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Cobra 25LTD Classic Schematic & Wiring

K

kc0mlt

Member
Jul 14, 2023
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I am working on a Cobra 25LTD Classic that has been modified in the past by the previous owner. I am trying to "restore" this back to normal so I can proceed with an alignment and tune. I have downloaded about every schematic and wiring diagram that I have found, but each one is of course some sort of variant and not the actual 25 LTD Classic. Does anyone have the actual schematic / service manual and a wiring diagram?

I am at the step of trying to figure out how to restore the wiring to the Channel 9 switch. The previous owner used it to switch the final or something.

This radio was made in August of 1989 in the Philippines.

If this isn't the correct place to post this please let me know and I will re-post in the correct forum.

Thanks
 

loosecannon said:
just to add to Nomad's post, you can still get digital copies of the original SAMS photofact manuals.

here's a link to the one for the 25GTL which is the same on the inside as the 25LTD.

SAMS Photofact manual for COBRA 25GTL SAMS # CB-207 | SAMS Technical Publishing

SAMS Photofact manual for COBRA 25GTL SAMS # CB-207
www.samswebsite.com www.samswebsite.com

LC
Click to expand...
I have a subscription to Sams and have already downloaded that model. It is not quite the same as the radio I have. I wish it was... I see on their site there is an option to buy an OEM service manual, I may just try that if no one else can come up with some sort of information for me on here.
 
kc0mlt,

Can you be specific about what is different?

I do realize that wires may not be the same color, and there may even be different part numbers involved.

Between SAMS 207 and a schematic of a 25LTD classic i think we should be able to help with your issue.
All 25LTDs are the same on the inside with the one difference being the audio chip.

Can you tell us what audio chip is in the radio you are working on?

also, you need to know what they were using the channel 9 switch for in order to put the radio back to stock. my first guess is that it was being used for talkback.

once you can confirm that the mod has been removed and the radio works as normal minus the ability to switch to channel 9 on that switch, we can move forward.
LC
 
loosecannon said:
kc0mlt,

Can you be specific about what is different?

I do realize that wires may not be the same color, and there may even be different part numbers involved.

Between SAMS 207 and a schematic of a 25LTD classic i think we should be able to help with your issue.
All 25LTDs are the same on the inside with the one difference being the audio chip.

Can you tell us what audio chip is in the radio you are working on?

also, you need to know what they were using the channel 9 switch for in order to put the radio back to stock. my first guess is that it was being used for talkback.

once you can confirm that the mod has been removed and the radio works as normal minus the ability to switch to channel 9 on that switch, we can move forward.
LC
Click to expand...
I can't really tell what Audio chip it is. I can not see any numbers on it. Just an embossed (E2) on the chip itself.

That's just the thing I have no clue what mods were done to it. I think some modulation one, because TR14 was totally removed and a wire soldered into one of the pin holes. I have one of those to put back in to make that section right, hopefully...

I have been going through it looking for anything in that section that is not correct per the print and I believe that was all they did.

As far as the wiring to the ch9 switch. it was wired back to a resistor right next to the final. They had cut on leg of the resistor and wired the switch across it. Then there was a solder blob connecting a few pins on the switch.

It's been a real party trying to figure out just what was done on this rig.
 
that mod sounds like a talkback mod.

if the radio works right now, you should be able to speak into the mic and hear yourself through the speaker with the switch in one position, and not in the other.

the only other thing it could really be is a switchable swing mod.
Basically switching that switch would change the deadkey wattage on TX.

can you take a couple of pics of the modded area of the PC board?
it will make it easier to tell you what needs to be done to remove the mod.

as for the channel 9 switch itself, it looks like they only use three of the contacts on that switch for the channel 9 function.
once you have the mods removed from it, just pick one vertical side and use those three contacts.

I can't tell you which wire to put on top and which one on the bottom but if the switch works backwards just switch them.

middle contact will go to the emitter of TR18.

one contact will go to the trace that includes the anodes of D207, D208, D209, and D210. you might find a hole in the PC board going to this trace, otherwise just solder right to the trace.

the other contact will connect to a wire coming off of the channel selector board.
I can't tell you which trace on that board the wire comes from as the schematic doesn't show that.
if you have the SAMS, it should show that wire.
hopefully in your radio you will just find a wire coming off of the channel selector board that isn't connected to anything, and that will be it.
LC
 
loosecannon said:
that mod sounds like a talkback mod.

if the radio works right now, you should be able to speak into the mic and hear yourself through the speaker with the switch in one position, and not in the other.

the only other thing it could really be is a switchable swing mod.
Basically switching that switch would change the deadkey wattage on TX.

can you take a couple of pics of the modded area of the PC board?
it will make it easier to tell you what needs to be done to remove the mod.

as for the channel 9 switch itself, it looks like they only use three of the contacts on that switch for the channel 9 function.
once you have the mods removed from it, just pick one vertical side and use those three contacts.

I can't tell you which wire to put on top and which one on the bottom but if the switch works backwards just switch them.

middle contact will go to the emitter of TR18.

one contact will go to the trace that includes the anodes of D207, D208, D209, and D210. you might find a hole in the PC board going to this trace, otherwise just solder right to the trace.

the other contact will connect to a wire coming off of the channel selector board.
I can't tell you which trace on that board the wire comes from as the schematic doesn't show that.
if you have the SAMS, it should show that wire.
hopefully in your radio you will just find a wire coming off of the channel selector board that isn't connected to anything, and that will be it.
LC
Click to expand...
Thank you fir the info / replies.

I haven't been able to get back to work on that radio yet so I will hopefully begin again here soon and look for what you all have told me.

Thanks again!
 

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