Martin Lorton has undertaken the task of repairing a vintage Harmon 4200B selective voltmeter, which he obtained on eBay in good condition but non-functioning.
The 4200B is an RMS voltmeter, which requires adjustment to a particular frequency, and it contains both analogue and digital components.
Lorton’s initial tests showed that the analogue meter was stuck, only registering up to 33% of its full scale, but by the fourth video in the series, the meter was functioning correctly.
Readers can browse a similar 4200A manual to gain more insight into the model, and the comments section is a venue to share information or ask questions about the process. Chapters 4 and 5 of the manual deal with operation and calibration of the meter.
This would also be a good time to remind ourselves of the utility of RMS meters, and the various ways they have been implemented in instrumentation.
