content/hp8662a_2.rst

Tue, 28 Aug 2018 15:05:01 +0200

author
David Douard <david.douard@logilab.fr>
date
Tue, 28 Aug 2018 15:05:01 +0200
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1 ===============================================
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2 HP8662A Synthetized Signal Generator - Part 2
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3 ===============================================
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4
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5 :Author: David Douard
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6 :Category: Electronics
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7 :Tags: HP8662A, repair, test equipment, HP, Generator, RF
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8 :series: HP 8662A
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9 :series_index: 2
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10
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11 This is the part 2 on my series about my HP 8662A Signal Generator.
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12 After fixing the PSU, several more problems needed to be addressed:
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13
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14 - a few sloppy keys on the keypad,
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15 - the know did not work at all,
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16 - and more importantly, some very unpleasant spectrums at some frequencies
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17 (covered in `part 3 <{filename}hp8662a_3.rst>`_),
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18 - some output level accuracy problems.
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20
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21 Keypad
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22 ======
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23
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24 The keypad was, as allways with HP devices from this period, very hard and
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25 "clunky" for most keys but 2.
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26
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27 No surprise: these keys were missing their famous (well, for some at least) spring:
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28
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29 .. image:: {filename}images/hp8662a/key_missing_springs.jpg
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30 :class: image-process-large-photo
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31
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32 As you can (not) see, the "Status" key as well as the "Increment Set" key have
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33 no spring at all.
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34
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35 While I was cleaning the unit, I've been half-lucky and found one of the 2
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36 missing springs. But I had to figure a solution for the other missing one.
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37
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38 I thought about:
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39
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40 - buying a replacement key: the ones I found are ridiculously expensite,
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41 - buying a front panel for an HP gear from this era: might be a reasonable approach,
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42 - looking for ready made springs: could not find,
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43 - asking some custom made ones from a company making springs: got a few
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44 responses, one of them quite reasonable even for small quantities (between 3
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45 to 5€ each).
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46
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47 While I was looking for a solution, I also gave a try to a simple solution: cut
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48 a replacement "spring" from a plastic wrap. I tried several wraps (of several
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49 widths), and I found one that seems to work just fine, and the feeling is about
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50 the same as original keys:
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51
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52 .. image:: {filename}images/hp8662a/key_hack.jpeg
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53 :class: image-process-large-photo
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54
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55 .. image:: {filename}images/hp8662a/key_hack_anim.gif
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56
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57 I cleaned all keys using some deoxit contact cleaner which also lubricated
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58 those noisy springs making the keys nice ans smooth again.
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60
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61 Rotary encoder
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62 ==============
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63
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64 The rotary encoder was not working at all, and once again, a classical failure
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65 for those old HP gears: the small bulb used as light source for the optical
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66 encoder was dead.
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67
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68 I tried to replace it with a 3mm LED I had in my junk box, but it did not work,
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69 so I bought a few replacement bulbs on ebay, and sure enough, the encoder is
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70 now working ok (not perfectly, there are some missed steps: there are two small
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71 screws that look like adjustment screws, but I'm not sure how to tune them).
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72
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73 .. image:: {filename}images/hp8662a/encoder.jpeg
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74 :class: image-process-large-photo

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