Spectra Audio Popping AFTER capacitor replacement

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Spectra Audio Popping AFTER capacitor replacement

Postby Tim » Tue Nov 24, 2009 8:37 pm

Hi Folks,

Anybody have any ideas about audio pops on a spectra after the
caps have been replaced? It happens when the amp is enabled
(unsquelch the radio, beeps/mode changes, etc). (VHF Front
mount Spectra).

Although not totally obnoxious, I would like to reduce the amplitude.

Just curious before I get the scope out & start looking.

Thanks!

Tim
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Re: Spectra Audio Popping AFTER capacitor replacement

Postby Bill_G » Tue Nov 24, 2009 8:47 pm

Check the tantalum bypass caps and resistors for corrosion and/or open traces especially if the large 10uf cap was leaking badly. Did you lift the command board out and inspect the bottom side? That stuff wicks down the feed through holes and raises heck down there too including on the audio output lines.
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Re: Spectra Audio Popping AFTER capacitor replacement

Postby Tim » Wed Nov 25, 2009 6:56 am

Hi Bill,

Thanks for that. I'll check under the tantalums. I did pull the
board out, & it looks real clean underneath. Can't see any
corrosion on any of the vias. Did find some additional
ant i bodies!

Thanks,

Tim
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Re: Spectra Audio Popping AFTER capacitor replacement

Postby wa6ylb » Wed Nov 25, 2009 8:18 am

We have seen the audio chip itself have issues. Look at the legs on the audio chip. If they are not all silver color, but rather a dull brownish yellow color, then look into replacing the audio chip. I have also seen
what looks like something oozing and sizzling out of the legs of the audio IC itself.
In any case, replacement of the audio chip, and or caps around it usually gets rid of the popping sound.
B.
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Re: Spectra Audio Popping AFTER capacitor replacement

Postby linkinpark9812 » Wed Nov 25, 2009 2:31 pm

Well, I think you have the same problem I had. I can almost bet you it was one of your capacitors that you replace by the audio chip. I am not the best at soldering, so I probably shouldn't have done the "repair" myself. Since near the Audio IC was the hardest to replace (4 capacitors in a tight space), i managed to burn at solder pad. It had lifted off of the board enough, but I didn't notice it. It took me a few weeks to notice, because every time the audio UNMUTED, I would get a pop that I swear I did not hear before.

I looked into the audio IC and how it uses capacitors to prevent popping on mute/unmute. Using a multimeter, i found out it was one of those capacitors (don't remember which one, I know it was one of the two that are right next to the Audio IC pins.

So I removed one of it's legs, and it really only went a short distance to an audio IC pin. So I just moved the leg, soldered on the leg to the Audio IC Pin leg, and BINGO, no more popping.

If you didn't have the audio pops before the replacement, but have them now, I would put my money on that being the problem. Check those 4 capacitors near the Audio IC, test each pad (put one end on the solder pad for the capacitor and the other on where the trace on the board goes to from that pad, which is usually an Audio IC pin). Maybe your problem isn't as bad as mine. Maybe you just have a bad solder job on one of the capacitors rather than a burned off solder pad.

Good Luck! Happy Thanksgiving in advance! 8)
Radios I own: Spectra VHF 110W with A7 head, HT1000 VHF, ICOM IC-F30 VHF, and a Puxing PX-888 VHF.
Scanner I own: Radioshack Pro-164

If you want to get around the 16 mode scan limit on the Motorola Spectra, then read this guide and go to the original thread Here! 8)
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Re: Spectra Audio Popping AFTER capacitor replacement

Postby WB6NVH » Mon Nov 30, 2009 4:53 pm

Other than Moto, has anyone found a reasonable source for those audio IC's? They seem to be something you don't find at Mouser or Digi Key.

By the way, an ESR meter is really useful to test all the caps. If any of the tantalums are open, you can see that easily. I found it pointless to measure the factory electrolytics as 90% of them seem to test open (bad) and it would be pointless to leave any in there.
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Re: Spectra Audio Popping AFTER capacitor replacement

Postby Will » Tue Dec 01, 2009 2:36 am

WB6NVH wrote:Other than Moto, has anyone found a reasonable source for those audio IC's? They seem to be something you don't find at Mouser or Digi Key.


We have replacement audio output ICs available. No they were mfg'd only for Motorola. You can use another IC in there but the pinouts are different.
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