Before I Drive Myself Nuts!!

[Yorkie]

Ok,
Using an Avo 7 (I must use this more so please excuse me if I am reading this incorrectly - lesson for me here) with the AC set to resistance and DC set to ohms, across the mains leads is zero R (switch off) and a shade under 200R (needle to the rhs of meter) with the switch on. From the body of the dual cap (I assume you mean the reservoir cap) the resistance is also just under 200R. Dose this suggest that I have a short to earth somewhere on the ht side?

Thanks

Rob

Firstly Rob, when you say 'zero Ohms' do you actually mean just that? IE, do you get the same reading as you would if you shorted the test prods together, indicating a dead short (needle of the meter full scale deflection to the RH side? If so, that indicates a dead short, and yes, you've wired the switch wrong. Or do you mean you get 'no reading' - IE, the needle doersn't move at all, in which case that isn't 'zero Ohms' but infitinty - an open circuit in other words.

Just to be clear about how the two pole mains switch (S2 on the circuit), should be wired, see the attached diagram.

If you've wired it correctly, any problems aren't with the switch, but downstream of it. Looking at the circuit, if all was well, you have two 200 Ohm resistors (R35 & R36) in series with the heaters (assuming you have the mains tap set to 240V), so there is at least 400 Ohms, plus the total resistance of seven valve heaters in series. If - as you say - you've changed all the caps that would normally be changed, you shouldn't have any leakage to the chassis on the HT side, so if all is well, the resistance across the mains input with the switch closed, should certainly be in excess of 400 Ohms. C60 (across the mains input) should be a Class X cap, and really, you'd be better off without it as Steve has said - you won't notice any difference.

You mentioned the AVO7 Rob, and that 'you must use it more'. If you do, it will lead you a merry dance, and often give misleading results. Whilst the Avo 7 is fine for checking resistances or current, and voltage in certain circumstances, it's a most unsuitable instrument for radio and TV servicing work, because it only has an input impedance of 1,000 Ohms per Volt. (AVO 8 is 20,000 OPV). I don't want to muddy the waters of this thread, so I'll post something about that in another thread.

A nice collectors' item on the shelf, but best not used in radio work.

Hope that helps a bit Rob - best of luck with the VHF90.

Keith Wevill (AKA 'Keith's TVs') gave an excellent talk at the Golborne Swapmeet last Sunday in which he explained the effects of various multimeters in diagnostic work, and in the use of 'Scopes. He has since sent the notes of his talk to those who attended, and I've been in touch with Keith to request his permission to place the notes on the forum, which he has granted, so long as we credit him as being the author, as of course we will. Keith's talk was excellent, and the notes are very well written and illustrated, so I'll upload them shortly now that we have Keith's kind permission.