comparison: content/hp34970a.rst
content/hp34970a.rst
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| 12 I recently "scored" a HP 34970A with the DMM included and 2 plugin | 12 I recently "scored" a HP 34970A with the DMM included and 2 plugin |
| 13 cards (HP 34901A and HP 34907A) for less than 200€. The plugins should | 13 cards (HP 34901A and HP 34907A) for less than 200€. The plugins should |
| 14 be in working condition, but the main switch unit was almost "given" | 14 be in working condition, but the main switch unit was almost "given" |
| 15 with the plugin modules since it is non functional. | 15 with the plugin modules since it is non functional. |
| 16 | 16 |
| 17 .. image:: {filename}/images/hp34970a/front-view.jpg | 17 .. image:: {static}/images/hp34970a/front-view.jpg |
| 18 :alt: front view of the HP 34970A data acquisition unit | 18 :alt: front view of the HP 34970A data acquisition unit |
| 19 | 19 |
| 20 It's in very good shape, the front panel and the push buttons are | 20 It's in very good shape, the front panel and the push buttons are |
| 21 clean. The knob is nice but it has a rough step when turning it for a | 21 clean. The knob is nice but it has a rough step when turning it for a |
| 22 complete revolution. | 22 complete revolution. |
| 35 - the main logic/cpu board on the bottom left side, | 35 - the main logic/cpu board on the bottom left side, |
| 36 - the DMM module, juste above the main board, | 36 - the DMM module, juste above the main board, |
| 37 - the frontpanel and | 37 - the frontpanel and |
| 38 - the back plane where plugin modules are connected. | 38 - the back plane where plugin modules are connected. |
| 39 | 39 |
| 40 .. image:: {filename}/images/hp34970a/bottom-view.jpg | 40 .. image:: {static}/images/hp34970a/bottom-view.jpg |
| 41 :alt: bottom view of the HP 34970A | 41 :alt: bottom view of the HP 34970A |
| 42 | 42 |
| 43 .. image:: {filename}/images/hp34970a/top-view.jpg | 43 .. image:: {static}/images/hp34970a/top-view.jpg |
| 44 :alt: top view of the HP 34970A with DMM removed | 44 :alt: top view of the HP 34970A with DMM removed |
| 45 | 45 |
| 46 .. image:: {filename}/images/hp34970a/dmm.jpg | 46 .. image:: {static}/images/hp34970a/dmm.jpg |
| 47 :alt: DMM module of the HP 34970A | 47 :alt: DMM module of the HP 34970A |
| 48 | 48 |
| 49 The front panel hold the keyboard, the rotary encoder and the diplay system. | 49 The front panel hold the keyboard, the rotary encoder and the diplay system. |
| 50 | 50 |
| 51 .. image:: {filename}/images/hp34970a/front-panel.jpg | 51 .. image:: {static}/images/hp34970a/front-panel.jpg |
| 52 :alt: front panel of the HP 34970A | 52 :alt: front panel of the HP 34970A |
| 53 | 53 |
| 54 The front panel is managed by a 80C51 (a 87C51 actually) | 54 The front panel is managed by a 80C51 (a 87C51 actually) |
| 55 microcontroller. It's responsible for handling the keyboard and | 55 microcontroller. It's responsible for handling the keyboard and |
| 56 feeding the shift registers of the VFD drivers (a pair of | 56 feeding the shift registers of the VFD drivers (a pair of |
| 57 HV518PJ). The communication with the main CPU is a serial line with | 57 HV518PJ). The communication with the main CPU is a serial line with |
| 58 opamps to adjust the signal levels. | 58 opamps to adjust the signal levels. |
| 59 | 59 |
| 60 The chips are PLCC44 located under the VFD are the drivers: | 60 The chips are PLCC44 located under the VFD are the drivers: |
| 61 | 61 |
| 62 .. image:: {filename}/images/hp34970a/front-panel-pcb.jpg | 62 .. image:: {static}/images/hp34970a/front-panel-pcb.jpg |
| 63 :alt: front panel PCB of the HP 34970A | 63 :alt: front panel PCB of the HP 34970A |
| 64 | 64 |
| 65 On my unit, the voltage levels for the VFD are fine. I suspected that | 65 On my unit, the voltage levels for the VFD are fine. I suspected that |
| 66 one of the 2 VFD drivers (the one responsible for driving the grids) | 66 one of the 2 VFD drivers (the one responsible for driving the grids) |
| 67 were partially failing, so I ordered a pair of new drivers, as well as | 67 were partially failing, so I ordered a pair of new drivers, as well as |
| 85 | 85 |
| 86 The tricky part of installing these PLCC sockets is that decoupling | 86 The tricky part of installing these PLCC sockets is that decoupling |
| 87 capacitors (C6, C7, C9 and C10) are a bit too close, so I had to move | 87 capacitors (C6, C7, C9 and C10) are a bit too close, so I had to move |
| 88 them. | 88 them. |
| 89 | 89 |
| 90 .. image:: {filename}/images/hp34970a/front-panel-sockets.jpg | 90 .. image:: {static}/images/hp34970a/front-panel-sockets.jpg |
| 91 :alt: PLCC sockets for the VFD drivers of the HP 34970A | 91 :alt: PLCC sockets for the VFD drivers of the HP 34970A |
| 92 | 92 |
| 93 | 93 |
| 94 Now I had to try to rejuvenate the tungsten filaments. Like for old | 94 Now I had to try to rejuvenate the tungsten filaments. Like for old |
| 95 CRT (and even for triodes), the filament, which is responsible for | 95 CRT (and even for triodes), the filament, which is responsible for |
| 97 polluted and loose their emissive power. A common trick to "clean" | 97 polluted and loose their emissive power. A common trick to "clean" |
| 98 them is to apply a much higher voltage than rated so they shine for a | 98 them is to apply a much higher voltage than rated so they shine for a |
| 99 few seconds. One mst be careful not to burn them, otherwise the VFD is | 99 few seconds. One mst be careful not to burn them, otherwise the VFD is |
| 100 definitively lost. | 100 definitively lost. |
| 101 | 101 |
| 102 .. image:: {filename}/images/hp34970a/vfd-back.jpg | 102 .. image:: {static}/images/hp34970a/vfd-back.jpg |
| 103 :alt: back side of the VFD (probably dead) module | 103 :alt: back side of the VFD (probably dead) module |
| 104 | 104 |
| 105 So I tried such a rejuvenation on my VFD module. I wasn't sure what | 105 So I tried such a rejuvenation on my VFD module. I wasn't sure what |
| 106 color the filaments must be heated to (between a light orange to an | 106 color the filaments must be heated to (between a light orange to an |
| 107 almost white yellow). I was doing this using my `Lambda PSU | 107 almost white yellow). I was doing this using my `Lambda PSU |
| 108 <{filename}/LPD422FM.rst>`_ raising the voltage while looking at the | 108 <{static}/LPD422FM.rst>`_ raising the voltage while looking at the |
| 109 filaments. | 109 filaments. |
| 110 | 110 |
| 111 The results are very disappointing. The VFD is a little bit brighter, | 111 The results are very disappointing. The VFD is a little bit brighter, |
| 112 but the spilling over between digits is now much worse... | 112 but the spilling over between digits is now much worse... |
| 113 | 113 |
