M
Michael Kers
Guest
Hi,
Preamble
=====
A little project of mine is to fix an older HP 6284A power supply. I
have the schematics for it, and am working through part-by-part
looking for anything defective. I came across something that has me
stumped. The power supply was used surplus, and did not work (since
I've had it)
Questions:
======
1) For a transistor BE 0.812V seems out of spec, could this be
something other than a bipolar junction silicon device?
2) What manufacturer might have made this device?
Background
=======
This power supply has a display, and in the display driver circuit
there is a dual-transistor to-78 package device (metal can, 6 leads, 2
matched transistors).
According to the schematics, there should be an Agilent 1854-0229
(Analog Devices MAT02FH, dual BJT, silicon, NPN, diff amp). I have 2
of these agilent parts (the mystery meat should be the third part,
identical to the other two, but its not), and the BE breakdown voltage
is around 0.65V for both sides of both known devices. This oddball
device has a breakdown of 0.812V or so.
I'm measuring the 0.812V with a fluke multimeter that has a diode
testing tool on it.
The oddball has the markings K8721 4-221 on it, and 2 symbols: an
lower case "i" (clear) in box of black background, and a delta symbol
(see attachment). I've tried every cross-reference I can (NEC, NTE,
ECG, Fairchild, intersil, google) but this part doesn't seem to exist
(?!?).
Thanks,
Mike
Preamble
=====
A little project of mine is to fix an older HP 6284A power supply. I
have the schematics for it, and am working through part-by-part
looking for anything defective. I came across something that has me
stumped. The power supply was used surplus, and did not work (since
I've had it)
Questions:
======
1) For a transistor BE 0.812V seems out of spec, could this be
something other than a bipolar junction silicon device?
2) What manufacturer might have made this device?
Background
=======
This power supply has a display, and in the display driver circuit
there is a dual-transistor to-78 package device (metal can, 6 leads, 2
matched transistors).
According to the schematics, there should be an Agilent 1854-0229
(Analog Devices MAT02FH, dual BJT, silicon, NPN, diff amp). I have 2
of these agilent parts (the mystery meat should be the third part,
identical to the other two, but its not), and the BE breakdown voltage
is around 0.65V for both sides of both known devices. This oddball
device has a breakdown of 0.812V or so.
I'm measuring the 0.812V with a fluke multimeter that has a diode
testing tool on it.
The oddball has the markings K8721 4-221 on it, and 2 symbols: an
lower case "i" (clear) in box of black background, and a delta symbol
(see attachment). I've tried every cross-reference I can (NEC, NTE,
ECG, Fairchild, intersil, google) but this part doesn't seem to exist
(?!?).
Thanks,
Mike