Backlight not working on CDM1250

nmfire10 · Post by **nmfire10** » Tue Jul 18, 2006 7:37 am

Here's a new one. The display and button backlighting on my CDM1250 seems to have stopped working. I've changed the backlight setting with the CPS and function buttons to no avail. Any ideas?

bnn121 · Post by **bnn121** » Tue Jul 18, 2006 9:04 am

I've seen this happen with remote heads...The display board inside the housing comes loose...after converting it from a dash mount to a remote mount. The board just snaps in...no screws.

If this a dash mount...you still may want to check and make sure the board is seated correctly.

nmfire10 · Post by **nmfire10** » Tue Jul 18, 2006 10:34 am

It's a remote mount and it happened right after I had the control head removed and bouncing around my truck while redoing things. Sounds like the culprit.

Once the temperature outside today is less than 100 degrees, I'll take a crack at it.

Wile E. Coyote · Post by **Wile E. Coyote** » Tue Jul 18, 2006 12:00 pm

I have seen this before, along with loss of on/off control. In our case, it was due to loss of FLT_A+ to the control head. I found that there is a fuse INSIDE the PCB that feeds the control head, and there is a note about it in figure 4-13 (page 4-19) of the detailed service manual. it reads:

Note: fuse is part of PCB. In case fuse is blown, replace it with R0410 P/N 066257B47

Good Luck and I hope this helps,
~WEC

nmfire10 · Post by **nmfire10** » Wed Jul 19, 2006 11:47 am

Now that you mention it. The power button also doesn't work with the radio is off. Can this also be a result of the board being dislodged? If it is the fuse, how can I fix it without ordering parts from motorola?

Wile E. Coyote · Post by **Wile E. Coyote** » Wed Jul 19, 2006 12:59 pm

It's been a little while, but I believe it's nothing more than a 0Ω surface mount resistor. Just about anything will work. I just checked and that Motorola part is no longer available anyway.

nmfire10 · Post by **nmfire10** » Wed Jul 19, 2006 2:59 pm

So, for me, that means make a little piece of wire into a jumper. Where the hell am I going to find this thing if it is in fact blown?

Wile E. Coyote · Post by **Wile E. Coyote** » Thu Jul 20, 2006 4:53 am

I just cracked open a low power VHF version, and I found R0410 on top of the main PCB near the jack that connects to the control head (J0401). It is the only one light in color. If you don't have a detailed manual, let me know what model you are using, and I will try to scan the location & post it.

FYI - Looking at the Circuit board wiring diagram in the book, it shows a trace simply shorting out that resistor/fuse. Looking at the real thing, that trace is missing. I think your wire jumper will be OK.

~WEC

edit - location correction

nmfire10 · Post by **nmfire10** » Tue Aug 01, 2006 1:15 pm

I'm not seeing it. Which one is it?

nmfire10 · Post by **nmfire10** » Tue Aug 01, 2006 1:25 pm

now that i look at my own picture, i see it... the light colored one to the rear of the control head connector.

HOW IN BLOODY HELL AM I SUPPOSED TO DO THAT! The thing is smaller than an ant. My soldering iron's tip is bigger than that thing.

nmfire10 · Post by **nmfire10** » Tue Aug 01, 2006 2:16 pm

OK. In the process here, I managed to remove the 'fuse' and the surface mount component next to it since i don't have the right tools for this. No possible way i could fix either one of them. I figured i was screwed.

I plugged it back into my truck to see what was broken now. IT WORKS PERFECT. I'm not going ask, i'm just going to nod my head and smile.

jackhackett · Post by **jackhackett** » Wed Aug 02, 2006 12:34 pm

I believe what you removed were a couple of bypass caps.

The fuse is visible in that close up picture, if you look at the line of components below the connector, under the second one from the right you will see two pads where another chip component could go, and a circuit trace comes out of the top one, makes a u-turn and connects to the bottom one.

THAT is the fuse, and the solder pads are where you would put the zero ohm jumper (R0410) if the fuse were to blow.

Since it has started working again, I would guess your problem was probably a bad connection to the head, either the cable or the control head board not seated well.

Also, when dealing with those little chip parts, I find a good Weller solder station with a small screwdriver type tip combined with a good magnifier and a steady hand are all you need to replace them.

nmfire10 · Post by **nmfire10** » Wed Aug 02, 2006 8:03 pm

I'm not following what you are pointing at. If you have a second, could you mark on the picture what i should have fixed?

jackhackett · Post by **jackhackett** » Thu Aug 03, 2006 2:44 am

Ok, see the screw hole in the middle of the picture? From the top of the gold area around it go straight to the right, past the two little black chips, see that trace shaped like a squared off C going between two bits of solder? That's it.

nmfire10 · Post by **nmfire10** » Thu Aug 03, 2006 4:50 am

Oh. So there is no 'fuse' then if there is just a trace around where it would have been.

What I messed up is above and to the left of that. See the really tiny surface mount whatevers. There is a light grey one and a black one to the right of it. Those two are no longer there.

jackhackett · Post by **jackhackett** » Thu Aug 03, 2006 7:11 am

In this case they are using the trace as a fuse, and they provide a place to put a jumper in case the trace fuse were to blow.

As far as I can tell those part you removed are bypass capacitors, used to filter some of the leads going to the connector. I don't know that it will have any effect on the functioning of the radio, probably more to limit emissions to meet FCC complience.

Wile E. Coyote · Post by **Wile E. Coyote** » Thu Aug 03, 2006 7:37 am

jackhackett wrote:In this case they are using the trace as a fuse, and they provide a place to put a jumper in case the trace fuse were to blow.

I would agree. I just compared my books and radio with your photo, and you must have a newer version where they did away with the surface mount component and added the trace. My appologies if I pointed you into the wrong direction. However, I am glad that it is working for you now!

~WEC

nmfire10 · Post by **nmfire10** » Thu Aug 03, 2006 12:46 pm

Ok. This is so typical of me. I set out to fix something. I break it even more. I find out the problem was something else and I now have two broken things. And it starts working fine despite all that.

kcbooboo · Post by **kcbooboo** » Thu Aug 03, 2006 1:39 pm

Maybe you're in the wrong line of work?!?!?!

I know how it feels, and I'm in the RIGHT line of work. Happens to all of us. Definitely elicits some "expletive deleted" remarks.

Bob M.