I have an older model galaxy saturn base that has power supply problems. First thing i tried was connecting it to my bench power supply and it worked as it should. Using the internal power supply it hums fairly bad, I checked the DC voltage from the internal power supply board to the main board and it showed 14.0 volts DC. I checked the DC volts out of the bridge rectifier and i'm showing 17 to 18.0 volts. When i key the mike the voltage drops to to around 9,8 or so volts going to the main board from the power supply board. I checked the 2N3055 power transistor and it is good. The 10000Uf 35vdc cap is good too at the power supply. I can put my hand on the transformer and feel the hum when i key. I dont have a scope so i cant check the bridge rectifier so i changed it. Still did the same thing. When i modulate in SSB it almost cuts off the freq. counter. I havent checked the the disc caps in the 110vac line filtering yet, I will check the resitance of that tomorrow. Any input on this?? Transformer maybe?? Thanks for any input on this!!
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Galaxy Saturn Base (Non-Turbo) Power Supply Help
- Thread starter dx77HML
- Start date
Since the 2N3055 is good, I would be tempted to disconnect the base lead on the 2n3055 and feed it 14v from my bench supply. If the radio works, the transformer and rectifier are good and the problem is in the regulator circuit. If it don't work, I would rule out the regulator and question where that replacement rectifier came from. You could probably use the same test method on the rectifier as you did to verify the transistor was good. How did you do that?
The 2N3055 was replaced with a new one. The bridge rectifier was replaced with one i had. I didnt have a new rectifier. I have 18VDC at the positive side of the rectifier. The AC voltage from the transformer feeding the rectifier is 15VAC.
An oscilloscope is the go-to tool to settle who you blame for this problem.
A bad main filter cap will reveal a lot of sawtooth-shaped "ripple" waveform feeding into the collector of the big regulator transistor.
The regulator circuit serves as a filter. It holds the DC output voltage dead steady. A failed zener, or error-input transistor (the one connected to the trimpot) will cause this even if all the filter capacitors are perfect.
We looked at the average cost to a customer to go through a failed "analog" power supply and settled on replacing it with a switchmode brick from fleabay any time the cause of the trouble isn't obvious and cheap. Saves the customer money.
73
A bad main filter cap will reveal a lot of sawtooth-shaped "ripple" waveform feeding into the collector of the big regulator transistor.
The regulator circuit serves as a filter. It holds the DC output voltage dead steady. A failed zener, or error-input transistor (the one connected to the trimpot) will cause this even if all the filter capacitors are perfect.
We looked at the average cost to a customer to go through a failed "analog" power supply and settled on replacing it with a switchmode brick from fleabay any time the cause of the trouble isn't obvious and cheap. Saves the customer money.
73
Well, after troubleshooting the power supply board in depth i found the problem, The error trasistor. 2SD471. Man, that was fun. (NOT) Thanks for all of the input!!!!