[time-nuts] HP5328A LEDS driver transistor

David davidwhess at gmail.com
Sun Jan 22 15:59:57 EST 2012

The package is a TO-202 with the tab cut off or at least the MPS-U51
uses a TO-202 package.  Be careful when you replace it because the
pinout is EBC which is deprecated in power transistor packages.

Ic = 2.0 A
Vceo = 30 V
Pd = 1 W @ Ta 25 C
hfe = 60 @ 0.1 A
Ft = 50 MHz min

This is a very non-critical application.  I agree with Brooke Clarke
that a 2N4403 will probably work fine.  If you want something closer
then there are any number of TO-126 and TO-225 transistors like the
MJE170 which will work but again, be careful of the pinout.

On Sun, 22 Jan 2012 10:41:23 -0800, Chris Albertson
<albertson.chris at gmail.com> wrote:

>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.
>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"

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