Cobra 25 low receive

[smoke blower]

Cobra 25 has very low receive and the audio chip gets very hot I checked a few caps any ideas what it could be I also put in a new audio chip and same thing

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Added 1 day 38 minutes 6 seconds after previous.
The radio keys up but modulation is very faint and the receive is real low and audio chip gets so hot you can't touch it. Some help would be greatly appreciated

[terryj]

Cobra 25 has very low receive and the audio chip gets very hot I checked a few caps any ideas what it could be I also put in a new audio chip and same thing

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Post Merge Complete

Added 1 day 38 minutes 6 seconds after previous.
The radio keys up but modulation is very faint and the receive is real low and audio chip gets so hot you can't touch it. Some help would be greatly appreciated

Both the modulation and the receive audio are processed by the TA7222P (IC1). If this IC is getting very hot then check the associated components to this IC. Check the caps in the output circuit, C61 could be shorted to ground, but check caps C63, C62, C67 and C168. Check for the correct voltages on IC1.
If you don't have a schematic you can get one from here: https://www.worldwidedx.com/threads/cob ... ic.141820/

[smoke blower]

I will check those out and see what I find I already checked a few around the audio chip . Thank you for helping I will let you know when I get these checked y

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Added 8 hours 15 minutes 58 seconds after previous.
I can't find c62 or c168

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Added 15 hours 41 minutes 26 seconds after previous.
I have looked the schematic over and the parts layout and I am having a very hard time finding c62 or c168

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Added 9 hours 54 minutes 58 seconds after previous.
I have been over this board serval times I don't see a C72 or C168

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Added 5 hours 11 minutes 20 seconds after previous.
Man it would be nice to have someone help me with this . This is why I haven't donated to the forum you just can't get any help it takes weeks before you might get a reply

[MDYoungblood]

I don’t know a lot about the 25 models and not sure which one you are working on. Looking at a schematic of a GTL, it looks like C62 is just off pin 6 of the audio chip, like you I couldn’t find C168, I think that is in the 29 models. If the chip is getting extremely hot, that is telling me it is being over volted. My guess is the modulation limiter has been clipped or the transistor has gone bad.

3’s

Greg

[smoke blower]

The final transistor was ad I pulled it out and tested it and it was shorted. As of now I put in a new one and the radio will key up but very little audio and the audio chip still gets very hot

[terryj]

If the audio IC is getting very hot that means it is drawing to much current. On the TA7222 pin 1 is the voltage in, it should be at your supply voltage. Pin 4 is your audio input an pin 9 is the audio output, this is connected to the collectors of both TR7 (2SC2078E Final) and TR8 (2SC1957Q Pre-Driver) via the modulation adjust VR5.

Somewhere in the output circuit something has changed enough to load the output and draw down the transmit and receive audio. Check C154 it is in series with R118 and connects to ground.

I think is is a much better schematic: https://www.cbtricks.com/radios/cobra/2 ... td_sch.pdf

[Tinkerjim]

I'd check the rx/tx switching transistor s
There should be 8 volt s on the collector
On one in rx and 0 volts on tx if it is shorted
It's not fully going into rx. Still in tx even unkeyed... These transistor are generally in the right front corner of the pcb.
I'll have to look at schematic to get the tr number..

[Tinkerjim]

Tr16 is the switching transistor
Check collector ( center pin)
For proper voltage.

[smoke blower]

Thank you I appreciate it I will get it checked out and let you know what I find.

[Slowdraw]

Very little doubt to me that the output transformer has shorted windings. Happens sometimes when the final shorts out. Replace the transformer if you can find one. May have to replace the audio IC. Sometimes they both short out due the load of the shorted final and shorted turns in the transformer. Fairly common problem.