Strange PA Happenings

[fchrist16]

Okay guys here's a brain-teaser for you.

Motorola Spectra VHF with a HLN1185 Siren Box. Everything was working PERFECTLY until recently. Now I get a muffled/scratchy sound. When I bring up the PA, the audio is just completely gone by the scratching noise. When using the optional Audio-Routing, when I put the PA Speaker over Volume 10 the muffling and scratchy audio kicks in. When working in the area I do, anything below a level 12 volume won't do due to ear protection and the loud noise I'm constantly around.

Any ideas as to what's wrong? I haven't torn all the wiring apart yet but that is my next step. This radio has had a full re-cap and tune up by Will a few years ago. The speaker is an unknown 100w speaker bought at a ham swap a few years ago and is in perfect operating condition.

EDIT: I do notice that using the mic I have for that radio (an ex-Washington State Patrol mic) has been fine with audio reports, etc., but my other mic (non-rocker) could be substituted in if needed.

Regards,

-Frank C.

[jmfirefighter20]

If you have another speaker I would try swapping it out first. If it still occurs then you know it's the wiring or box.....good ol' process of elimination.

[Jim202]

Okay guys here's a brain-teaser for you.

Motorola Spectra VHF with a HLN1185 Siren Box. Everything was working PERFECTLY until recently. Now I get a muffled/scratchy sound. When I bring up the PA, the audio is just completely gone by the scratching noise. When using the optional Audio-Routing, when I put the PA Speaker over Volume 10 the muffling and scratchy audio kicks in. When working in the area I do, anything below a level 12 volume won't do due to ear protection and the loud noise I'm constantly around.

Any ideas as to what's wrong? I haven't torn all the wiring apart yet but that is my next step. This radio has had a full re-cap and tune up by Will a few years ago. The speaker is an unknown 100w speaker bought at a ham swap a few years ago and is in perfect operating condition.

EDIT: I do notice that using the mic I have for that radio (an ex-Washington State Patrol mic) has been fine with audio reports, etc., but my other mic (non-rocker) could be substituted in if needed.

Regards,

-Frank C.

There is a good possibility that your seeing the leaky cap problem in the Spectra. They are prone to the surface mount caps that start to go bad and leak their electrolytic goop. Allowed to go on long enough and the traces on the board will be etched away. Sometimes it is just the caps loosing their value and no longer function. Generally you start to hear pops in the audio first. Then the audio starts to have this sort of frying static with it. Then you can't understand what is being said.

There are all sorts of threads on this subject. Most of them have photos to show you where to look. Do a search and then sit down and read.

Jim

[jackhackett]

Jim, you must have missed where he said Will recapped his Spectra.

Now to be clear, Frank, you're talking about the audio coming out of the siren PA?

If so, isolate the problem to either the radio or siren. If the radio speaker audio is fine at all volume levels and the transmit audio is fine, the siren box or speaker would most likely be the problem. Bad siren speakers can sound okay at low volume but distorted at higher volume. Also I would imagine if the siren is the same vintage as the radio it could have capacitors going bad as well.
Another possibility would be the siren not getting enough power, check that it's getting good voltage and current. And check that the cable connections are clean and seated well.

Good luck with it.

[fchrist16]

I have another speaker I can test at home (400+ miles away).

Yes I am talking about the audio coming out of the Siren PA. Worked fine until about 3 months ago.

Jim you must have missed it that Will recapped the radio a few years ago.

Regards,

-Frank C.

[d119]

Is it possible the siren box is susceptible to the same capacitor issue?

[wx4cbh]

Speaker diaphragm cones go bad from time to time, especially with age and/or some type of physical damage from water intrusion, etc., and this sounds typical of bad cone syndrome. If you don't have a substitute speaker assembly and can obtain a replacement cone for that specific model, that would be where I would start. It's a relatively easy procedure to accomplish and way less expensive than a new speaker assembly.

[fchrist16]

Speaker diaphragm cones go bad from time to time, especially with age and/or some type of physical damage from water intrusion, etc., and this sounds typical of bad cone syndrome. If you don't have a substitute speaker assembly and can obtain a replacement cone for that specific model, that would be where I would start. It's a relatively easy procedure to accomplish and way less expensive than a new speaker assembly.

I'll check the PA speaker out but it's in a well shielded (from rain/elements) area so I'm not sure. I'll give it a check.

Regards,

-Frank C.

[fchrist16]

So now I'm seeing SPKR SHORT on the radio when I bump the PA volume above 9 or 10. The volume starts to drop off through the PA after volume 12/13.

Any ideas? Time to swap out the HLN1185??

Regards,

-Frank C.

[Bill_G]

Is it possible the siren box is susceptible to the same capacitor issue?

Yep. All Moto product that used those surface mount caps were subject to them leaking after about a decade.

[fchrist16]

Alright, time to swap out boxes! Thanks Bill.

Regards,

-Frank C.