Cobra 148 is only putting out 2 watts on SSB?

[liquidh8]

Good tip, I have to see if the sams has the washington. I need that cha rt, lol

 

[melaza]

Hi,

If R131 has been clipped, the AMC circuit shouldn't be working.

IInstall it again. Is a (10k resistor) and this one connect the base of TR-26 (AMC) to ~ 8.0 VDC. Check for TR-26 (2SC945) is on place.

If you disable the AMC circuit you gonna have a lot of problems on AM/SSB .

Have a nice day.

 

[Eastside]

Instead of waiting for someone to fix your radio for you from this forum - which is really asking a lot when you consider what is possibly wrong with it - you might instead look at the 'Service Manual' page on this forum. There is a SAMS manual for the 148GTL there. In it, it will give you a chart for each transistor and its voltages. This can help you track the problem area down yourself. May well find the circuit fault this way too.
http://www.worldwidedx.com/cb-radio-service-manuals/141891-cobra-148-gtl.html

Think I would start with the TX mixer circuit. Use the schematic on CB Tricks to find out which parts are in that circuit. Then, check the IC/transistor voltages and the diodes in that circuit.
http://www.cbtricks.com/radios/cobra/148gtl/graphics/cobra_148gtl_sch_redraw.pdf

Either do that, or send your radio to ExitThirteen or another shop and get it fixed and carefully examined . . .

Was not wanting someone to fix it for me......I was just asking for a little help.

 

[Eastside]

Hi,

If R131 has been clipped, the AMC circuit shouldn't be working.

IInstall it again. Is a (10k resistor) and this one connect the base of TR-26 (AMC) to ~ 8.0 VDC. Check for TR-26 (2SC945) is on place.

If you disable the AMC circuit you gonna have a lot of problems on AM/SSB .

Have a nice day.

Thanks for the info.....131 is still on the board...mebbe I will try pushing it back together where it was clipped and see if it makes a difference.

 

[psycho]

Yes.....its putting out 4 watts on AM....will max out at 5 watts.

Well at least the final isn't blown.

 

[psycho]

Hi,

If you disable the AMC circuit you gonna have a lot of problems on AM/SSB .
:

That is absolute bullshit. TR24 is what you shouldn't cut. R131 only opens up the AM, VR11 is what you turn up or down to get the desired SSB output. I loaf my Cobra 148s and Uniden Grants at 9 watts on ssb, I let the amp do the work.

 

[Eastside]

Well at least the final isn't blown.

Its odd....the power on AM is at 4 watts on the middle channels and drops down on the upper and lower channels...drops all the way to 2 1/2 on ch-1 and 3 watts on ch-40 and 4 swing to 5 on ch-20?

Also the meter does not work right either...it sits at 3 pds

 

[Robb]

Its odd....the power on AM is at 4 watts on the middle channels and drops down on the upper and lower channels...drops all the way to 2 1/2 on ch-1 and 3 watts on ch-40 and 4 swing to 5 on ch-20?

Also the meter does not work right either...it sits at 3 pds

Really? OK . . . You might want to re-tune the TX cans.
L47, L48, L45, L46, and L38 (in that order) in AM mode with a proper meter. DO NOT even touch L36!!! Unless you have a Spectrum Analyzer. Did you even look at the Service Manual yet?

Meters in these radios go out all of the time. I just had to change two of them this week in a couple of local operators 148's.

Was not wanting someone to fix it for me......I was just asking for a little help.

Sounds like he sent you a pretty screwed-up radio. Bought it from eBay? Complain that it wasn't 'as described'. I sure would!

 

[Eastside]

Really? OK . . . You might want to re-tune the TX cans.
L47, L48, L45, L46, and L38 (in that order) in AM mode with a proper meter. DO NOT even touch L36!!! Unless you have a Spectrum Analyzer. Did you even look at the Service Manual yet?

Meters in these radios go out all of the time. I just had to change two of them this week in a couple of local operators 148's.



Sounds like he sent you a pretty screwed-up radio. Bought it from eBay? Complain that it wasn't 'as described'. I sure would!

You have a link to the manual?

 

[Robb]

http://www.worldwidedx.com/cb-radio-service-manuals/141891-cobra-148-gtl.html

 

[Eastside]

Thanks.

Now only if I had all the test equipment and knew how to use it.

 

[Robb]

Turn the dead key down to 1 watt before you tune those cans.

This TX can adjustment will put a lot of strain on the driver and final.

Must have and use a dummy load when doing this adjustment - ESSENTIAL!

If you don't turn the dead key watts down and then run the alignment of the TX cans; you can pop the final transistor if you don't allow it to cool for 30-60 seconds between tuning each can. That is why it is best to turn the dead key down - first. Even then, let it cool before going to the next can.

DO NOT use a jewelers screwdriver! The ferrite screw inside the tuning can/will snap - they are EXTREMELY BRITTLE! You will be totally screwed if you break one; they are impossible to get out if broken. You need to tune the cans with a nylon tool; or make one out of a piece of hardwood.

Use a sine wave tone of 1000hz fed into the mic with the mic gain up 90% of the way open. Must hold the mic very steady and be very consistent! You can get a 1000hz sine wave sound file from the internet.
http://www.audiocheck.net/audiofrequencysignalgenerator_sinetone.php

Just shove the mic close to the computer speaker and tune each can in order.

DO IT ALL AT YOUR OWN RISK!

That should get you pretty close to the mark . . .

 

[Eastside]

Turn the dead key down to 1 watt before you tune those cans.

This adjustment will put a lot of strain on the driver and final.

Must have and use a dummy load when doing this adjustment - ESSENTIAL!

If you don't turn the dead key watts down and run the alignment of the TX cans; you can pop the final transistor if you don't allow it to cool for 30 seconds between tuning each can. That is why it is best to turn the dead key down first. Even then, let it cool before going to the next can.

DO NOT use a jewelers screwdriver! The ferrite screw inside the tuning can will snap - they are EXTREMELY BRITTLE! You will be totally screwed if you break one; they are impossible to get out if broken. You need to tune the cans with a nylon tool; or make one out of a piece of hardwood.

Use a sine wave tone of 1000hz fed into the mic with the mic gain up 90% of the way open. Must hold the mic very steady and be very consistent! You can get a 1000hz sine wave sound file from the internet.
Online Sine Tone Waveform Generator

Just shove the mic close to the computer speaker and tune each can in order.

DO IT ALL AT YOUR OWN RISK!

That should get you pretty close to the mark . . .

Where do you buy those plastic screw drivers...I been wanting one for a long time?

Thanks for the info.

 

[Robb]

Minute Man Electronics TV VCR DVD and Radio Alignment Tools

 

[Eastside]

$20 minimum purchase....jeez...all I want is a little plastic alignment screw driver.