Hi guys , up next on my work bench is a old Simpson 955 multi meter , I was going through it this morning and found one of the bobbin resistors has failed , from what is remaining of the wire on it I'm testing around 7.5 ohms but really need to see a schematic to know for sure what to replace this part with ..
Really hoping someone has information on this meter because I can't find anything on it anywhere , must not have been a very common meter .. cheers Roger
Really hoping someone has information on this meter because I can't find anything on it anywhere , must not have been a very common meter .. cheers Roger
Doing a little research and I believe these little bobbin resistors are hand wound to tune the meter . My buddy has some of them that I can take apart , I figure if I can find a closely matched piece of resistor wire longer then needed I can keep shortening it until the meter comes closely into calibration , then just wrap it on the bobbin . Must of been what they were doing when they made the meters because they have no pots to adjust , I guess one could also get it close and add a pot across the resistor to fine tune the setting ..
so I was able to track down some old electronic switches with the wire wound resistor bobbins , thanks Alden . I now have a variety of wire diameters to choose from so I just closely matched the new wire to the wire I removed from the burnt out bobbin ..From the remaining pieces of burned wire on the old bobbin I determined that the resistance must be in the 3ohm range so started with a length of wire that measured 4 ohms . This resistor was controlling the centering of the ohms scale dial so I just continued to reduce it's length until I was able to gain control of the zeroing in all the different ohms settings . Turned out to be 3.65 ohms to make the meter settle in .. I did notice the large ceramic resistors for the 5000v scale were open so I just removed them , they lead to different inputs so it has no affect on any function I will ever use . She seem to work perfectly now . Been doing all the testing with the D cell for the 1.5 v and my little HP power supply for the 30v so I guess I am going to have to purchase one of those crazy expensive 30v batteries . in Canada they want $40-$50 for one of them . I've seen one guy use 3x9v batteries and though in this meter they would not fit the battery compartment it would likely have enough room to mount them in the case someplace ..cheers
