Help with FT200 No IC reading on Tx - UK Vintage Radio Repair and Restoration Discussion Forum

Chris G0EYO · 21st Feb 2010, 3:53 pm

Hi I am inexperienced when it comes to fault finding on transmitters. I am restoring the club's FT200 and have got the receiver side working nicely. On transmit you are required to check the IC is about 60mA with the FUNCTION switch on SSB and the OPER-REC switch in Operate. Problem is I get no reading at all on the meter in this configuration. Tuning then requires that you switch the FUNCTION switch to TUNE and adjust MIC control and check the IC is reading about 100mA. Again I get no meter reading.

Has anyone got any ideas. I have traced the circuit through for the meter and all seems ok, I have adjusted the bias but no change. The voltages on the PA stages seem ok. I have already replaced the troublesome C55 and C40 HV caps. On receive the meter has about 1.6V across it after warm up and with no signal. When I switch to OPER the volts across the meter drops to 0V.

Most of my electronics has been theory with very little practical experience. I can find my way around a circuit ok but it takes me time to work out what is going on and what checks I should be doing.

Any advice would be appreciated. I have attached a copy of the circuit. Just love the Japanese tramlines!!

Chris G0EYO
Wythall Radio Club

Don Collie jnr · 22nd Feb 2010, 8:25 am

You could carefully put a meter across the meter shunt in the cathode circuit.
Ohms law will tell you what you should expect. If this voltage is approximately correct, your problem is between this resistor and the meter. If not you must take your life in your hands [literally], and measure the electrode Voltages around the 6JS6C`s - be darn careful, and measure anode volts last. I take it the ALC/IC switch is in the correct position for measuring Cathode current?.......................................... ...............................Don.

Chris G0EYO · 22nd Feb 2010, 11:32 am

Thanks Don

I found the meter shunt resistor, looks like a wirewound resistor on ceramic former, measured it at about 1.2 ohms. Measured the volts across it when Ic quiescent, in OPER, it read 1.1mV (using DVM). Switched to TUNE and adjusted MIC GAIN and volts went up to 60mV+ and rising as I increased MIC GAIN. Using ohms law I work out that the current through the shunt resistor is 0.9mA on Ic quiescent and 50mA plus as MIC GAIN increased in TUNE. This indicates that the meter is not in circuit and the likely suspect is RL101 but I will check the wiring again when I have worked out the pin connections on the relay base. I wonder what sort of volts I should be reading across the shunt resistor. Need to think about that one a bit more

Regards

Chris G0EYO

Don Collie jnr · 23rd Feb 2010, 10:07 am

Good luck Chris!,........................................... ..........................................Don.

22nd Feb 2010, 8:25 am	#2
Don Collie jnr Retired Dormant Member Join Date: Jul 2008 Location: Invercargill, New Zealand Posts: 51	Re: Help with FT200 No IC reading on Tx You could carefully put a meter across the meter shunt in the cathode circuit. Ohms law will tell you what you should expect. If this voltage is approximately correct, your problem is between this resistor and the meter. If not you must take your life in your hands [literally], and measure the electrode Voltages around the 6JS6C`s - be darn careful, and measure anode volts last. I take it the ALC/IC switch is in the correct position for measuring Cathode current?.......................................... ...............................Don.

22nd Feb 2010, 11:32 am	#3
Chris G0EYO Pentode Join Date: Dec 2008 Location: Redditch, Worcestershire, UK. Posts: 196	Re: Help with FT200 No IC reading on Tx Thanks Don I found the meter shunt resistor, looks like a wirewound resistor on ceramic former, measured it at about 1.2 ohms. Measured the volts across it when Ic quiescent, in OPER, it read 1.1mV (using DVM). Switched to TUNE and adjusted MIC GAIN and volts went up to 60mV+ and rising as I increased MIC GAIN. Using ohms law I work out that the current through the shunt resistor is 0.9mA on Ic quiescent and 50mA plus as MIC GAIN increased in TUNE. This indicates that the meter is not in circuit and the likely suspect is RL101 but I will check the wiring again when I have worked out the pin connections on the relay base. I wonder what sort of volts I should be reading across the shunt resistor. Need to think about that one a bit more Regards Chris G0EYO

23rd Feb 2010, 10:07 am	#4
Don Collie jnr Retired Dormant Member Join Date: Jul 2008 Location: Invercargill, New Zealand Posts: 51	Re: Help with FT200 No IC reading on Tx Good luck Chris!,........................................... ..........................................Don.