22-10-2011, 08:33 AM
The 1uF cap appears just a smoothing cap in the DC line. As the bridge reads 40% out on all ranges it has to be something to do with the three legs of the bridge circuit itself (the fourth leg being the cap/res under test). If you look at the circuit, it's inconceivable that the components in that part of the circuit marked A,B,C, & D are all out by the same amount - 40%. The two which are most suspect in my view are the pot, and its series cap (0.02uF) which are common to all ranges. It's unlikely to be the pot as it isn't open circuit and won't have changed in value over time, as might a carbon resistor. If we assume that the dial position on the shaft hasn't somehow slipped, which I doubt as it will have end stops, I think it more likely that the 0.02 cap is leaky and acting more like a high value resistor than a capacitor. The value of the two 1% resistors 'D & E' (1592K and 1592???) are easily checked, and the other two caps (A & B) in the bridge can be checked and replaced if need be, but wouldn't be high on my list of prime suspects.
The other thing that's puzzling Rob is that he couldn't find a rectifier diode - the original paxolin tube encased metal rectifier having been removed. As I've mentioned before, if the HT on the Y63 is perhaps 150 - 175V DC, then there must be a rectifier lurking somewhere. One end of the top winding (on the circuit) of mains transformer secondary goes to the 1uF cap, and then on to the rear wafer of the switch - the other end of that winding goes to the rectifier, then the output of the rectifier goes to ground, and the middle wafer of the switch. Hence, by tracing the connections from the lower end of the top winding, the elusive rectifier should be found!
Unlike many of us, Rob is not a man of leisure - he still has to work for a living to help to contribute to my winter fuel allowance and free bus pass, so is limited for leisure time. I guess therefore that the CRB won't be too high on his 'to do' list! Maybe when he surfaces, he'll update us on progress, if there has been any!
The other thing that's puzzling Rob is that he couldn't find a rectifier diode - the original paxolin tube encased metal rectifier having been removed. As I've mentioned before, if the HT on the Y63 is perhaps 150 - 175V DC, then there must be a rectifier lurking somewhere. One end of the top winding (on the circuit) of mains transformer secondary goes to the 1uF cap, and then on to the rear wafer of the switch - the other end of that winding goes to the rectifier, then the output of the rectifier goes to ground, and the middle wafer of the switch. Hence, by tracing the connections from the lower end of the top winding, the elusive rectifier should be found!
Unlike many of us, Rob is not a man of leisure - he still has to work for a living to help to contribute to my winter fuel allowance and free bus pass, so is limited for leisure time. I guess therefore that the CRB won't be too high on his 'to do' list! Maybe when he surfaces, he'll update us on progress, if there has been any!
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
