Cobra 25 unhacking project

[338_MtRushmore]

I have been wanting to get a project Radio for a while. I sound a Philippine 25 with echo and variable power. Seller said it worked great, and just came back from his tech. I could almost smell the bs, so I paid $30 for it.

When I got it, I plugged it in and the channel display is mostly dead. I laughed. Called for a radio check and got nothing. I took it inside and opened her up...


I got the project I waz looking for

 

[Ghost Ryder]

I have been wanting to get a project Radio for a while. I sound a Philippine 25 with echo and variable power. Seller said it worked great, and just came back from his tech. I could almost smell the bs, so I paid $30 for it.

When I got it, I plugged it in and the channel display is mostly dead. I laughed. Called for a radio check and got nothing. I took it inside and opened her up...
View attachment 20020

I got the project I waz looking for

I would've paid the shipping and let you fix my old 23 channel Cobra 25 for free..lol. It turns on, no output. No display to go out though, its a plastic dial.

 

[Robb]

Some thoughts . . .

Recapping a radio from this era may be the first thing to consider. Clean all of the pots and switches with cleaner. Re-grease all mounted ICs with fresh heat sink compound. Think I would mount the echo board properly. I would see if it has Schottky receive diodes. Would also put HiFi TX/RX caps in it. Make sure that no coils have been mangled. If so; then restore their shapes.

Most importantly, since it has a swing kit in it, I would check it out on a scope and peak the coils for max output WITHOUT distortion. Other than that, most of those mods already in it should be OK - if tuned right. I know it can be done; been there - done that.

 

[sonoma]

like ROBB said just clean up the inside and leave the mod kit and echo in it. just mount it. more than likely the radio will work after cleaning the controls. ever time I let one of my radios set for a few months I have to clean them and lube for scratching sounds when turned.

 

[338_MtRushmore]

It is actually pretty bad. All connections for the echo board are soldered and exposed. I'm pretty sure the swing mod cap is backwards, and what is r44 doing under there?

What happened to the cap at the top left?



Tr14 is mostly missing, and more bare connections, and a damaged cap. Of course d9 is cut.


Nice coil tuning too
I promise, it has problems...

 

[Robb]

Woah; a 10v cap in the swing position?!?
I would take it out in a heartbeat, and put in a 1000uf 25v cap in its place.

 

[338_MtRushmore]

Woah; a 10v cap in the swing position?!?
I would take it out in a heartbeat, and put in a 1000uf 25v cap in its place.

Isn't the negitive side of the cap supposed to face the final also?

 

[Robb]

Yuppppp.
The negative stripe is supposed to be pointed towards the back of the radio.

BTW; does this radio has a MOSFET final; or is it a bipolar/orignal?

 

[338_MtRushmore]

It looked original. Maybe c2016, or something like that.

 

[loosecannon]

that halving of the coil over that ceramic cap used to be a pretty popular truck stop hack.
im not saying it was ever a good mod, but it was popular about 25 years ago.
LC

 

[LeapFrog]

that halving of the coil over that ceramic cap used to be a pretty popular truck stop hack.
im not saying it was ever a good mod, but it was popular about 25 years ago.
LC

I read about it in a secret cb pdf I think, isn't that coil part of a filter?

It looked original. Maybe c2016, or something like that.

Look for a 2075, or 2166. Might find a 520,1969,2078....
Yeah this is a real project radio ("easy" to restore) I bet the solder side needs some serious attention also!
I can't say I've ever seen a disc cap smashed/bent under the heatsink from factory but it could happen!

Does PA mode work by any chance?

The brown and orange wires look like a poor mans variable dead key mod, w/no transistor just a pot..
I would make her stock again and give a full alignment.
I'd bet the issues (all of 'em) are due to the crappy hackery..

You say wanted a project lol, you got one!

 

[338_MtRushmore]

I read about it in a secret cb pdf I think, isn't that coil part of a filter?

Yeah this is a real project radio! I bet the solder side needs some serious attention also!l
I can't say I've ever seen a disc cap smashed/bent under the heatsink from factory but it could happen!

Does PA mode work by any chance?

I only had about 15 minutes to look it over, and I don't know if the pa works. The solder side isn't too bad, minus a horrendous soldering job on the talkback resistor. Needs a cleaning for sure. Isn't there supposed to be a resistor on the solder side as part of the swing mod? I'll have to look into that

 

[LeapFrog]

I only had about 15 minutes to look it over, and I don't know if the pa works. The solder side isn't too bad, minus a horrendous soldering job on the talkback resistor. Needs a cleaning for sure. Isn't there supposed to be a resistor on the solder side as part of the swing mod? I'll have to look into thatView attachment 20029 View attachment 20030

You can remove the talk back, put it on a switch, or however you like, it looks pretty gnarly no doubt!

Check if two wires run from the capacitor (swing kit) to a knob up front, if that's the case it's a variable dead-key done cheaply, no resistor to be found underneath because the potentiometer is a variable resistor.

If you swing kit a 25/29 the resistor determines deadkey, insert a variable resistor and boom, variable dead key and no "usaul" resistor to find underneath the capacitor!

The TIP29,TIP31,TIP120 or many other transistor based variable dead key mod is better than just using a potentiometer. (Check RF gain pot, some mods use this and solder the two rf gain wires)

Though I don't like variable dead key /swing mods in these, the choice is always yours.
These talk fine @ 95% modulation and don't need any mods done, just a good microphone!

The real shame in this radio is the hole they drilled..... ....... The rest of the damage could be undone in an hour, that hole will last for ever.... I hate seeing lids getting drilled..

At least the solder side looks great, minus the t.b. resistor you spotted.

 

[338_MtRushmore]

I'm not sure what I am going to do with this. I already have a newer 25 with a swing mod, so I think this one might go stock, although I may keep the echo? I don't know. In the last pic of post 5, you can see where the rf gain wires are connected and bare. I thought using tape on connections was hacky, bare connections are insane.

 

[LeapFrog]

I'm not sure what I am going to do with this. I already have a newer 25 with a swing mod, so I think this one might go stock, although I may keep the echo? I don't know. In the last pic of post 5, you can see where the rf gain wires are connected and bare. I thought using tape on connections was hacky, bare connections are insane.

Yeah, the pot is probably now wired up for the variable dead key.
Can you read schematics, to find out the original part values you need to go stock?
Probably not too many values needed, one diode, one transistor, and a jumper lead?

Look over your switches on the front of the radio to make sure no tom-foolery has happened to repurpose them, any "mod" solder work should stick out like a sore thumb.