06-07-2013, 11:01 PM
Onward and upward, ish.
Having persuaded the Timebase to work, at least most of the time, there was still one thing that was driving me bonkers - the Trace kept dashing off North or South. The Shift Pot would get it back but it was entirely unhelpful. So, what's the problem? As expected the Y-Amps are pretty complex as it's 2 Channel and does A, B, Chop and Alternate. There's also AC/DC Input switching, Normal/Invert for each Channel, the Input Attenuators, shifts and finally the Calibrated Shift. There's also a job lot of Presets. The obvious starting point seemed to be to try all the Controls, and sure enough the B-Channel Normal/Invert Switch, the one I was using, was solid. Well, it's got to be fixed at some stage so it might as well be now. There are two of these switches, one for each channel, side-by-side with the engraving in the middle, so they're a mirror image of each other. The circuit is quite simple in that the switch selects the output from a pair of (balanced) Cathode Followers. The Switches themselves are quite a long way back in the chassis, and are operated via an extension shaft and a Coupler. Oddly, while all the other Switches are normal open frame ones these aren't. The Coupler sits in a slot in the Chassis. Accessibilty is not it's strongpoint as the B Channel Switch is the 'Bottom' one when looking from the side. Step one was to remove the Knob, Shaft and Coupler to see what's what. It's all held together with 6BA Socket Head Grub Screws. Slacking the Grub Screws wasn't too difficult but the Knob was stuck on the Shaft and the Shaft was stuck in the Coupler, at least as far as pulling it out was concerned. After a strong dose of PlusGas, and using tools not normally associated with Electronic Equipment, I got them out. The Gods must have been with me 'cause I dropped one of the Grub Screws and found it again. However, that didn't help a lot as the Coupler couldn't be removed due to the slot in the Chassis, and there wasn't room to get a grip on the Switch Shaft with anything sensible. The first two Attached pictures show it with the Extension Shaft removed but with the Switch in situ - it's the bottom one.
That was yesterday, and today my mate Pete turned up. He's got smaller hands than me and he's Left Handed, which has its advantages. However, despite slackening the Pot that's above it and swinging it out of the way we still couldn't get a grip on the Shaft, so out it had to come. Fortunately, the wiring is quite simple and symetrical, and it's all on one side of the Chassis. Having disconnected the wiring the nut was removed by the old expedient of tapping it round with a long Screwdriver and a small Hammer, and it was out - see Picture 3. However, it was still solid. Another dose of Plusgas and oil, removal of the 'Wafers' and some gentle easing in the Vice got it going. After that it was just a matter of putting it all back together, including all the Valves we'd taken out, and switching on. There was one small panic as some smoke appeared, but it turned out to be some PlusGas, Servisol or 3-in-1 burning off.
So, was it a success? In a nutshell no. OK, the Switch now operates, in fact it feels better than the A-Channel, but it's still dodgy, at least as far as getting a Trace is concerned, although once it's there it doesn't rush off as before.
Further investigations showed that the Input Attenuator Switches don't seem to have all 7 postions so the Knobs are currently off and the shafts are soaking.
Tomorrow's another day.
Alan
P.S. No ticking, so perhaps it was just a bit of damp
Having persuaded the Timebase to work, at least most of the time, there was still one thing that was driving me bonkers - the Trace kept dashing off North or South. The Shift Pot would get it back but it was entirely unhelpful. So, what's the problem? As expected the Y-Amps are pretty complex as it's 2 Channel and does A, B, Chop and Alternate. There's also AC/DC Input switching, Normal/Invert for each Channel, the Input Attenuators, shifts and finally the Calibrated Shift. There's also a job lot of Presets. The obvious starting point seemed to be to try all the Controls, and sure enough the B-Channel Normal/Invert Switch, the one I was using, was solid. Well, it's got to be fixed at some stage so it might as well be now. There are two of these switches, one for each channel, side-by-side with the engraving in the middle, so they're a mirror image of each other. The circuit is quite simple in that the switch selects the output from a pair of (balanced) Cathode Followers. The Switches themselves are quite a long way back in the chassis, and are operated via an extension shaft and a Coupler. Oddly, while all the other Switches are normal open frame ones these aren't. The Coupler sits in a slot in the Chassis. Accessibilty is not it's strongpoint as the B Channel Switch is the 'Bottom' one when looking from the side. Step one was to remove the Knob, Shaft and Coupler to see what's what. It's all held together with 6BA Socket Head Grub Screws. Slacking the Grub Screws wasn't too difficult but the Knob was stuck on the Shaft and the Shaft was stuck in the Coupler, at least as far as pulling it out was concerned. After a strong dose of PlusGas, and using tools not normally associated with Electronic Equipment, I got them out. The Gods must have been with me 'cause I dropped one of the Grub Screws and found it again. However, that didn't help a lot as the Coupler couldn't be removed due to the slot in the Chassis, and there wasn't room to get a grip on the Switch Shaft with anything sensible. The first two Attached pictures show it with the Extension Shaft removed but with the Switch in situ - it's the bottom one.
That was yesterday, and today my mate Pete turned up. He's got smaller hands than me and he's Left Handed, which has its advantages. However, despite slackening the Pot that's above it and swinging it out of the way we still couldn't get a grip on the Shaft, so out it had to come. Fortunately, the wiring is quite simple and symetrical, and it's all on one side of the Chassis. Having disconnected the wiring the nut was removed by the old expedient of tapping it round with a long Screwdriver and a small Hammer, and it was out - see Picture 3. However, it was still solid. Another dose of Plusgas and oil, removal of the 'Wafers' and some gentle easing in the Vice got it going. After that it was just a matter of putting it all back together, including all the Valves we'd taken out, and switching on. There was one small panic as some smoke appeared, but it turned out to be some PlusGas, Servisol or 3-in-1 burning off.
So, was it a success? In a nutshell no. OK, the Switch now operates, in fact it feels better than the A-Channel, but it's still dodgy, at least as far as getting a Trace is concerned, although once it's there it doesn't rush off as before.
Further investigations showed that the Input Attenuator Switches don't seem to have all 7 postions so the Knobs are currently off and the shafts are soaking.
Tomorrow's another day.
Alan
P.S. No ticking, so perhaps it was just a bit of damp
