Radiometer SMG40 basic testing and calibration. - UK Vintage Radio Repair and Restoration Discussion Forum

djsbriscoe · 11th Nov 2018, 9:40 pm

Just bought myself a Radiometer SMG40 stereo generator.

I have fixed the Composite level meter which was reading full scale deflection at switch on and was unresponsive.The LM311 comparator chip in the peak detector was defective so I replaced it and added an 8 pin socket as well. I guess someone put a signal INTO the output socket and it destroyed the chip.

I am beginning to work my way through the service manual. It has a comprehensive series of checks and adjustment procedures. I can carry out most of the DVM and scope tests apart from the distortion ones as I don't have a distortion meter.
It also mentions a wave analyser. I'm guessing this is the same as a spectrum analyser which I have access to to at work (HP E4402B 9K - 3G) but I don't know how to use it yet. So here is a chance to learn I suppose.

Has anyone done a full test and calibration of one of these generators? Can I get away with not using a distortion meter or is there a workaround for this?
Thanks.

PS I have read Mark Hennessey's info about his SMG40. Very interesting.

djsbriscoe · 13th Jan 2019, 8:51 pm

Currently replacing the various Frako Electrolytic capacitor with new Vishay axial types. Also replacing the tantalum capacitor in the Pilot integrator as the Pilot sync output signal is distorted and occasionally changes frequency.
Also bought myself a Signal Hound SA44B/TG44A spectrum analyser/tracking generator to help test it.

djsbriscoe · 26th Jan 2019, 11:56 am

Had to replace the 7404 hex inverter chip in the oscillator as the pilot frequency was jumping around when I switched the unit on and off. One of the hex inverters (input pin 11) had probably been damaged by power surges from the power supply and a sign that I've probably replaced the power supply capacitors just in time. The frequency has changed by a fraction of a Hertz but is still within the +/- 1Hz spec.
Got to carry on working my way through the service manual.

djsbriscoe · 27th Jan 2019, 12:48 pm

This was not needed as the problem remains. I am now looking to replace the clock with a Si5351a clock. Hopefully I can generate a 4.56MHz, 2.28MHz or 228KHz clock signal that is a bit more stable. I suspect the existing crystal is being forced into an overtone or something (can someone enlighten me on this-I don't know much about 7404 based crystal oscillators).

11th Nov 2018, 9:40 pm	#1
djsbriscoe Pentode Join Date: May 2015 Location: Hemel Hempstead, Hertfordshire, UK. Posts: 133	Radiometer SMG40 basic testing and calibration. Just bought myself a Radiometer SMG40 stereo generator. I have fixed the Composite level meter which was reading full scale deflection at switch on and was unresponsive.The LM311 comparator chip in the peak detector was defective so I replaced it and added an 8 pin socket as well. I guess someone put a signal INTO the output socket and it destroyed the chip. I am beginning to work my way through the service manual. It has a comprehensive series of checks and adjustment procedures. I can carry out most of the DVM and scope tests apart from the distortion ones as I don't have a distortion meter. It also mentions a wave analyser. I'm guessing this is the same as a spectrum analyser which I have access to to at work (HP E4402B 9K - 3G) but I don't know how to use it yet. So here is a chance to learn I suppose. Has anyone done a full test and calibration of one of these generators? Can I get away with not using a distortion meter or is there a workaround for this? Thanks. PS I have read Mark Hennessey's info about his SMG40. Very interesting. Last edited by djsbriscoe; 11th Nov 2018 at 9:56 pm.

13th Jan 2019, 8:51 pm	#2
djsbriscoe Pentode Join Date: May 2015 Location: Hemel Hempstead, Hertfordshire, UK. Posts: 133	Re: Radiometer SMG40 basic testing and calibration. Currently replacing the various Frako Electrolytic capacitor with new Vishay axial types. Also replacing the tantalum capacitor in the Pilot integrator as the Pilot sync output signal is distorted and occasionally changes frequency. Also bought myself a Signal Hound SA44B/TG44A spectrum analyser/tracking generator to help test it.

26th Jan 2019, 11:56 am	#3
djsbriscoe Pentode Join Date: May 2015 Location: Hemel Hempstead, Hertfordshire, UK. Posts: 133	Re: Radiometer SMG40 basic testing and calibration. Had to replace the 7404 hex inverter chip in the oscillator as the pilot frequency was jumping around when I switched the unit on and off. One of the hex inverters (input pin 11) had probably been damaged by power surges from the power supply and a sign that I've probably replaced the power supply capacitors just in time. The frequency has changed by a fraction of a Hertz but is still within the +/- 1Hz spec. Got to carry on working my way through the service manual.

27th Jan 2019, 12:48 pm	#4
djsbriscoe Pentode Join Date: May 2015 Location: Hemel Hempstead, Hertfordshire, UK. Posts: 133	Re: Radiometer SMG40 basic testing and calibration. This was not needed as the problem remains. I am now looking to replace the clock with a Si5351a clock. Hopefully I can generate a 4.56MHz, 2.28MHz or 228KHz clock signal that is a bit more stable. I suspect the existing crystal is being forced into an overtone or something (can someone enlighten me on this-I don't know much about 7404 based crystal oscillators).