galaxy dx88hl lost recieve

[jef]

Had a real strong close station come in to my receive and took it out,the radio still shows receive on meter and can hear very weak static through speaker with volume all the way up.PA mode is not working either but have great modulation on am and sideband .Could it be the audio ic even though I have transmit? I tried an external speaker also and same results.This radio had a very nice receive before this.

 

[Robb]

Transmit audio is going thru IC4/njm4558.

To test audio output, turn up the vol 1/2 way, and then touch each pin on the trace side of the board of the audio chip and then listen for a loud hum in the speaker. Don't recall which pin it is ATM. If you hear it; then the audio IC is probably OK. If you don't; then it is either the audio chip is bad or one of the four electrolytic caps in that circuit has gone fault.

http://www.cbtricks.com/radios/galaxy/dx88hl/graphics/sch_dx88hl.pdf

 

[jef]

Transmit audio is going thru IC4/njm4558.

To test audio output, turn up the vol 1/2 way, and then touch each pin on the trace side of the board of the audio chip and then listen for a loud hum in the speaker. Don't recall which pin it is ATM. If you hear it; then the audio IC is probably OK. If you don't; then it is either the audio chip is bad or one of the four electrolytic caps in that circuit has gone fault.

http://www.cbtricks.com/radios/galaxy/dx88hl/graphics/sch_dx88hl.pdf

Have a hum from speaker when I touch pin 4 of audio chip, pa jack in back of radio checks fine the meter is showing receive and there is slight noise out of speaker.Audio chip voltages all check spot on,which caps should I be looking at?

 

[nomadradio]

How strong is "REAL" strong?

Did a truck driver pull alongside with his antenna a foot from yours and key his BandSmasher 5000?

That would be "real" strong. Maybe strong enough to damage components inside the radio.

Or do you mean "real" strong, as in a skip signal from 2000 miles away? Not the same thing.

I'm not convinced that the radio's problem is related to anyone's 'strong' signal if it came from more than a few feet away.

A radio that's probably 25 or more years old can randomly break down at any time, no matter how strong someone's signal was.

73

 

[jef]

How strong is "REAL" strong?

Did a truck driver pull alongside with his antenna a foot from yours and key his BandSmasher 5000?

That would be "real" strong. Maybe strong enough to damage components inside the radio.

Or do you mean "real" strong, as in a skip signal from 2000 miles away? Not the same thing.

I'm not convinced that the radio's problem is related to anyone's 'strong' signal if it came from more than a few feet away.

A radio that's probably 25 or more years old can randomly break down at any time, no matter how strong someone's signal was.

73

Okay I had my sencore cb42 and was going to set meters had the sencore microvolt set for x10, (should have been on x100) and turned up to 5 on the other knob that's what caused the strong signal also had volume turned just under half,took receive out. Ic4 voltages on transmit and receive checked good also.

How strong is "REAL" strong?

Did a truck driver pull alongside with his antenna a foot from yours and key his BandSmasher 5000?

That would be "real" strong. Maybe strong enough to damage components inside the radio.

Or do you mean "real" strong, as in a skip signal from 2000 miles away? Not the same thing.

I'm not convinced that the radio's problem is related to anyone's 'strong' signal if it came from more than a few feet away.

A radio that's probably 25 or more years old can randomly break down at any time, no matter how strong someone's signal was.

73

 

[Robb]

Have a hum from speaker when I touch pin 4 of audio chip, pa jack in back of radio checks fine the meter is showing receive and there is slight noise out of speaker.Audio chip voltages all check spot on,which caps should I be looking at?

These are where to test first; but not exclusively the problem spot. But if you test them and any of them fail; then there is a pretty fair chance that there are other caps in the radio that have failed. Radio is ~25 years old; time to expect this situation. JMHO.

Example: Was working an audio problem in a radio this week, the speaker was getting so hot I could have prepared a grilled cheese sandwich on it. But audio was still coming out. Main audio cap had gone completely short. Old radios are like a box of chocolates; you just never know what you are going to get - lol . . .

Please read this:

The 10-Volt Blues.

This refers to a pattern of failures found in solid-state CB radios that get to be 20 or more years old.

These radios are packed with dozens of small aluminum-electrolytic capacitors. This type part is irresistible to the product's designer. Does a really good job in a small package, and at low cost. Just one drawback. They get old and fail.

Twenty or more years down the road. Joe design engineer doesn't care about that.

The most-evident pattern that emerges after repairing the first few hundred of these failures is that the caps with the lowest voltage rating tend to fail first. Must have something to do with the chemistry inside these parts, but that's not my department.

What we learned to do was replace the whole "family" of 6- and 10-Volt rated caps any time the first one of them goes bad in that radio. And you'll find production changes. A Cobra 142 made in one year might have a 10-Volt cap in a spot where you see a 16-Volt part in radios made 5 years later.

One cap that goes bad will kill the receiver's audio only. The S-meter still kicks around on channel noise, and transmit side is not affected at all.

Another one causes the AM transmit audio to squeal when the carrier power is turned down.

Yet another will kill all your transmit, AM and SSB both, but leave the receiver unaffected.

Probably the worst one of the bunch will cut the transmit power in half or less. The only immediate clue will be that the final's bias current remains zero no matter the bias-trimpot settting.

The life of these parts may extend to 40 years or more. And that 20-year mark is not a minimum, by any means. The operating temperature of these parts will have an influence. Mileage is a big deal, but there is no odometer on a radio to see how many thousand hours of heat stress have been put onto the parts inside.
A 20 year-old radio that's new in the box probaby won't have any failed caps. And a radio that was turned on and run 24/7 for 15 years is a lot likelier to exhibit the 10-Volt Blues.

One odd pattern that emerged was the "spare radio on the shelf" failure. Typical example was a Uniden-made 40-channel SSB CB like a Madison or Washington that was used for 15 or 20 years. When it got replaced by a bigger "black" radio like a Galaxy or RCI, this one goes on the shelf as the spare base station.
And there it sits for 3, 4 or maybe 5 years until the big radio takes a dump and goes out for repairs. The spare radio comes off the shelf and gets powered up for the first time in several years.

It lasts for a week or less, and one of the symptoms above appears.

And that's the pattern. A well-used radio lasts only a week or less after a long shelf visit and then quits.

My favorite of all the 10-Volt Blues failures is the cap that burns out the coil in your speaker and the audio chip both when it fails as a short circuit.

The cool part is when someone leaves that shorted cap in the radio and replaces the audio chip and speaker. The chemistry in the failed cap sometimes causes the short to go away. But only for a while. Even if the person doing the repair were to "test" this cap it would show okay.

Until it shorts again and blows out the speaker and audio chip.

Again.

That part is one we learned to just change in any radio over 25 years old, whether it checks bad or not.
Cheap insurance.

73

 

[nomadradio]

Try the 'finger on a screwdriver shaft' trick on TR42. Can't remember which of the two outer leads is the base, but the hum should be a LOT louder on that one.

I call that tool the "Manual Digital Signal Injector".

And if you get only a weak hum from the center leg, check C156 to see if it has shorted.

And if this isn't where the trouble is located, next place to check is the squelch transistor. Unsolder the center leg of TR16 so that it doesn't touch the rim of the hole in the foil pad. If this brings back the receiver audio, there is a problem in the squelch circuit.

73

 

[jef]

Thank you guys ,Robb was right it was c145 changed it out from a shot 330uf 16volt to a 35 volt 330uf and learned a big lesson to check my settings on my cb42 before turning on.Thank you very much for helping me solve this.I am going to change out the rest of the caps in that section now.Again THANK YOU! typo repaired

 

[Robb]

Thank you guys ,Robb was right it was c145 changed it out from a shot 33uf 16volt to a 35 volt 33uf and learned a big lesson to check my settings on my cb42 before turning on.Thank you very much for helping me solve this.I am going to change out the rest of the caps in that section now.Again THANK YOU!

...change them all and be done with it - JMHO . . .

EDIT:
C145 is supposed to be a 330uf - BTW . . .

 

[jef]

...change them all and be done with it - JMHO . . .

EDIT:
C145 is supposed to be a 330uf - BTW . . .

My typo, I did put a 330uf in c145 and she works great problem solved thanks again.

 

[nomadradio]

Rock on!

Gotta love it when a plan comes together.

Congratulations and 73