I'm trying to repair an inverter board for a mechanical gyroscope (the gyro is a J.E.T. AI-904, 501-1170-02, and the board converts 28VDC to 3-phase 400Hz AC). I do not have schematics or parts list. I've been able to figure out 2 defective parts in the leg that doesn't work: one is a UA748H opamp, for which I have found a replacements.
The other part appears to be a transistor in a TO-12 case with faded markings and obvious overheat discoloration. As best as I can tell under a microscope, it's labeled "7943" and "U21101". An extensive internet search has come up empty.
My transistor tester sees it as 2 diodes, with Uf=659 & 748mV.
Other similar case devices in the circuit, without labels, are identified as PNP with B=82 and Uf=670mV. I'm not sure all the parts are the same. The other legs are all sealed in a gelatinous substance that's impossible to remove without possible damage to the components, so that route is not open.
Any help from you smart guys about the mystery 7943 part would be greatly appreciated.
A schematic for the gyro would win you accolades and a small token of appreciation!!
Thank you one & all.
The other part appears to be a transistor in a TO-12 case with faded markings and obvious overheat discoloration. As best as I can tell under a microscope, it's labeled "7943" and "U21101". An extensive internet search has come up empty.
My transistor tester sees it as 2 diodes, with Uf=659 & 748mV.
Other similar case devices in the circuit, without labels, are identified as PNP with B=82 and Uf=670mV. I'm not sure all the parts are the same. The other legs are all sealed in a gelatinous substance that's impossible to remove without possible damage to the components, so that route is not open.
Any help from you smart guys about the mystery 7943 part would be greatly appreciated.
A schematic for the gyro would win you accolades and a small token of appreciation!!
Thank you one & all.