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Heatercathodeshort · 2nd Jul 2020, 12:52 pm

The Onwa chassis was ruined by just two cheap 47uf capacitors in the power supply. The important one was in the voltage sensing circuit. It went O/C or partly so causing the H.T. to rise eventually destroying the line output transistor. It was then brought in for repair.

By then it had over run the tube heater resulting in a flat picture when the heater was supplied with the correct voltage. It was powered from the line output stage.

This fault also occurred on certain Goodmans chassis and others so it was not unique to Onwa. I could not believe it when I discovered the chassis was also fitted in a JVC!

This could not happen with Matsui and Saisho models due to the 'cowbar' R2M diode across the H.T. line. Just one single cheap diode would have saved a mess.Where do the years go? John.

2nd Jul 2020, 12:52 pm	#13
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Matsui saved... The Onwa chassis was ruined by just two cheap 47uf capacitors in the power supply. The important one was in the voltage sensing circuit. It went O/C or partly so causing the H.T. to rise eventually destroying the line output transistor. It was then brought in for repair. By then it had over run the tube heater resulting in a flat picture when the heater was supplied with the correct voltage. It was powered from the line output stage. This fault also occurred on certain Goodmans chassis and others so it was not unique to Onwa. I could not believe it when I discovered the chassis was also fitted in a JVC! This could not happen with Matsui and Saisho models due to the 'cowbar' R2M diode across the H.T. line. Just one single cheap diode would have saved a mess.Where do the years go? John.