View Single Post
Old 27th Jan 2021, 7:08 pm   #91
em536716
Hexode
 
em536716's Avatar
 
Join Date: Dec 2017
Location: South East London
Posts: 301
Default Re: My newly found Marconi 707

Thanks all for the comments about the pots. Andy has now sent me the spares one to fit so spent the afternoon doing this.

The radio portion of the set is now alive and kicking and receiving well, I thought I would move my attention onto the vision side of things.

I replaced the 2 domino capacitors feeding the grids of the timebase and proceeded to apply power. I was gifted with strong line whistle, and could hear the frame timebase purring away, but wasn’t getting any raster on the tube.

R41 started burning up and eventually went open circuit. A quick power off, and a search for the shorted cap started. I had already replaced C23, but I think I’ve found the culprit. The shorted cap was behind the brightness/contrast pots, both C3 and 4 were both under 500 ohms, but the location on the schematic had nothing to do with R41 anyway. There’s very few original caps left now, so even though the short is cleared I’ll be cautious. I’ll come back to this.

R41 is now replaced so now it’s time to work on the TV side of things. I’ll post some updates when I get something on the tube!
__________________
With regards,
Ed
em536716 is offline