Re: HP 140B LVPS -12.6V Not Working
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According to the HEWLETT PACKARD TRANSISTORS & DIODES.? COMMERCIAL CROSS-REFERENCE, an 1854-0071 crosses to a 2N3704 or a 2N3391.? Both of those are ECB (apologies to David if those were ones you'd already mentioned).? No wonder things haven't made sense to me.? At least the dots seem to coincide with the emitter as I was thinking.? Now I have more checking to do...
Thanks, Barry - N4BUQ
From: "n4buq" <n4buq@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Monday, April 22, 2024 6:43:15 PM
Subject: Re: [HP-Agilent-Keysight-equipment] HP 140B LVPS -12.6V Not Working
I've been cross-checking the board against the schematic.? I thought I had the dot convention correct (emitter) but then the differences between a few of the transistors on the board made me realize something didn't match so I need to be even more careful if I end up needing to replace those. I'm just glad wires don't have dots. Thanks,
Barry - N4BUQ I would've guessed that the dot marks the collector. At least that
was the convention used on all the parts I encountered as a kid. The
literature of the day often referred to "the collector dot". But of
course that doesn't mean that other companies/countries followed
that convention, so I'm curious: Are you just guessing (say, based
on a quick DMM diode check, in which case you're rolling the dice),
or did you cross-check with some circuit-tracing against a
schematic?
And if you're talking about a TO-92, there is no standard pinout.
Parts of US design generally follow EBC, UK parts often follow CBE
(making it easy to swap with US parts by simply installing the other
way around), Japanese parts are frequently BEC (I've also
encountered ECB), but "generally" does mean "not always" here. You
have to check, don't assume.
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070
On 4/22/2024 3:38 PM, n4buq wrote:
Something about this is confusing
me.? Looking at the board, the transistors and diodes all have
a dot at one lead.? I was thinking that dot indicated the
emitter and for some transistors, that holds.? It agrees with
the 2n3409 I replaced and most of the metal-hat transistors.?
With the flat of the 2n3904's TO92 facing me, left to right is
EBC.? For Q484, though, the diode across BE (I can't read it
very well but I think that's CR485 or CR486) is connected to
the center lead and the right-hand lead (facing the
transistor's flat).? Do those not follow the same convention
as, say, a 2n3904?? I'm used to either EBC being left-to-right
facing the flat or, possibly, B on the left or right, but this
is puzzling to me.
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