Spectra audio problem help

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kf4sqb
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Spectra audio problem help

Post by kf4sqb »

I have an A4 dash mount Spectra, model # D43KMA7JA4AK, with an audio problem. I get absolutely no speaker audio, except for a "pop" when audio "starts". For instance, when pushing a button like scan, that normally "beeps" when pressed, I get nothing but a pop from the speaker. I've checked the board for signs of capacitor leakage, and everything looks very clean, even under a magnifying glass. Does anyone have a schematic of the audio circuit they can send me, or some tips on what exactly to check to determine what exactly is wrong? Even a simple pinout of the audio amp IC would be helpful. Thanks!
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MT2000 man
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Re: Spectra audio problem help

Post by MT2000 man »

I know you said you already checked for leaky capacitors, but what you describe ( especially the "pop" sound ) is a prime example of what happens when a capacitor craps the bed. Mine did the same thing, ( only I HAD audio, but VERY low, and I also had the pop sound as well ). Sent it out to a very well respected battlaber, had ALL capacitors replaced and she works like new now !
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kf4sqb
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Re: Spectra audio problem help

Post by kf4sqb »

Yeah, I understand that it could still be a bad cap, but would like some more detailed service info to be able to tell for sure before I attempt working on those tiny surface mount parts.
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PETNRDX
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Re: Spectra audio problem help

Post by PETNRDX »

I second the motion to change the caps.
I also have had some that looked, and smelled good inside, but had bad caps and no audio except the pop on power up or button push. Some damage under the cap.
Get some Tantalum or electrolytic caps and change them out.
Once you get into the work, it is not that bad.
Then again, if you don't do any small solder work, there are plenty of folks around that can do them.
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Bill_G
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Re: Spectra audio problem help

Post by Bill_G »

A KMA version Spectra is old enough to be suspect of bad caps. If you don't have a service manual, you should get one. You want the command board section for the audio amp. Use an LED flashlight to check the solder around the caps. If you get a blinding reflection, the cap has not leaked YET. If it is dull, it's time to swap it out. Look for subtle dark discolorations in the solder resist on the board. The oil leaks out and creeps under the solder resist making it much darker. Check the command, rf, rfpa, and control head boards. If you find one leaking anywhere, replace all the electrolytics in the radio. It could be the audio amp itself has died, and needs replacement. If the command board caps have leaked badly enough, you may need to also replace the two tantalum caps and blister resistors on the audio output. The rf board caps have a habit of destroying a resistor in the vco line. You will also need to check / repair the feed through eyelets in that area as they are often destroyed. Depending on the extent of the damage, most boards can be recovered. Occasionally one is beyond repair.
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kf4sqb
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Re: Spectra audio problem help

Post by kf4sqb »

I've checked all the caps in the radio, and they all have clean, bright, shiny solder joints, and no discoloration of the solder resist. I understand that they can still be bad with no leakage, but knowing the guy that I got this from, he may well have done something just slightly unintelligent, like cutting the speaker wires with the radio still powered up while removing it. He replaced it for the upcoming corparately-backed FCC screwing-over, and gave it to me, basically for free. I'm just planning on using it for a 2m Ham base install. I'll try replacing the caps and see what happens.
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Re: Spectra audio problem help

Post by Bill_G »

No. Get in there with a scope probe or inductive coupler to listen to the audio pa. If you locate the two orange tant caps next to the large 10uf electrolytic, you can listen there. Open the squelch and listen for noise. Chances are the pa module is bad.
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kf4sqb
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Re: Spectra audio problem help

Post by kf4sqb »

Bill_G wrote:No. Get in there with a scope probe or inductive coupler to listen to the audio pa. If you locate the two orange tant caps next to the large 10uf electrolytic, you can listen there. Open the squelch and listen for noise. Chances are the pa module is bad.

How about a little more detailed info, Bill? There are no orange caps near the large 10uf electrolytic. Mine has the large 10uf @ 50v, three 10uf @ 16v electrolytics (look just like the large 10uf, only smaller), and several chip caps near the audio PA. If it helps, the command board is model HLN6094, rev. C.
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Bill_G
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Re: Spectra audio problem help

Post by Bill_G »

Over by the largest 10uf and next to the MLM frame should be two rectangular plastic caps. Usually yellow or orange. You can look at the audio output at the points towards the 10uf.
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Re: Spectra audio problem help

Post by WB6NVH »

Remember that the Spectra audio output must float.

The only way to check the caps is with an ESR meter. Just because they haven't leaked doesn't mean they are any good. I have seen many that didn't leak but they were open.
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kf4sqb
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Re: Spectra audio problem help

Post by kf4sqb »

After finally getting some service info (Thanks, Jim), I've checked a little more on this issue. There is audio coming into the audio IC, but nothing coming out. Caps all look good, but I replaced them anyway. Still no output. Changed the audio IC. Still no output. Now what?
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maxkelley_kc2spy
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Re: Spectra audio problem help

Post by maxkelley_kc2spy »

kf4sqb wrote:After finally getting some service info (Thanks, Jim), I've checked a little more on this issue. There is audio coming into the audio IC, but nothing coming out. Caps all look good, but I replaced them anyway. Still no output. Changed the audio IC. Still no output. Now what?
Change the radio. :lol:

But in all seriousness... I hate Spectras. Even when their caps are OK, their audio is, sure, loud, but horrid quality. Anywho, I digress. It's time for caps!! They're super-cheap, just require a little bit of labor to get them in. Even so, it's often the case that the caps have already done their damage.
Max Kelley KC2SPY
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MT2000 VHF & UHF A7, Visar UHF, ASII UHF, Maratrac UHF, Astro Spectra UHF, MCS2KIII 900, XTS2.5K-Q
MT2000 man
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Re: Spectra audio problem help

Post by MT2000 man »

I think you're the first person on this forum that hates Spectra's ( I'm sure there's others, but they are all hiding lol ).
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kf4sqb
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Re: Spectra audio problem help

Post by kf4sqb »

I've already replaced the caps. Absolutely no sign of any leakage underneath.
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Jim202
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Re: Spectra audio problem help

Post by Jim202 »

Time to pull out the Ohm meter. Start with measuring the speaker and see if you have resistance across the wires after disconnecting it from the radio. If yes, then you need to do the same with the control cable all the way back to the command board.

If the cable checks out resistance wise on both wires all the way to the control board, your left with an issue on the control board. Back to using the scope. Trace both paths from the audio chip through the capacitors to the control board connections leaving the board. My guess is that you have an issue on the control board.

Jim
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kf4sqb
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Re: Spectra audio problem help

Post by kf4sqb »

Jim, I'm looking at the audio on pins 11 and 13 of the audio IC with a signal tracer by hooking the tracer on both pins, not by hooking to one pin and chassis ground. Its dead there. Audio coming into the IC, just a pop leaving it. Think maybe I need to look at the control side of the IC and see what things look like there?
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