I have a galaxy dx-44 on the bench here. When i got it it had to tx or rx and i found that tr43 and tr44 were both shorted. I replaced them and tr36 wich was shorted out. I have tx back now and working perfectly. Now on the rx side i found that someone put a 1n4148 in place of a 7.5volt zener at d78. I replaced that and still no audio. I have no talkback and no pa. I found that on tr36 i have no 8.5 volts to turn on rx. I pulled tr36 and 37 and checked them on my b&k tester and they are fine even the leakage is fine. So i tried injecting signal into the audio chip and i just hear a low signal if i put my ear up to the speaker. So i replaced the audio chip and still no ops. I also check the speaker jack in the back it is fine also. i replaced c145, C146, C150, AND C151. Still no audio. fixed a couple of solder joints. Still no ops. starting to see a pattern here yet ha ha ....... oh well lets continue anyway. I check tr42 and it is ok also. tried injecting a audio signal agian no luck with that eather. I will list some voltages that i have on my NEW adio chip so far. I will also list some other ic's and transistor voltages. keep in mind i have no rx but tx does work.
I have the service manual here for the EPT3600 chassis, so I have checked your voltages against it.
IC8 (Audio amp) - OK
IC4, pin 6 voltages look wrong, it should be 7.8V in TX (probably in RX too), all other pin voltages are OK.
TR36 (RX switch) is not correct, should be B-7.8, C-8.5 (RX) or 0 (TX), E-8.5V
TR37 (RX switch) is not correct, should be B-0 (TX) or 0.7 (RX), C-0(RX) or 8 (TX), E-0.
(Are you sure you didn't label them back to front?)
I think you need to also check the voltages for TR38 (RX switch), they should be: B-8.03 (RX) or 7.7 (TX), C-0(RX) or 8 (TX), E-8.5.
So based on this information I suspect that either IC4 may be blown, or there could be a problem with R166, which passes the pin 8 voltage to pin 6 (pull up), R169 is a pull down so if there were no signal from the PLL pin 6 should be at about the voltage you state, the lock detector output from the PLL should pull pin 6 high, D66 passes the lock detector signal from the PLL to shut off TX if the PLL is not locked (check D66 too) (7.5V locked, 0V unlocked).
I believe the PLL simply pulls that pin to 0V when unlocked, and because the voltage on pin 6 of IC4 is close in the middle of its supply voltage, it could be causing the device to turn on/off with any slight voltage change (in TX the 8V supply could drop a little, meaning that the 3.3V on pin 6 turns into a high signal, but in RX the 8V supply could be a little higher, meaning that the 3.3V would be a low signal, as a high or low signal is relative to the devices DC supply voltage.
Last edited by The Defpom on Friday 6th Jun 2008, 10:18, edited 2 times in total.
With D78 being replaced by a 4148, I suspect that everything on the constant 8VDC rail got 13V through it, so any faults could be in other parts of the radio, for instance, this would have put 13V onto the PLL (not good), some devices are rated for that kind of voltage and would be uneffected, other devices may only be rated for 8 or 9V max, in which case they could have been damaged, just something to bear in mind.
ok thanks I replaced Ic4 and it didnt make any difference so i think it is ok. I will check some of the other things mentioned thanks for the quick response.
OK THANKS RICK I MISSED THAT DIODE. It is hiding down in there pretty good. I checked it and as you know it was a 4148 instead of a zener diode. replaced it and now the rx light lights up and the meter just slams. transmit still works though. I still have no audio and that one has me puzzled because i put a new ic in after i fixed the voltage regulator problem. and replaced all the caps mentioned that could have been short. you know how you touch the audio ic and you get some noise well i dont even get that at least not loud anyway just real faint. let me know what you think about that one. I am going to replace the pll too just to take that out of the equation.
Check the squelch is working, Pins 8,9 and 10 of IC1 and TR16.
IC1 maybe have failed.
Try lifting on end of D80 to see if the RX audio returns.
Check TR42
Try a PA test.
I lifted D80 and still no audio. I also tried a pa test and no audio there either. i checked tr42 and it was ok also. I am going to do some more digging.
I found the voltages on ic1 were all over the place so i pulled it. I found that the meter doesnt slam in rx mode now so i assume that this was another part of the problem.
As for the audio lift one let of C155 and try to inject a 1 KHz signal in to the junction of R207 and C154 you should be able to ear this, if not the fault is around the audio IC.
speedracer6g wrote:I have a galaxy dx-44 on the bench here. When i got it it had to tx or rx and i found that tr43 and tr44 were both shorted. I replaced them and tr36 wich was shorted out. I have tx back now and working perfectly. Now on the rx side i found that someone put a 1n4148 in place of a 7.5volt zener at d78. I replaced that and still no audio. I have no talkback and no pa. I found that on tr36 i have no 8.5 volts to turn on rx. I pulled tr36 and 37 and checked them on my b&k tester and they are fine even the leakage is fine. So i tried injecting signal into the audio chip and i just hear a low signal if i put my ear up to the speaker. So i replaced the audio chip and still no ops. I also check the speaker jack in the back it is fine also. i replaced c145, C146, C150, AND C151. Still no audio. fixed a couple of solder joints. Still no ops. starting to see a pattern here yet ha ha ....... oh well lets continue anyway. I check tr42 and it is ok also. tried injecting a audio signal agian no luck with that eather. I will list some voltages that i have on my NEW adio chip so far. I will also list some other ic's and transistor voltages. keep in mind i have no rx but tx does work.
TR36 RX E 8.7V C 0V B 8.2V
TR36 TX E 8.7V C .7V B 8.2V
TR37 RX E 0V. C 8.1 B 0V
TR37 RX E 0V. C 8.1 B 0V.
well thats what i have so far hopefully somebody can shed some light on this little issue.
thanks,
MIKE
Your problem is here,
TR36 RX E 8.7V C 0V B 8.2V
TR36 TX E 8.7V C .7V B 8.2V
TR36 collector needs to be 8v in RX and 0v in TX
TR38 collector needs to be 0v in RX and 8v in TX
Something is causing TR36 to hang and without 8 volts on the collector you will not have RX.
This is normally caused by varactor diode D77 p/n MA27T leaking or shorted.
So look at D77, TR36 and TR37 first.
It can also be caused by diodes D81/D82 but that's not the case since your voltages on IC4 look good.
I got the rx turn on voltage on tr36. sorry if i did not mention that before. So that part of the radio is fine now i just have to find out why my receive section is not working and also i have no audio. I have lifted one leg of D80 and no dice. I have also replaced the audio ic ta7222ap and the corresponding elecrolytic caps. I replaced the squelch chip also and still same problems. I did notice that the meter slams and i have to turn the rf gain down now when the radio is on to keep from damaging the meter. I want to concentrate on getting my audio back first then move on to the receiver side. I will try what you said rick thanks.
OK I got my audio back now it was actually a bad ground for the switch that controls the speaker ground on your am fm or pa switch. whew now that that issue is resolved we can move onto the next issue.
I dont have any rx. I injected a mudulated signal into the radio and went up to .83mv and still no audio not even faint. So i checked the squelch switch and it has these voltages. TR16 Base .8 volts colector and emitter are both at 0 volts. Acourding to the voltage chart that is only when the radio is squelched or in tx mode. the squelch is turned all the way down. The meter also is almost slammed clear to the left in rx mode also. Something appears to be wrong in the suelch amp section somewhere. Keep in mind the voltage regulator was putting 13.8 volts to the ic,s in the radio. I changed the squelch amp and still does the same thing. I am going to do somemore troubleshooting for now. If anybody has any ideas let me know what you think.
Alright well were almost got it now. I lifted the collecor on tr16 and i have audio now but it is a 2 khz or so tone on there now and i dont have any ant hooked up. I lifted d11 so it must be in the rx section somewhere. I am going to look into that now. then figure out why the squelch is not working. thanks for the tip rick like alway very helpful hints. thanks to everyone for the informaition.
Well i lifted D11 like i said before and the tone 2k tone goes away. I lifted C22 and C21 and the tone goes away. so I am getting this tone somewhere in the rx section. A hunting i will go
I GOT IT. I forgot to check my voltages on tr38 and since transmit was working i never gave it another thought. well after I chased my tail a while i traced the problem back to the carrier oscilator. it was not turning off during rx. So i checked my voltage and one voltage on the transistor was supposed to be 0 volts in rx was about 4.5 volts. I found that D77 was bad. replaced it and my sguelch came back and rx works perfect. I am getting .20 uv @ 10db sinad. Not bad for a beat up radio. Everyting is working great now thank you for all your input guys.
....... oh well lets continue anyway. I check tr42 and it is ok also. tried injecting a audio signal agian no luck with that eather. I will list some voltages that i have on my NEW adio chip so far. I will also list some other ic's and transistor voltages. keep in mind i have no rx but tx does work.
