I have an eBay HP5328A counter with two dead digits on the display. I figured out the problem was two dead transistors. I can swap transistors with a good digit and the problem moves.
I'd not worked on LED displays before. Turns out only one digit is lit up at a time, they strobe the digits in sequence. The dead transistor is the one that controls the all the anodes in the 7-segment LED module. The service manual describes the transistor like this: "part number = 1853-0326", "description = TRANSISTOR PNP SI ... FT-50MHZ" The p/n 1853-0326 cross references to a Motorola MPS-U51. The MPS-U51 data sheet matches the part that fails so I'm sure I got a correct cross ref. I took a photo of the dead transistor. It is on .1" perf board for scale. You can read the "3-326" p/n and see the Motorola "M" logo. http://www.dropbox.com/gallery/28915695/1/HP5328A?h=da35c1 I look up the spec in the mps-u51 and see it is a to-220 like case and can handle 1W. I'm really surprised it burned out as I doubt an LED requires 1W even if showing an "8". Reading the mps-u51 spec sheet I see it has a low saturation voltage. Maybe that is why the selected it as it is being driven by 7400 TTL logic that goes through a connector and has some resistors involved. Question: These seem to be hardtop find. Can anyone suggest a good sub" Thanks, Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
