Author Topic: Component ID help on an Agilent power-supply board  (Read 230 times)

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Offline mark03

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Component ID help on an Agilent power-supply board
« on: March 12, 2019, 03:58:11 pm »
I'm trying to work out the schematic of a defective "A50 DC-DC converter" board in an Agilent 4396B.  Mostly it's smooth sailing, but there are a couple of SOT-23 parts I can't find referenced in any of the SMD-markings lists returned by google. In the image below (shot through my microscope eyepiece---apologies for the less-than-ideal illumination), I believe the Y27 and Z49, at center-right, are single zener diodes in SOT-23 packages. 

I can't ID the SOT-23 next to the zener diodes, which may be marked "B3" except that it is a very stylized font so I'm not sure if that's what the marking actually is.

I'm also trying to ID the two SOT-23's at the top, marked C3.  These are quite common on this board and I think they're transistors of some kind but haven't been able to work out which one.

At the left edge, is there anything besides a capacitor that the 221J could be?  It's quite a brilliant blue, quite tall, very distinctive.  No other capacitors on the board like it.  And I'm measuring ~ 8 ohms across it.

This section of the board implements the auto shutdown for over-current and fan not rotating conditions.  The 74AC00 is wired as a flip flop plus a couple of gates.  Another weird thing in this photo, the ferrite inductors at the bottom (there are four of them in total, SO-8 pinout, but only two pins connected) appear to be connected in parallel.

The board was designed in Japan in the late 90s, if that helps.
« Last Edit: March 12, 2019, 04:04:25 pm by mark03 »

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