I have an old 1740A which was displaying some odd traces at times and a while ago I took the covers off for an inspection and discovered some resistors that been overheating and burnt as well as cracking. I had to order the values as I didn't have the correct wattage ones in my parts bin so today I stripped it down and replaced them. They were on the vertical output board. In the process I also took out the power board to inspect the smoothing caps. On unplugging the secondary taps plug, pin 4 (43v rail) showed signs of overheating as well and investigating this revealed the bridge rectifier had a dodgy joint.
Resoldered the joint and also checked for other dry joints and reflowed those that looked suspect, caps all checked out just fine so reassembled everything and powered up, traces all appeared on the screen but now I'm unable to move them on the vertical position pots and there is no deflection of any sort of the traces in the vertical plane on the screen. Sweep seems to be working just fine.
Checked all the voltages on the test points all were spot on so I pulled out the vertical output board and checked it over, all seems to be normal, new resistors are not overheating etc. Refitted the board and powered up again and checked the board for all supply rails to it, and all were found to be present and spot on again. The resistors that were overheating were R2 and R4 on the attached schematic and R3 was found to within 1 ohm and so was left in situ.
Checking the voltages on Q1 and Q3 I measured 12.6V, 12V but the 0.5v measured 1.1v? I cannot get access to Q2 and Q4 as these sit behind a case strut. This 1.1v feeds directly into the hybrid A5A1 chip, has this been destroyed do you think with the voltage being doubled or can it withstand this as I see that the output voltage to CRT grids can vary between 5v to 30v depending on the vertical position pot.
I attach the schematic for reference and would appreciate any advice or guidance on this please.