So I am new here, and just started diving into repairing my lk 203 amplifier. The amp is putting out less than 4 watts, actually almost 0 watts. It sorta worked when it was new but not well. I picked up a dummy load and a MFJ-822 wattmeter. I am using a Uniden 980 to drive the amp. My CB is putting out 4 watts on the money and swinging about 18-20VOLTS deadkey. I believe I have all the tools I need to troubleshoot this (scope, DMM, etc), but I am not exactly sure what I should be seeing on some parts.
I redrew the schematic in KiCad, so I could make better sense of it. I have made some labels to explain some sections.
So what should I be seeing on the gate of the mosfets? Now its swinging between like -3 and +8 VOLTS, which seems low. It looks like DZ1 is clamping the voltage to 20VOLTS so for the heck of it I removed D3 and D4 to remove the voltage clamp out of the circuit, and it didn't change.
The mosfets are not shorted, but I am suspecting they are bad. I cant find anything else obvious. Any recommendations on what to replace them with? IRF520N?
Any help is appreciated, I'm mostly doing this to learn about RF circuits. Thanks
I redrew the schematic in KiCad, so I could make better sense of it. I have made some labels to explain some sections.
So what should I be seeing on the gate of the mosfets? Now its swinging between like -3 and +8 VOLTS, which seems low. It looks like DZ1 is clamping the voltage to 20VOLTS so for the heck of it I removed D3 and D4 to remove the voltage clamp out of the circuit, and it didn't change.
The mosfets are not shorted, but I am suspecting they are bad. I cant find anything else obvious. Any recommendations on what to replace them with? IRF520N?
Any help is appreciated, I'm mostly doing this to learn about RF circuits. Thanks
Attachments
Last edited: