CDM 1550 No Audio (well, kinda...)

[jorenwendschuh]

I'm not sure what the initial use for the radio was, but it looks like it was used as some kind of a data radio - the speaker leads were clipped within the head - so obviously there was no audio out.
Removed & Replaced the head - neither the internal speaker nor an external speaker volume change with the control knob - it is super quiet - but still audible if you get right up to the speaker - clear too, unless you press a few buttons too quick - then it barfs out a louder tone that is more normal volume, but quite distorted.

Are there any soft settings for the volume control / audio output?
It seems to be either at the opamp driving the audio amp, or before the mixer IC - as the recieved audio level entering the mixer IC looks GREAT on a scope - maybe +/- 1vPtoP, but passed that I can barely see the movement on my scope.

Any other ideas on what it may be?

CDM 1550 VHF without passport board - sitting on the bench.

Thanks.

[Will]

Radio may have been programmed for Handset, which disables the audio output stage.
The volume control may have been disabled, cut Vol Hi wire.

Seen lots of Hack jobs, some even from the 'factory'.

[jorenwendschuh]

The only control I can find for the handset audio is under Radio Configuration - Accessory Configuration - Checkbox for Handset. Checking this box makes every tone but the normal startup beeps muted from the speaker - but the startup tone is still there. Removing the Check returns the unit to the current state where all audio and tones are quite low in volume - there but just very very quiet.

Volume control is only analog in the control head by my understanding - it goes back to the radio itself within the digital control scheme - where would the vol hi wire be cut that is not in the control head?
-I've replaced the head with a known working good one - twice now - no change.

Any other ideas? Are there any software volume controls somewhere in the tuning or codeplug? (There is for the HT I believe - can't find them for the CDM though - could be I'm just blind...)

Thanks!

[jorenwendschuh]

Another piece to the puzzle - the Rated Volume Tuning (Carrier Squelch environment) control in the tuner allows the volume to increase - its default was ~180 - putting it to 255 makes the speaker much louder - but for sure not the normal 'high volume' of all other CDM's I've worked on. Strange!

[jorenwendschuh]

One more tidbit - Once turning up the CSQ volume - I was able to hear that there is a difference in audio levels when running the volume knob on the control head up and down - it is like the control head is telling the uP the right things - and the uP just has a very very low multiplier inline with the audio line - something is holding it back.

[jorenwendschuh]

Anyone? I can't locate any board modifications or anything that looks out of place. My next step is to try and just update the firmware - see if that changes anything. It is a 5.xx firmware version, just not the newest.
Is there anywhere I can probe to see if it's a software issue, or a hardware issue?

[AEC]

If the config setting are 'maxed', and external mic inputs are not used, then the last resort is a blown voice coil on the speaker.
CDM panels are assembled like Mattel toys, snap-together, and the speakers rattle when you remove the faceplate, as does the display separate from the board, but you may want to try a different speaker, just to test the possibility of it actually being bad.
Also, look at the rear accy. plug, is there a black wire looped to disable the horn/emergency option?
If it is bare, put an acc. plug on that has that wire.

[jorenwendschuh]

Tried updating firmware - goes into bootstrap mode and then the updater says it's not in bootstrap mode and kicks out. Was hoping for an easy fix.


The front panel has been replaced thrice now, and an external speaker was also hooked up - it's not a problem in the control head, as these devices all work before and after on other known working radios. Flashing worked on those radios as well, so its this radio that's giving me the trouble.

The horn / emergency option is not enabled in the CPS.

What configuration settings besides the ones specified above are available on the CDM series? I can't say for sure that they are all 'maxed' as I have gone through but may have missed something.