Galaxy Saturn no tx power

[Spyedar]

I have a Galaxy Saturn that has had a fairchild MOSFET conversion done on it, it has no tx power, no watts, already replaced TR40, 41, 49, 50 and TR51. When you key up the lights dim significantly also

[Bozo]

It sounds like you're dealing with a significant power issue. The dimming lights when you key up suggest a heavy current draw, which could indicate a short or a problem in the power supply or final stages of the RF section. Here are some steps you can take to troubleshoot this:

1. Check Voltage at Key Components: Measure the voltage on the MOSFETs and transistors you replaced, especially around the final stages. Ensure they’re receiving proper voltage, as a significant voltage drop could prevent the transmitter from generating power.


2. Inspect the Power Supply Circuit: Since the lights dim, it’s likely there’s an issue with the power circuit. Ensure capacitors in the power supply area are in good condition, as bad caps could fail under load, causing a voltage sag.


3. Double-Check Ground Connections: Poor grounding can lead to significant issues, especially with MOSFETs. Make sure that all grounding connections around the MOSFETs and transistors are solid.


4. Examine for Shorts in the Output Stage: There may be a short somewhere in the output section of the RF stage. Look around the output transformers and associated circuitry for any possible shorts or components with very low resistance.


5. Bias Settings: Ensure the bias for the new MOSFET is set correctly. If it’s too low, it might prevent the MOSFET from turning on properly, and if it’s too high, it could cause excess current draw.


6. Check for Cold Solder Joints: Inspect all solder connections around the replaced transistors and MOSFETs. A cold solder joint can cause intermittent issues, like excessive current draw or a loss of power.


7. Inspect TR52: The TR52 transistor might be involved in the TX power circuit. Since you've already replaced some transistors, this one could also be worth checking, as it might interact with the TX circuitry.



Given the symptoms and the components you’ve already replaced, these steps should help you get closer to the root of the problem. If none of these seem to resolve it, there may be an issue with the output transformer or a related component in the final stages that’s causing excessive current draw.


Good luck

[Spyedar]

TR52 is the SSB audio switch if my info is correct it's from the 1995 Saturn service manual

[MDYoungblood]

I no longer work on radios but if the radio is dimming as said, the power supply is one of the problems. I don't remember if that radio has an external power plug or not. I couldn't find any info on the final conversion but there still is a kit with instructions on the internet, it is interesting and I am thinking of buying one the dual final kit for my ranger mobile just to play with.

Good luck at figuring it out.

3's

Greg

[Spyedar]

I no longer work on radios but if the radio is dimming as said, the power supply is one of the problems. I don't remember if that radio has an external power plug or not. I couldn't find any info on the final conversion but there still is a kit with instructions on the internet, it is interesting and I am thinking of buying one the dual final kit for my ranger mobile just to play with.

Good luck at figuring it out.

3's

Greg

External power plug? If you mean plugs into the wall, it does, it's got a three prong plug, it had a 2 prong but I changed it to a 3 prong to add extra grounding, and that worked great, it was quieter on receive after.

[MDYoungblood]

No, I meant a 12v plug for an external power supply.

I have a early model 2995 that I replaced the amp with a 8 mosfet unit and had to upgrade the internal supply with a larger MeanWell brand switching supply, worked great and no more dimming lights. I believe Megawatt sells supplies for inside the radios and is a sponsor here on the forum. I would have purchased from him but I did the mods long before he came along.

3's

Greg

[Spyedar]

Yeah I'm going to re-cap the power PCB's, both of em', and the ones I can I'll change to a 3kV of the correct farad value