comparison: content/hp8904a.rst
content/hp8904a.rst
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| 14 (bought them on ebay around 2007 IIRC). One of them is working | 14 (bought them on ebay around 2007 IIRC). One of them is working |
| 15 properly, but the second one had very inaccurate output levels, | 15 properly, but the second one had very inaccurate output levels, |
| 16 generating a non-symmetric signal when output level was set above 5V | 16 generating a non-symmetric signal when output level was set above 5V |
| 17 or something like that. | 17 or something like that. |
| 18 | 18 |
| 19 .. image:: {filename}images/hp8904a/twin_HP8904A.jpg | 19 .. image:: {static}images/hp8904a/twin_HP8904A.jpg |
| 20 :alt: My 2 HP8904A synthetizers. | 20 :alt: My 2 HP8904A synthetizers. |
| 21 | 21 |
| 22 I knew for a fact that the PSU was the problem (thanks to the fact I | 22 I knew for a fact that the PSU was the problem (thanks to the fact I |
| 23 have 2 units, I could easily swap elements between the units). Back | 23 have 2 units, I could easily swap elements between the units). Back |
| 24 then, I spent a bit of time trying to figure out what was going wrong, | 24 then, I spent a bit of time trying to figure out what was going wrong, |
| 30 | 30 |
| 31 | 31 |
| 32 The PSU Problem | 32 The PSU Problem |
| 33 =============== | 33 =============== |
| 34 | 34 |
| 35 .. image:: {filename}images/hp8904a/hp8904a_top.jpg | 35 .. image:: {static}images/hp8904a/hp8904a_top.jpg |
| 36 :alt: Top view of the HP8904A | 36 :alt: Top view of the HP8904A |
| 37 | 37 |
| 38 The PSU board is the one at the rear of the unit, on the upper part of | 38 The PSU board is the one at the rear of the unit, on the upper part of |
| 39 the case (the lower part hold the analogic boards). The PSU is not a | 39 the case (the lower part hold the analogic boards). The PSU is not a |
| 40 custom HP board, but is a Computer Products switchmode supply (90 | 40 custom HP board, but is a Computer Products switchmode supply (90 |
| 71 | 71 |
| 72 In order to be able to follow the tracks, I had to remove the heat | 72 In order to be able to follow the tracks, I had to remove the heat |
| 73 sink and split these two boards apart, since it's not easy to deal | 73 sink and split these two boards apart, since it's not easy to deal |
| 74 with this: | 74 with this: |
| 75 | 75 |
| 76 .. image:: {filename}images/hp8904a/hp8904_psu_followme.jpg | 76 .. image:: {static}images/hp8904a/hp8904_psu_followme.jpg |
| 77 :alt: part of the +16.3V PSU rail | 77 :alt: part of the +16.3V PSU rail |
| 78 | 78 |
| 79 So I removed the heatsink and disassembled this small board from the | 79 So I removed the heatsink and disassembled this small board from the |
| 80 main one (which was quite painful, since I don't have a disoldering | 80 main one (which was quite painful, since I don't have a disoldering |
| 81 station. Disassembling the 3x 8 pins angle connectors from the double | 81 station. Disassembling the 3x 8 pins angle connectors from the double |
| 82 sided PCB was not a piece of cake...) | 82 sided PCB was not a piece of cake...) |
| 83 | 83 |
| 84 .. image:: {filename}images/hp8904a/HP8904A_daughter_board.jpg | 84 .. image:: {static}images/hp8904a/HP8904A_daughter_board.jpg |
| 85 :alt: the small daughter board of the PSU | 85 :alt: the small daughter board of the PSU |
| 86 | 86 |
| 87 After that, I noticed a possible leak of a small cap, but this was on | 87 After that, I noticed a possible leak of a small cap, but this was on |
| 88 the 5.1V rail. Should not be related to my +16.3V problem. | 88 the 5.1V rail. Should not be related to my +16.3V problem. |
| 89 | 89 |
| 96 After having replaced the caps, the PSU was still failing. So I really | 96 After having replaced the caps, the PSU was still failing. So I really |
| 97 had to understand the schematic to investigate more. | 97 had to understand the schematic to investigate more. |
| 98 | 98 |
| 99 The part of the schematic involved in the +16.3V rail is the following: | 99 The part of the schematic involved in the +16.3V rail is the following: |
| 100 | 100 |
| 101 .. image:: {filename}images/hp8904a/psu_schematic.png | 101 .. image:: {static}images/hp8904a/psu_schematic.png |
| 102 :alt: part of the schemtic of the PSU | 102 :alt: part of the schemtic of the PSU |
| 103 | 103 |
| 104 At first glance (the schematic was then a bunch of poorly made | 104 At first glance (the schematic was then a bunch of poorly made |
| 105 "Dave-CAD-like" sketches on several sheets), the exact role of the | 105 "Dave-CAD-like" sketches on several sheets), the exact role of the |
| 106 LM392 opamp was not clear to me, but when I redrew the schematic a bit | 106 LM392 opamp was not clear to me, but when I redrew the schematic a bit |
| 168 | 168 |
| 169 The procedure to restore the serial number can be found in the service | 169 The procedure to restore the serial number can be found in the service |
| 170 manual of the HP8904. | 170 manual of the HP8904. |
| 171 | 171 |
| 172 And in case of failed battery, the memory can be restored following | 172 And in case of failed battery, the memory can be restored following |
| 173 `this document <{filename}pdfs/HP_8904A_Service_Notes_2.pdf>`_ | 173 `this document <{static}pdfs/HP_8904A_Service_Notes_2.pdf>`_ |
| 174 | 174 |
| 175 .. _`thread pointing to an HP service document`: http://www.eevblog.com/forum/testgear/hp-8904a-options/ | 175 .. _`thread pointing to an HP service document`: http://www.eevblog.com/forum/testgear/hp-8904a-options/ |
| 176 | 176 |
| 177 | 177 |
| 178 Next steps | 178 Next steps |
