Motorola CM300 Audio PA

[JD]

I have a CM300 that is only indicating about 50% of rated audio output. No external speakers, customer did have pins 15 and 16 jumpered, why ???? Is this a PA issue and can these be replaced or have to be sent to ElpasoMexico ?
Thanks.

[Al]

Can you tell us how you're measuring the audio output power? The CM series has a single IC that's in a BTL configuration, so within the design limits of the IC, the output power that you'll measure across a specific value of load resistance is inversely proportional to the load's value.

[JD]

Across the speaker leads , using vom . Sound volume is what made us notice, about half of another CM300.

[Al]

The CM300 rated power is 7.5 watts into a 4 ohm load. It's pretty hard to tell whether you've got a bad audio output IC or a bad speaker checking it the way you've done. Audio output ICs have been toasted in these radios when the user grounded one side of the speaker wiring. If you disconnect all speakers, you should see about 6.5 to 7.0 volts DC from each speaker lead to ground if the audio IC is OK - that would be from accy connector pins 1 and 16 to chassis ground. If this checks OK, then you might look at the external speaker for a shorted voice coil, and check on another known good radio.

[JD]

Thanks for the assitance. I will try that. The audi volume is low on both internal speaker and, external speaker. The internal speaker is disconnected when the external is used.