Cobra 29 Modulation stuck at 45%

[Shadow]

Radio Make and Model: Cobra 29LTD

PCB Number: GEPC-060-M1 (Nov 2006)

PLL Number: 29LTD 0445

Test gear available: power meter, SWR meter, modulation meter, multimeter, freq counter, dummy load

Symptoms: Radio won't go over 45% modulation even when AMC turned up or limiter clipped.

What is working: Everything else works fine

What has been tried: turned up AMC, removed limiter, power microphone

Did it suddenly happen?: Got it this way

Anything else that may be of help?: When I got it, the radio had a "swing kit", mod limiter clipped, and a MOSFET upgrade (ERF2030 w/ IRF1230)

I noticed this when the radio wouldn't swing to it's full output. It would swing about 20 watts even with the mod limiter clipped so I checked the modulation and it would top o ut at about 45%. I'm trying to troubleshoot this radio for a friend, thanks in advance!

[The Defpom]

Reduce the power output. it sounds like it is just trying to run too much power so the audio amp cant match the output to give enough drive.

[Shadow]

Reduce the power output.

Hey Scott, thanks for the fast reply. I'm not sure what you mean by reduce the power output, do you mean to adjust the AM power via the tuning slug on L14 or is there something else as well?

[The Defpom]

Yeah, the tuning slug is the way that it is designed to be adjusted by, so try screwing that slug in to reduce the output power and see if that helps.

It could just be an issue with the mosfet conversion, I have never done one (not seen the point), so I cannot help if it is something do do with that part.

[222]

likely you have checked already, but i have some stock mics that go w/that radio, that have something wrong with them, causing them to have very lo modulation. since that is unusual, i didn't realize it was those mics, for quite awhile. so just wanted to make sure you ruled out the mic. also, i don't know what deadkey you're measuring, but wouldn't a "swing to" 20w be more than 45% modulation, by default? what i'm saying basically, is are the listeners actually reporting such a low modulation level, "ear-wise", (or db wise), because i know you cannot trust readings alone. the other thing i wondered, is (excuse me if u already mentioned) if the "swing kit" is in place w/that f.e.t. mod. the reason i ask is that the swingkit deal is bad enough (in my opinion) w/the original bipolar final, but i have no idea if is compatable. i guarantee you, at least, that you don't need it in there.

jeff

[Shadow]

Yeah, the tuning slug is the way that it is designed to be adjusted by, so try screwing that slug in to reduce the output power and see if that helps.

That was it, the tuning slug was too far out, I should have thought of doing this in the first place. Thanks Scott.

and thanks for the reply 222