Galaxy saturn

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supremme
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Galaxy saturn

Post by supremme »

Hello, I have a galaxy saturn with a somewhat strange problem, I have no modulation in am/fm and there is no power in ssb, if I inject a 1000hz signal with the service monitor on pin 3 of ic4, I have the tone in am/ fm and the power in ssb, I have checked the 754 transistor, its 473 driver and its predriver, I even changed the 754 for a tip 147 without success, I also replaced IC4 with a new one, putting a socket on it, tr32 seems to be fine, I also changed the AN612 balanced modulator without success, there is something that I am missing and I don't know what it could be.
lbcomms
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Re: Galaxy saturn

Post by lbcomms »

Could be any component from the mic socket up to the modulator circuitry, including the mic gain pot (if that radio has one), or could be the circuit boards themselves such as a cracked solder joint or an open circuit trace. Easily traced with an oscilloscope, follow the path until the audio disappears. Without one, you are changing parts at random and hoping for the best. Good example of having the right tool for the job in this case.
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dt307
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Re: Galaxy saturn

Post by dt307 »

sue is on the money ....but being a kitchen tec with little to no test gear for a long time there is a way around it.
you are able to inject onto ic4 so inject from the start of the audio path ie the mic then mic socket all the way un till you get to ic4.
if you think logically ... no fm and am audio no power in ssb yet injecting into ic4 you get a tone in am and fm and ssb power = the problem is before ic4 and the starting point ie the mic... because you have a common problem in all modes.
changing the 754 ect is like going for a haircut and taking your shoes off lol...just no point.

check the mic is good dont assume
lock the radio in tx and on ssb and monitor you output power (if you dont know how to lock the radio into tx for testing ..send it some one else )
inject into ic4 to see everything is all setup correctly ie your injection and power meter ect (make sure probe is decoupled against dc)
while locked in tx start at the mic socket audio pin inject into that bad boy and follow the schematic diagram audio path one stage at a time ie socket/mic gain pot/series caps ect ect
good luck

and yes with the right tools this is a 5 min issue to pinpoint
163dt307-chris




“I fear the day that technology will surpass our human interaction. The world will have a generation of idiots.”
― Albert Einstein
supremme
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Re: Galaxy saturn

Post by supremme »

Thanks for all the answers, I have technical instruments, a service monitor, digital oscilloscope, tester, etc. One thing I forgot to mention is that in public address the device modulates perfectly, the echo works also, when connecting the low frequency generator to the connector microphone, the 1khz 10mv signal drops a lot, change several electrolytic capacitors that usually fail in these devices without success.
Nodens
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Re: Galaxy saturn

Post by Nodens »

Supreme,can you desolder the TR32 collector temporarily to see if the ssb modulation and power returns?
supremme
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Re: Galaxy saturn

Post by supremme »

Yes, I did that test without success, there is no power in ssb or modulation in am/fm
Nodens
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Re: Galaxy saturn

Post by Nodens »

then inject an audio signal at microphone socket and trace it with oscilloscope the path to ic4 to see where is being dropped it, inject enought signal level for the oscilloscope being able to see it.
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