[time-nuts] HP5328A LEDS driver transistor
albertson.chris at gmail.com
Sun Jan 22 13:41:23 EST 2012
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
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.
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"
Redondo Beach, California
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