Pro-651: Low audio on FM modulation.

HudsonScannerGuy · May 5, 2018

I recently acquired a PRO-651 from a local in town and I discovered it had low audio on FM, but AM modulation seems fine. How do I fix this? Is it a speaker problem? Is it an internal/DSP problem? How do I go about repairing something like this? Does it need to be taken apart? Do I need a new component? Any help would be appreciated. Thanks

iMONITOR · May 5, 2018

HudsonScannerGuy said:
I recently acquired a PRO-651 from a local in town and I discovered it had low audio on FM, but AM modulation seems fine. How do I fix this? Is it a speaker problem? Is it an internal/DSP problem? How do I go about repairing something like this? Does it need to be taken apart? Do I need a new component? Any help would be appreciated. Thanks

FM or NFM?

HudsonScannerGuy · May 5, 2018

Both. AM seems to work just fine though, Could it be something internal? Ie a cap or resistor blown?

HudsonScannerGuy · May 5, 2018

I have verified FM and NFM doesn't work. I have verified P25 reception is okay, a little shaky at best, but it works loud and clear. It's just FM and NFM that are VERY quiet. Even with headphones on.

iMONITOR · May 5, 2018

just on one freq? Maybe it's low modulation on their transmitter? Does that scanner have audio +/- level settings for each freq?

HudsonScannerGuy · May 5, 2018

It's on any FM/NFM frequency I program in.

iMONITOR · May 5, 2018

Firmware updated?

HudsonScannerGuy · May 5, 2018

Havent checked.. and I dont have a programming cable

HudsonScannerGuy · May 5, 2018

Checked versions
uP app: RF2.6
DSP VER: 1.4
DSP Voc App: 1.0

scanmanmi · May 5, 2018

Did you do a factory reset?

HudsonScannerGuy · May 5, 2018

Yes. I'm thinking it's an internal/modulation issue.

HudsonScannerGuy · May 5, 2018

Should I try resetting the DSP?

ecps92 · May 6, 2018

I assume this is on a local PD/FD Channel ?
How is the audio from the NWS ?

IF NWS is fine, then the issue is with the actual agency, not your radio

HudsonScannerGuy said:
I recently acquired a PRO-651 from a local in town and I discovered it had low audio on FM, but AM modulation seems fine. How do I fix this? Is it a speaker problem? Is it an internal/DSP problem? How do I go about repairing something like this? Does it need to be taken apart? Do I need a new component? Any help would be appreciated. Thanks

HudsonScannerGuy · May 6, 2018

No it's *every* single channel thats either NFM/FM. P25 decodes alright, and AM sounds okay. It's probably something internal to the radio.

ecps92 · May 6, 2018

Do me a favor and re-Confirm the Weather is also low audio

HudsonScannerGuy said:
No it's *every* single channel thats either NFM/FM. P25 decodes alright, and AM sounds okay. It's probably something internal to the radio.

HudsonScannerGuy · May 6, 2018

I can confirm that every FM/NFM frequency and TSYS is low audio. AM stations such as CB and aircraft come in LOUD and clear. NWS is also low but recieveable. All signals recieve as if the unit was new, just the audio is low. I did full reset, reset DSP, and tried messing with attenuation. I did open it up briefly to take a look inside and I smelled the very recognizeable burnt smell of electronics.. that might be a clue..

RFI-EMI-GUY · May 6, 2018

It could be wildly off frequency, though P25 should suffer range problems (volume would be OK though).

RFI-EMI-GUY · May 6, 2018

oh the sniff test. Well, probably got hit with a voltage spike.

HudsonScannerGuy said:
I can confirm that every FM/NFM frequency and TSYS is low audio. AM stations such as CB and aircraft come in LOUD and clear. NWS is also low but recieveable. All signals recieve as if the unit was new, just the audio is low. I did full reset, reset DSP, and tried messing with attenuation. I did open it up briefly to take a look inside and I smelled the very recognizeable burnt smell of electronics.. that might be a clue..

HudsonScannerGuy · May 6, 2018

How do i tell what components got hit in the spike if it got hit with one?

RFI-EMI-GUY · May 6, 2018

I would "nose" around and look at the voltage regulators for obvious damage and even check voltages. This assumes you can find a schematic. Then there is probably a CMOS transmission switch to route the audio between the AM/FM/Digital modes. That could be damaged or the driver damaged. If something smoked, you should be able to find a discolored component.

Pro-651: Low audio on FM modulation.

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