[time-nuts] HP5328A LEDS driver transistor
rlajeunesse at sbcglobal.net
Sun Jan 22 18:18:56 EST 2012
Specifying the digit scan transistor is a bit tricky, and often power
dissipation is just not a concern. Why? Consider the duty cycle. A transistor
switching one amp (a LOT for 7+1 segments) with a 0.6V saturation dissipates
600mW, but only when on. Given a 1/8 duty cycle that's 75mW average. Any stinkin
TO-92 will handle that power all day long! Only an ultra-conservative design
would use an exposed tab transistor, as expected for HP!
Trust me, I put over 20,000 "digit" drive transistors to work in Terminal One
O'Hare. Non-Darlington TO-220 parts switching 6A each at 1/16 duty, mounted with
a plastic rivit to nothing more than a small foil pad on 2-sided FR-4 PCB.
Dissipation was less than 200mW apiece. Still working last I knew, after some 25
years. FWIW it was the LEDs that needed cooling, especially with 19,000 LEDs in
one baggage claim sign.
From: Chris Albertson <albertson.chris at gmail.com>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
Sent: Sun, January 22, 2012 5:40:50 PM
Subject: Re: [time-nuts] HP5328A LEDS driver transistor
Thanks everyone for all the options. OK there are real MPS-U51 for $5
or $6 each. The NTE parts sells for between $25 and $30. HP places
these just on top of each digit with the tap fasting the plastic LED
so it can't short. HP also cuts the taps so they can't short to the
case. I think they grossly per spec'd them because they are used in a
place where there is no heat sink and very little airflow. I say
"over spec" but yet two burn out.
Funny the seller thought the counter worked. The burned out digits
were the least significant and with them out you still have a 7
digital counter. Really all that most people need for aligning radios
My plan now is to do a parametric search on Digikey/Mouser a quick
search found many for under $1 that could work. I'll wait 'till I'm
in need of some parts to build my next projects and add a few
On Sun, Jan 22, 2012 at 1:07 PM, Stan Searing <timenutstan at gmail.com> wrote:
> on my shelf I'd sell for $50 if you are ever up in San Jose).
If you could drop them at Cal State I might take you up on that.
Yes, I'll look at that transistor below
> I'd use a
> DigiKey (but as mentioned by others,
> watch the pinout, as most any power tab transistor will have the collector
> in the center,
> while the MPS-U51 is one of the few exceptions). You might also need to
> slim down
> the leads to fit the PC board.
> On Sun, Jan 22, 2012 at 12:34 PM, Don Latham <djl at montana.com> wrote:
>> NTE lists their equivalent as: NTE-189 See:
>> Newark has 262 of them :-)
>> Chris Albertson
>> > 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
>> > _______________________________________________
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>> "Neither the voice of authority nor the weight of reason and argument
>> are as significant as experiment, for thence comes quiet to the mind."
>> R. Bacon
>> "If you don't know what it is, don't poke it."
>> Ghost in the Shell
>> Dr. Don Latham AJ7LL
>> Six Mile Systems LLP
>> 17850 Six Mile Road
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>> Huson, MT, 59846
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