I've been using the 1062s for the last week to monitor some voltage standards I picked up. After about a week, one unit reports a min/max diff of 300uV, whereas the other reports no more than 5ppm. I took the first one out of the setup and attempted to zero the input-Error 4. Switching to manual mode, I found that the 10V ranges and higher would zero without error. This is not the same unit that I've worked on in this thread, by the way.
Today, I began the servicing process. Initial visual inspection showed that C7 on the power supply is blown out, with a hole coming out the side. I checked the 5V and 15V points and they were all fine, albeit a bit noisy. I have to recalibrate the thing anyway, so I pressed on through the check steps without changing anything too much. I'd like to continue to use it to monitor the deviation on the voltage references until a new cap arrives, so I attempted to recal the Lin, Ib and the ZERO for 0.1 and 1V DC ranges. In all instances, Error 4 is the outcome.
Although I don't have a suitable axial replacement handy, I lashed up a couple in parallel and jumpered them in across the bad cap. The bad cap was still in circuit. No improvement on the noise, auto zero or cal zero-The latter two still resulting in Error 4. Finally, I switched over to the ohms range and tried to Autozero and failed on the 10ohm range
Now is where I start scratching my head-I switched to the rear inputs, shorted Hi and Lo and was able to auto zero on the 1VDC range. The Error 4 persisted on the 10Ohm range. When I switched back to the front panel inputs, I was also able to zero the 1VDC range but not the 0.1VDC. The noise remained and was equal on both inputs.
Summary-
1) Input noise on all ranges
2) Auto zero Error 4 on 0.1 VDC, 1 VDC, and 10Ohm ranges.
-Able to auto zero on 1VDC after performing autozero using rear inputs.
3) Zero, Ib, Lin Error 4 on 0.1VDC and 1VDC ranges. Didn't attempt with ohms ranges or rear input.
Any thoughts would be appreciated. The full service manual should be linked on the first page.