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Super Galaxy Intermittent Transmit Problem. Any Ideas?

JB383RI

Member
Jul 2, 2021
10
1
13
RI
Hey everyone! I'm looking for some help on a super galaxy mobile. I'll try to provide as much detail as possible.

The PCB number is worn off but I believe it is a EPT3600-xxx

When the radio is first turned on and you key the mic, it will transmit at full transmit power for a split second then lose transmit power but the radio stays in transmit. Then, once you key the radio again, it will switch into transmit but there is no transmit power in any mode no matter how many times I try to key it. I have to turn off and unplug the radio and wait over an hour to try it again, then rinse and repeat to try and find the problem.

So far I have replaced all the electrolytic capacitors.
I replaced the driver transistor "TR44" and both finals "TR43 and TR56" with a NOS Mitsubishi 2SC2166 and two 2SC2312's.

I have the service manual and have checked voltages through out the radio and everything seems to be correct except for a few things.

Final TR43, Driver TR44, AM Mod Amp TR49, AM Mod Amp TR50, AM Mod Amp TR51, and Final TR56, all have the correct voltages when the radio is working correctly but when I lose transmit power I also lose these voltages.

Also with the TX Mixer IC9 everything is correct when the radio is working correctly, but when I lose transmit power I lose the voltage on Pin 1.

Just some additional info - I always have receive, if I switch to PA mode I always have modulation, and sometimes it will stay keyed up with power and modulation for as long as I keep it keyed then it goes right back to only working for a split second. It also doesn't matter what mode I'm in its all the same.

I'm just wondering if anyone has run into a problem like this before or has any ideas. If you need more information or would like me to upload pictures please ask. Thanks in advance everyone.
 

I doubt that it's worn off. On those radios they didn't silk screen the numbers onto the board, but they were actually part of the etching process and were on the solder side along the front edge of the radio next to the meter.
Like this...
1649015496032.png
 
Last edited:
Siding with SP5it - and 999 - you may have replaced the caps, but you'll need to check the RED/GREEN TX/RX light - if it's RED and stays red, but you lose power - you may have more work in there regarding a cap or two.

But if the RED/GREEN light goes dark, then you're out of lock and you'll need to investigate the VCO section see if it needs some re-alignment - not all the caps replaced bring back a radio - you'll have to tweak the coils to see if the previous owners messed with it and tried to fix it themselves - that is a far bigger problem - undoing what they did so you can fix it, right.
 
I doubt that it's worn off. On those radios they didn't silk screen the numbers onto the board, but they were actually part of the etching process and were on the solder side along the front edge of the radio next to the meter.
Like this...
View attachment 58282
Mine is not like that. With the radio upside down it looks like it used to be on the left hand side in between TR41 and IC8. There is part of a E and what looks like it used to be an A at the end. My guess is its a EPT3600-10A
 
Siding with SP5it - and 999 - you may have replaced the caps, but you'll need to check the RED/GREEN TX/RX light - if it's RED and stays red, but you lose power - you may have more work in there regarding a cap or two.

But if the RED/GREEN light goes dark, then you're out of lock and you'll need to investigate the VCO section see if it needs some re-alignment - not all the caps replaced bring back a radio - you'll have to tweak the coils to see if the previous owners messed with it and tried to fix it themselves - that is a far bigger problem - undoing what they did so you can fix it, right.
I understand caps are not always the solution. I had changed all the caps because one of them in the frequency counter was leaking.

The TX/RX light stays RED even when I lose the carrier.

I have the proper VCO voltage.

It doesn't seem to unlock I never lose receive and Pin 8 on MC145106 never goes to 0 Volts. Its always +8 VDC
 
Then once VCO is verified ok, the other issue is with the toggle function back at IC4 - that little 4558 chip - one side is Mic audio amp, but the other is the RX/TX switch that uses VCO, 8V regulated and Mic key condition to toggle a pair of transistors - one from ON to OFF the other OFF to ON

So check the output of IC4 (it may be something else - not sure of board type presuming EPT360011 or thereabouts) by looking at the TX Mixer output coil in the TX strip side.

If you have output the issue may be an open bias resistor network in one of the pre-driver / buffer amps, you'll need to test transistor voltages at the leads.

If it's TX power to it goes on it may force a transistor on, but with too much voltage - then it's overdrive - like a switch and works like a DC switch, but not an RF one (too much RF will make subsequent stages see nothing but distorted power to a point) it looks like noise and it just stays on - but produces no RF.

Because it's biased wrong.
 
Then once VCO is verified ok, the other issue is with the toggle function back at IC4 - that little 4558 chip - one side is Mic audio amp, but the other is the RX/TX switch that uses VCO, 8V regulated and Mic key condition to toggle a pair of transistors - one from ON to OFF the other OFF to ON

So check the output of IC4 (it may be something else - not sure of board type presuming EPT360011 or thereabouts) by looking at the TX Mixer output coil in the TX strip side.

If you have output the issue may be an open bias resistor network in one of the pre-driver / buffer amps, you'll need to test transistor voltages at the leads.

If it's TX power to it goes on it may force a transistor on, but with too much voltage - then it's overdrive - like a switch and works like a DC switch, but not an RF one (too much RF will make subsequent stages see nothing but distorted power to a point) it looks like noise and it just stays on - but produces no RF.

Because it's biased wrong.
Thanks for the info and suggestions Andy. Ok so trying to follow your ideas. I have the proper voltages at IC4 "Mike Amp and T/R Switch, TR-36, TR-37 both of which are RX Voltage Switch and TR-38 the TX Voltage Switch. Also TR-45 "RF Pre-driver" and TR-46 "RF Amp & Buffer seem to have the correct voltages as well. So far the radio is still doing the same thing. Also sometimes on the first Key-up the radio will stay keyed, have perfect power and modulation for as long as I keep it keyed but once I un key the radio and key it again it will still switch to transmit but have no output power. Its also tough not having an oscilloscope.
 
good luck dude. about half way thru your issue i thought it was same as mine,,NOPE! Wish great luck and these guys/gals are great, they'll help you. Ray
Lol this is a tough one. Plus it sucks being intermittent and having to wait sometimes over an hour for the radio to start working again only to have it die after the first key. I know you said yours was a different problem but I'm just curious what your problem was.
 
Also for what its worth with a Frequency Counter at the collector of TR-45 "RF Pre-driver" I have on CH. 1 26.9650 MHz. I also have that at the collector of TR-44 " Driver".
 

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