Levell TG200DMP - UK Vintage Radio Repair and Restoration Discussion Forum

KennyJ83 · 22nd Oct 2013, 4:57 pm

I have been having an intermittant fualt with the output when set to square wave. Its on one minute and completely gone the next.
Just wondering if anybodys had a similar fault or any tips on where to start looking for it.

ronbryan · 22nd Oct 2013, 5:29 pm

For a start, try cleaning the slide switch S3 a,b,c with Servisol and operating it rapidly. The two transistor squaring circuit (on the small pcb with two pots) has its output and +18V and -18V supplies switched by this component.

Ron

KennyJ83 · 22nd Oct 2013, 7:53 pm

Thanks ronbryan

I tried the switch first. When im not getting a signal through on the scope the switch still has the supplies going to the small pcb. Also took the two transistors and the two diodes out and they all work fine. Its a weird one

ronbryan · 22nd Oct 2013, 10:14 pm

Can you confirm that S3a is making good contact - this switches the output of the Schmitt trigger to the output amp when Square is selected.

Otherwise you will have to trace the signal through the trigger circuit using a multimeter and/or scope. The two pots on the trigger pcb set the amplitude of the square wave and the mark/space ratio. One of these could possibly be intermittent.

Ron

KennyJ83 · 23rd Oct 2013, 12:59 pm

Thanks Ron

I gave the switch a good spray with ultrasolve last night. Today it's been working pretty well. I took it apart to test but have yet been able to make the fault appear again. Think you're bang on about it being the switch.

Thanks for your help

22nd Oct 2013, 4:57 pm	#1
KennyJ83 Retired Dormant Member Join Date: Oct 2013 Location: Glasgow Posts: 3	Levell TG200DMP I have been having an intermittant fualt with the output when set to square wave. Its on one minute and completely gone the next. Just wondering if anybodys had a similar fault or any tips on where to start looking for it.

22nd Oct 2013, 5:29 pm	#2
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,960	Re: Tg200dmp For a start, try cleaning the slide switch S3 a,b,c with Servisol and operating it rapidly. The two transistor squaring circuit (on the small pcb with two pots) has its output and +18V and -18V supplies switched by this component. Ron

22nd Oct 2013, 7:53 pm	#3
KennyJ83 Retired Dormant Member Join Date: Oct 2013 Location: Glasgow Posts: 3	Re: Tg200dmp Thanks ronbryan I tried the switch first. When im not getting a signal through on the scope the switch still has the supplies going to the small pcb. Also took the two transistors and the two diodes out and they all work fine. Its a weird one

22nd Oct 2013, 10:14 pm	#4
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,960	Re: Levell TG200DMP Can you confirm that S3a is making good contact - this switches the output of the Schmitt trigger to the output amp when Square is selected. Otherwise you will have to trace the signal through the trigger circuit using a multimeter and/or scope. The two pots on the trigger pcb set the amplitude of the square wave and the mark/space ratio. One of these could possibly be intermittent. Ron

23rd Oct 2013, 12:59 pm	#5
KennyJ83 Retired Dormant Member Join Date: Oct 2013 Location: Glasgow Posts: 3	Re: Levell TG200DMP Thanks Ron I gave the switch a good spray with ultrasolve last night. Today it's been working pretty well. I took it apart to test but have yet been able to make the fault appear again. Think you're bang on about it being the switch. Thanks for your help