CDM1250 Low voltage beep

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emtprt
Posts: 128
Joined: Mon May 24, 2004 4:52 am
What radios do you own?: Astro Specta CDMS XTS3000

CDM1250 Low voltage beep

Post by emtprt »

We have a 2008 GMC 2500 P/U with a 45 watt UHF CDM1250 that recently has started to give a low battery beep when transmitting.
The issue is new and I had the vehicles batttery replaced and a larger alternator installed. The truck has a 200 watt siren, multiple LED flashing lights and a light bar. there is also a scanner and charger for a lightbox.

No conections have been changed, and the original A/S Mosaic antenna is still in place on the roof. The power tap is at the cable entering the under hood fuse block which is always hot and an ignition sense is inplace via a solinoid.

The beeping is irregular and occurs when running hot(lights/siren), parked or during regular driving.

I dropped the power to 30 watts today. I am considering changing the power point directly to the battery.

Has anyone else had a similar experience or a fix for my issue?

Thanks
Mark
Jim202
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Joined: Sun Sep 09, 2001 4:00 pm

Re: CDM1250 Low voltage beep

Post by Jim202 »

emtprt wrote:We have a 2008 GMC 2500 P/U with a 45 watt UHF CDM1250 that recently has started to give a low battery beep when transmitting.
The issue is new and I had the vehicles batttery replaced and a larger alternator installed. The truck has a 200 watt siren, multiple LED flashing lights and a light bar. there is also a scanner and charger for a lightbox.

No conections have been changed, and the original A/S Mosaic antenna is still in place on the roof. The power tap is at the cable entering the under hood fuse block which is always hot and an ignition sense is inplace via a solinoid.

The beeping is irregular and occurs when running hot(lights/siren), parked or during regular driving.

I dropped the power to 30 watts today. I am considering changing the power point directly to the battery.

Has anyone else had a similar experience or a fix for my issue?

Thanks
Mark

As in all initial trouble shooting, it requires pulling out the volt meter and looking around. Have you done this and tried to see just what voltage is at the rear of the CDM as well as what voltage is on the ignition control wire? You could even have a poor ground on your equipment or between the vehicle frame and the battery. There are countless possibilities on where the problem might be lurking.

On most vehicles, there is a wire that goes from the battery to the frame near the battery. I would check and see if this primary ground is working. A simple check would be to have the engine running and measure from the negative side of the battery to the vehicle frame. Have the electrical load as high as you can. This would be the headlights on high beam, the AC system running on high and the wipers flip flapping. In a good condition, the voltage you measure should be in the millivolts. If you are seeing volts, then you need to fix the ground problem before going any further.

Next while your in this high load condition, measure the voltage on the battery posts. Not the terminals connecting to the battery posts, but the actual battery posts. I have seen the battery post connections get dirty and give you all sorts of strange issues. Normally it will show it's head with alternator whine when you transmit on the radio. Next move one probe to the battery wire connection itself. Then flip the meter leads and keep the other lead on the battery post and go to the other wire connection. Your looking for a voltage difference. You can even go from the battery post to the terminal on each post to see if that connection is poor.

Next you need to do the same thing on your radio connections. Make sure you don't have a poor fuse connection, ground connection and so on. It will probably take putting the radio into transmit to see any issue show up. Some voltmeters don't like the RF from the transmitter, but the CDM is normally fairly tight and shouldn't be effected.

Hope these ideas can point you to an issue. What I didn't have you do was to start with the vehicle parked over night and measure the battery voltage. Start the vehicle and measure the battery voltage with nothing turned on. Then turn the headlights on low beam and measure the battery voltage. Put the headlights on high and measure the battery voltage. Then turn the AC on high and measure the battery voltage, leave the headlights on high. Then add the wipers. What your looking for is the roll off in voltage with the electrical load. I don't think your going to see this with having added a heavier alternator. But your just making sure the electrical system is working. You can add the light bar as a final load to your measurements. All this should be done with the vehicle at an idle.

Jim
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Bill_G
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Re: CDM1250 Low voltage beep

Post by Bill_G »

+1 what Jim said.

I've seen a hundred times where the battery ground strap to the body was bad / removed / corroded, and as more current was pulled by the other loads (lights, fans, accessories), the radio saw much less than 12V. The fix is to replace the battery ground strap to the body.

On some heavy equipment I've seen where the coach manufacturer put in a nice, heavy lead from batt neg to the frame, and then expected the body bolts and U clamps to carry that to the body. Works fine the first few years, but as the chassis ages, you start seeing a differential between batt neg and chassis ground under high load. Again the fix is to put in a ground strap.
emtprt
Posts: 128
Joined: Mon May 24, 2004 4:52 am
What radios do you own?: Astro Specta CDMS XTS3000

Re: CDM1250 Low voltage beep

Post by emtprt »

The grounding strap appears to be in good shape.
I had the original factory battery replaced and the alternator upgraded to a higher amp unit. Prior to the upgrade when the problem occurred the voltage at the radio ranged from 11.2v-12.8v depending on the load (lights, A/C, siren...).
The voltage when the truck is parked and everything is powered on presently does not drop below 12.5volts. I have swaped radios and the issue still occurs when transmitting. Could a bad antenna or SWR cause this to happen?

I am considering re-running te power directly off the battery instead of the present site where the power enters the underhood fuse block.
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Bill_G
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Re: CDM1250 Low voltage beep

Post by Bill_G »

The batt terminal of the main fuse block in the engine compartment is the preferred point.

Connect a dummy load to see if the radio reacts the same during tx.
Jim202
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Re: CDM1250 Low voltage beep

Post by Jim202 »

emtprt wrote:The grounding strap appears to be in good shape.
I had the original factory battery replaced and the alternator upgraded to a higher amp unit. Prior to the upgrade when the problem occurred the voltage at the radio ranged from 11.2v-12.8v depending on the load (lights, A/C, siren...).
The voltage when the truck is parked and everything is powered on presently does not drop below 12.5volts. I have swaped radios and the issue still occurs when transmitting. Could a bad antenna or SWR cause this to happen?

I am considering re-running te power directly off the battery instead of the present site where the power enters the underhood fuse block.


I ask you again, have you measured the voltage with the engine running at the battery? You need to start at the source and follow it back to the radio. If you don't have at least the 13.5 to 14.0 volts at the battery, why are you fighting a radio problem?

The radio is not going to function well at the low voltage your telling us about. Your high current feed for the back of the radio should not come from the under dash fuse block. You need to run that back to the battery. The ignition control can come from the fuse block.

Jim
emtprt
Posts: 128
Joined: Mon May 24, 2004 4:52 am
What radios do you own?: Astro Specta CDMS XTS3000

Re: CDM1250 Low voltage beep

Post by emtprt »

The voltage at the battery with the engine running is 13.6-13.9 volts ( No load on the system; a/c off, lights off. accessories off). The Power was picked up from the under hood fuse block feed cable connection ( prior to the block).
I ran a the feed power feed from the battery and the proplem still occurs,
thebigphish
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Re: CDM1250 Low voltage beep

Post by thebigphish »

Replacing a standard alternator with a higher output one will NOT mitigate undervolt problems, if the unit is providing voltage outside of the optimal output curve of the unit. I've seen higher current models that will provide absolute pantloads of amps, when compared to the standard issue units that will sit there and flicker a dash-warning light at a traffic light, due to the fact that the model in there now has a power output curve that is inadequate at the current idle RPM.
If the problem follows the chassis, and not that particular radio, then you most assuredly have a chassis wiring issue. Two of the three situations you described were high-current/high-load issues which may or may not be supported by the available engine RPM.

Verify the power output curve of the larger alternator, you may have installed yourself into a suboptimal situation. Granted you're talking about a unit which has a very low aggregate current load, but CDMs are finicky when it comes to voltage.
"How do you plan to outwit Death?"
"With a knight and bishop combination; I will destroy his flank.
" --Antonious Block
Jim202
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Re: CDM1250 Low voltage beep

Post by Jim202 »

emtprt wrote:The voltage at the battery with the engine running is 13.6-13.9 volts ( No load on the system; a/c off, lights off. accessories off). The Power was picked up from the under hood fuse block feed cable connection ( prior to the block).
I ran a the feed power feed from the battery and the proplem still occurs,


You keep asking for help here, but have not followed any of the comments to locate the problem you have. If you are truly wanting to resolve your problem, please start at the top of this thread and start reading through the whole thing. Print it out if you need to and check off the different steps given, but go through the steps that have been presented to you. Use your volt meter and start measuring the voltages UNDER LOAD.

If your not going to follow the recommendations on here, I doubt you will receive much further help.
emtprt
Posts: 128
Joined: Mon May 24, 2004 4:52 am
What radios do you own?: Astro Specta CDMS XTS3000

Re: CDM1250 Low voltage beep

Post by emtprt »

I am grateful for the help and responses. I have tried all of the voltage readings as described. I may not have replied correctly and appologize. We re-wired directly to battery (voltage at the battery is > then 13v per mechanic) with stable voltage under loads and without aload at idle.
A fix was found last night. The coax covering was damaged and caused a break with the copper which would intermittantly short under the headliner. The radio antenna was swapped to another location and the beeps are no longer occurring.
Thany you everyone
Jim202
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Joined: Sun Sep 09, 2001 4:00 pm

Re: CDM1250 Low voltage beep

Post by Jim202 »

emtprt wrote:I am grateful for the help and responses. I have tried all of the voltage readings as described. I may not have replied correctly and appologize. We re-wired directly to battery (voltage at the battery is > then 13v per mechanic) with stable voltage under loads and without aload at idle.
A fix was found last night. The coax covering was damaged and caused a break with the copper which would intermittantly short under the headliner. The radio antenna was swapped to another location and the beeps are no longer occurring.
Thany you everyone


If your talking about the shield on the coax cable shorting out to the vehicle body causing your problem, you haven't solved it with a new antenna cable and location. It sounds more like you have a poor ground on the heavy black wire coming from the rear of the radio. The high current return to the radio and the radio ground are both done with the heavy black wire. Yes this heavy black wire wants to go to the negative battery connection, but your comments about the antenna cable shorting out worry me. It makes me still think that you have a poor connection from the battery negative side to the vehicle frame.

The antenna coax cable should not be carrying any of the DC voltage for any device in the vehicle. If you were having issues with it, there might have been something else going on.

Jim
emtprt
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What radios do you own?: Astro Specta CDMS XTS3000

Re: CDM1250 Low voltage beep

Post by emtprt »

The shielding(ground) pinched on the rollcage and headliner wearing into the center solid copper. The center copper of the RG58 has a positional direct short with the roll cage edge and sheilding . Thesite is where the door B post and roll cage meet. I believe the door slamming may have caused the coax to migrate along with vibration and hits the headliner. On my voltmeter there is a direct short at the mini uhf center with the antenna off. The radio is currently on another NMO connector and is working without any issues
Jim202
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Re: CDM1250 Low voltage beep

Post by Jim202 »

emtprt wrote:The shielding(ground) pinched on the rollcage and headliner wearing into the center solid copper. The center copper of the RG58 has a positional direct short with the roll cage edge and sheilding . Thesite is where the door B post and roll cage meet. I believe the door slamming may have caused the coax to migrate along with vibration and hits the headliner. On my voltmeter there is a direct short at the mini uhf center with the antenna off. The radio is currently on another NMO connector and is working without any issues



Glad you have your radio up and working.

Have you learned anything through this all? What you have led everyone through here is like a doctor giving a patient an injection in the arm, but never telling what was in the injection or why the injection was given. The details are everything in trouble shooting radio and electronics problems. Leave the details out and you will spend much longer resolving the problem. Provide the details and you can be pointed right to the issue.

Jim
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Bill_G
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Re: CDM1250 Low voltage beep

Post by Bill_G »

Thanks for the update Mark. I've never heard a CDM give a low voltage beep, but it's good to know that under the right conditions they will make odd sounds. I've chased more than my share of green crimps under wet floor mats, and coax cables eaten by hidden danger in the head liner. Glad you found it.
tvsjr
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Re: CDM1250 Low voltage beep

Post by tvsjr »

You still haven't solved your problem. The radio is obtaining ground through the coax and mount. Leave the radio installed, disconnect the antenna, and see what happens. I bet the radio won't even power up.
emtprt
Posts: 128
Joined: Mon May 24, 2004 4:52 am
What radios do you own?: Astro Specta CDMS XTS3000

Re: CDM1250 Low voltage beep

Post by emtprt »

Radio powers up fine with antenna off. We replaced the coax in the original hole and covered it with protective covering this time . The old coax looks like someeone took a utility knife to it. The radio is know working properly.

Thanks everyone
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