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Did you manage to fix this unit? There was one switching diode in the rx/tx switching circuit that seemed to fail at a fairly high rate in radios using that circuit. Unsure of its part # in your radio, but in the older Galaxy DX series (33HML, 44V, etc) it was D77, a KB362 part number. In a...

One possible explanation as to why some radios using 520's seem higher or lower in output to others of the same make/model is that not all IRF520's are created equal. You can find slightly different transconductance and on resistance specs between different 520 series parts.

Did you ever find the problem?

I have the same radio and that was the procedure.

That's what I was wondering myself, lol! If that was the case, shorted final/driver would jump to mind.

I finally got a chance to dig up my old SR490 and snapped a photo of the cap location. The fix was to add 100pf across those points.

Something else occurred to me. Years ago in the Stryker 440/490 series first gen models, there was an occasional issue with PLL unlock that displayed similar symptoms. the cure was to add a 100pfcap in parallel to another cap near the PLL chip. I'm not at the shop atm to get any better info, but...

I think you are on the right track with looking at the audio amp section. I've run into other makes/models with similar issues that traced to audio amp issues. As was mentioned, look for cap faults, especially bypass and feedback caps.

Nothing specific jumps to mind, but have you tested all PLL circuit voltages when the problem is happening? There would likely be other signal levels/voltages that are changing when this problem occurs.

Yes, this uses a multi-plexed system for frequency and channel display. The channel display is working fine. Not moving forward further with this one as the customer decided to leave it as-is.

I'm working on an S9 with controller board PCBX-0335R6 and can't seem to locate any newer info that what is posted on the CB Tricks website (that shows the 0335R. There is no frequency display, but the displays themselves test good when directly connected to a common ground and the segment pins...

I'm in the middle of trouble-shooting one of these right now with no frequency display whatsoever. if I come up with anything useful for you, I'll post an update. Update: I concur with Nomad's last pinout post. It appears to be correct. Also eliminates the displays as being the culprits in my...

I'm starting to get reports of Cobra's latest 29 Classic/Chrome series having partly blown displays, and the display Cobra is using is no longer the same as previous production versions of these radios. Does anyone know of a source for the part? I do not even have a specific part number yet, and...

You can also use some capacitor trickery to nudge the frequency up or down. To nudge up, cut a trace to the crystal and insert a cap. To nudge down, place additional capacitance across the existing tuning cap (this will reduce the affect the tuning cap has, so some experimentation is in order)...

This is an ancient thread, I know, but I wanted to post a quick update. The system discussed is very outdated, and the links no longer work as I've removed the associated files from the dtbradio.com website. I had updated the system with USB support, but due to a break-in at the shop in January...

I agree with both Nomad Coyote. Pretty much guaranteed to be an age-related issue. In your case, since AM is working well, you have a lot less circuitry to consider. Since your post didn't say anything about the receive being a problem, this limits the possibilities to the power supply and...

I know this is an older thread, but I recently had one of these come in DOA and given to the shop for parts. During a lol today, I pulled it out and did some trouble-shooting, and found that a bad ground and some loose screws were the main culprit, and got the main amp working. In this unit, the...

I just made a contact with Rocket station in Stockhom on CB channel 2, 10:16AM today, from my shop radio in Carlisle, PA.. All kinds of signal on him!

I know this is an old thread, but back about 24 years ago roughly a customer was carrying a buddy's amp across the next-door truck-stop's parking lot towards my shop for some tests, and a pair of FCC agents were in the neighborhood after investigating my shop for violations (they didn't find...

I stumbled on this IC while looking at possible diode replacements for the venerable 1N34-style part. I haven't thoroughly read through the spec sheet, but I wanted to put this out for general discussion and feedback. It claims to have a forward drop of less than 100mV, which would make for...