Cobra 89xlr

[Ben Hebert]

ONe leg of 2076 has 8.88 v and one other has 2.33 v.

 

[loosecannon]

glad you found one of your problems!

you still have either a shorted final or driver transistor, or a short on the traces that go to them.

re-read my last post and do the test. TR7 is the driver and TR6 is the final.
the driver will be a 2SC2091 and the final will be a 2SC2092.
they will be mounted to an aluminum wall in the radio and will be right next to eachother.

if it hasn't been posted before in the thread, here is a link to all the info you need for that radio: http://www.cbtricks.com/radios/cobra/89xlr/index.htm

be sure to look at the tech bulletin!!!
LC

 

[Ben Hebert]

When I tested bothe the driver had 14. V on two legs but the final had 14.v on only one leg so to me the driver is shorted

 

[loosecannon]

there you go.

you can replace that driver with a 2SC2314, a 2SC2091, or a 2SC1957.

the 2SC2314 will probably be the easiest to get as it's what is being used today.
LC

 

[LeapFrog]

if it hasn't been posted before in the thread, here is a link to all the info you need for that radio: http://www.cbtricks.com/radios/cobra/89xlr/index.htm

be sure to look at the tech bulletin!!!
LC

I could not find a cross reference for the dynascan part # 1sk2473/1sk2471 diodes
Can I use 1n4003 1N4148 n914?
Thank You Loosecannon!

 

[loosecannon]

you have a 'K' in the diode numbers which may be messing you up.

both diodes are regular old switching diodes, and the plain old 1n4148 will replace both just fine.
LC

 

[Ben Hebert]

just ordered both driver and final

 

[LeapFrog]

you have a 'K' in the diode numbers which may be messing you up.

both diodes are regular old switching diodes, and the plain old 1n4148 will replace both just fine.
LC

Thank you LC! I replaced the diode, and found TR-14(c458) had been clipped (God only knows why)
I don't know of a modern sub.

Trying to add 56 ohms at the base of tr-20 (A673), i'm lost.

EDIT: it's the leg towards the center of the radio! This is an older transistor the case style had me confused because it wasn't a half circle lmao

73

 

[LeapFrog]

[photo="medium"]4464[/photo] .
[photo="medium"]4463[/photo] .
After update. Time for me start my own thread..

 

[Ben Hebert]

Which final should I get

 

[LeapFrog]

Which final should I get

2SC1969, because it's rare and meant for ssb radios... j/k
2SC2078... Many could work.

 

[Ben Hebert]

I have a 2sc1969 on the way

 

[Robb]

I have a 2sc1969 on the way

Ahhhhhhhh.h..h...h....h.....h......

 

[Ben Hebert]

What?

 

[loosecannon]

leapfrog, i didn't watch the video yet, as it seems like you got it handled.
let me know if you think i should still watch it.

the 2SC458 can be replaced by a regular old 2SC945 and they have been using a 945 in this application for a long while now.
(to the gurus: yes, i know some specs are a bit different, and that the 2SC458 will perform a bit differently in some applications, but for it's uses in a CB radio; the 2SC945 will work, and the manufacturers seem to agree)

TR14 is part of the AMC circuit and was probably clipped for a modulation increase.
definitely put it back in. these radios have great audio when just tuned right.

Ben Hebert, where did you order that 2SC1969 from? 99% of the places that sell them have fakes that will never give you the power output you want.

your best bet for a final for that radio would be the 2SC2078 since it's still being produced today. If only your driver transistor was blown, then do not replace the final "just because". replace the driver, confirm that the radio is now transmitting properly, and align the transmitter section.
if you are getting more than about 16 watts PEP from a 4 watt deadkey then you are all set and it's time to put the covers back on. simply adding a 1969 final, even a real one, rarely adds any significant power, and most times part values have to be changed to optimize it for the particular circuit it's in.
LC