More Datron 1071As I said in my last post about this meter, there's no such thing as a perfect one when you're talking about something from the mid '70s.
Mine was no exception, and although the meter powered up straight away when I received it and seemed to give plausible results when
reading a few voltage references and precision resistors, it was obvious that the meter wasn't entirely happy. First task was to check the
infamous Philips blue electrolytics.
Sure enough, with one end freed from the PCB, they measured:
Des. Printed Actual ESR
Value Value
C45 47μF 34μF 8.1Ω (Furthest away in the photo)
C46 47μF 34μF 6.4Ω
C47 33μF 28μF 8.1Ω
C48 33μF 25μF 10.2Ω
C49 10μF 9.7μF 4.5Ω
C50 10μF 9.4μF 7.6Ω
The replacements from Kemet and Vishay were a bit of a squeeze, but had rather better parameters:
Des. New New
Value ESR
C45 50μF 0.22Ω
C46 49.7μF 0.22Ω
C47 32.2μF 1.38Ω
C48 31.5μF 1.44Ω
C49 11.7μF 0.55Ω
C50 11.7μF 0.55Ω
I then checked the various power rails and found out of tolerance voltages and excessive ripple,
so it was time to turn my attention to that area of the meter. This is where the fun starts!
The power supply is implemented on the board that runs across the rear of the meter. Between that and the
rear of the case, Datron also crammed in all of the boards that handle the optional outputs, the front/rear
relays and the two stacked toroid transformers. It's kind of packed in there as you can see from
the photo below.
The only way I could easily work on the power supply was to separate the rear of the case with all its
boards from the rear PCB and remove the analogue, digital and current boards so that I had clear access to the
solder side of the PSU. I wasn't keen on my chances of being able to put it all back together again without
extensive photo documentation of what plug went where - there are no identifying labels on any of the plugs
that connect everything together, so I took my time and took many photos along the way. Finally, the rear
of the case was free!
continues in next post (which will be after I've eaten some strawberries and cream
)...