries age, their internal resistance starts to go up. They no longer can hold the cranking capacity that they should. When the engine is running, you start to see spikes and or voltage changes that are effected by the load being applied. Like the headlights and air conditioning. You could even have an alternator problem where it's not charging correctly and putting out too low of a voltage or too high of a voltage. Corrosion on the battery terminal connections can drive an electrical system crazy.

A digital volt meter is your best friend. Need to get under the hood so to speak and try to figure out what is going on. There have been many threads on here about how to check the correct operation of the vehicle alternator, so I am not going to sit and go through that again.

But if you haven't already identified what is causing your problem, you need to supply some details for any one on here to be of much help.

Jim
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