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Heatercathodeshort · 21st Jun 2022, 2:05 pm

This was a very common fault with the Roberts R800 and R900. A look at the circuit will reveal C167 1500uf connected across the DC switched side from the battery/mains unit.
Switching on produces a very heavy surge and spark at the switch contacts burning them out.
The so called cure was to replace the cap, a 470uf in the R900 with 47uf. It hummmmmed! There was no other suggestion from Roberts at the time. Reducing the value of C167 in the R800 may prolong the life of the switch but it will fail again. The switch was part of a push button waveband switch in the R900. It was horrible to change!

I had a very difficult time with my customers with the 800 and 900 that led me to letting the Roberts agency go. John.

21st Jun 2022, 2:05 pm	#2
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: roberts R800 This was a very common fault with the Roberts R800 and R900. A look at the circuit will reveal C167 1500uf connected across the DC switched side from the battery/mains unit. Switching on produces a very heavy surge and spark at the switch contacts burning them out. The so called cure was to replace the cap, a 470uf in the R900 with 47uf. It hummmmmed! There was no other suggestion from Roberts at the time. Reducing the value of C167 in the R800 may prolong the life of the switch but it will fail again. The switch was part of a push button waveband switch in the R900. It was horrible to change! I had a very difficult time with my customers with the 800 and 900 that led me to letting the Roberts agency go. John.