content/hp8904a_2.rst

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14 schematic of this later A2 board (as it is referenced in the servce 14 schematic of this later A2 board (as it is referenced in the servce
15 manual) is notavailable in any available HP's manual... 15 manual) is notavailable in any available HP's manual...
16 16
17 The board I have is the second revision: 17 The board I have is the second revision:
18 18
19 .. image:: {filename}images/hp8904a/A2_top.jpg 19 .. image:: {static}images/hp8904a/A2_top.jpg
20 :alt: The logic board (A2) of the HP8904A signal generator. 20 :alt: The logic board (A2) of the HP8904A signal generator.
21 21
22 And the bottom side of the PCB: 22 And the bottom side of the PCB:
23 23
24 .. image:: {filename}images/hp8904a/A2_bottom.jpg 24 .. image:: {static}images/hp8904a/A2_bottom.jpg
25 :alt: Bottom side of the A2 board. 25 :alt: Bottom side of the A2 board.
26 26
27 According to the presence of soldering flux, it looks like the U46 27 According to the presence of soldering flux, it looks like the U46
28 chip (a 74ALS73CN) on this board has been replaced: 28 chip (a 74ALS73CN) on this board has been replaced:
29 29
30 .. image:: {filename}images/hp8904a/A2_U46.jpg 30 .. image:: {static}images/hp8904a/A2_U46.jpg
31 :alt: The U46 chip seems to have been replaced. 31 :alt: The U46 chip seems to have been replaced.
32 32
33 After having moved my scope probe around the 10MHz output (J102), I've 33 After having moved my scope probe around the 10MHz output (J102), I've
34 found that the most probable culprit is the Q106 transistor (which 34 found that the most probable culprit is the Q106 transistor (which
35 seems to be a bipolar one). The 10MHz arrives to the base signal, the 35 seems to be a bipolar one). The 10MHz arrives to the base signal, the
41 41
42 The problem was then to identify a reasonable replacement part for 42 The problem was then to identify a reasonable replacement part for
43 this puppy. It presents itself as a Motorola with weird reference 43 this puppy. It presents itself as a Motorola with weird reference
44 ``3 0659``: 44 ``3 0659``:
45 45
46 .. image:: {filename}images/hp8904a/HP8904A_Q106.jpg 46 .. image:: {static}images/hp8904a/HP8904A_Q106.jpg
47 :alt: The failing transistor. 47 :alt: The failing transistor.
48 48
49 Having no luck searching the net, I've asked the `wonderful EEVBlog 49 Having no luck searching the net, I've asked the `wonderful EEVBlog
50 community`_ for some help identifying this transistor. My question 50 community`_ for some help identifying this transistor. My question
51 obviously was answered very quickly by several fellows. First I've had 51 obviously was answered very quickly by several fellows. First I've had
60 broken leg of the transistor, and bingo, the 10MHz output is working 60 broken leg of the transistor, and bingo, the 10MHz output is working
61 again! 61 again!
62 62
63 This EEVBlog community really is awesome! 63 This EEVBlog community really is awesome!
64 64
65 .. _`fixed the PSU of one of my HP8904A`: {filename}/hp8904a.rst 65 .. _`fixed the PSU of one of my HP8904A`: {static}/hp8904a.rst
66 .. _`wonderful EEVBlog community`: http://www.eevblog.com/forum/repair/repair-of-an-hp8904a-signal-generator 66 .. _`wonderful EEVBlog community`: http://www.eevblog.com/forum/repair/repair-of-an-hp8904a-signal-generator
67 67
68 68

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