comparison: content/hp8662a.rst
content/hp8662a.rst
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| 42 before even attempting to fix the PSU. | 42 before even attempting to fix the PSU. |
| 43 | 43 |
| 44 | 44 |
| 45 .. image:: {static}/images/hp8662a/dirty_hp.jpg | 45 .. image:: {static}/images/hp8662a/dirty_hp.jpg |
| 46 :class: image-process-large-photo | 46 :class: image-process-large-photo |
| 47 :alt: Very dirty inside view of the HP8662A | |
| 47 | 48 |
| 48 | 49 |
| 49 And I must say that if most of the unit is very easy to service due to the | 50 And I must say that if most of the unit is very easy to service due to the |
| 50 modular design of all RF modules, making is very easy to remove all the boards | 51 modular design of all RF modules, making is very easy to remove all the boards |
| 51 and modules, there are also many parts that are connected together with wires | 52 and modules, there are also many parts that are connected together with wires |
| 52 soldered point to point, which makes disassembling the case, motherboards and | 53 soldered point to point, which makes disassembling the case, motherboards and |
| 53 so very tedious. | 54 so very tedious. |
| 54 | 55 |
| 55 .. image:: {static}/images/hp8662a/top_before_2.jpg | 56 .. image:: {static}/images/hp8662a/top_before_2.jpg |
| 56 :class: image-process-large-photo | 57 :class: image-process-large-photo |
| 58 :alt: Top view of the inside of the HP8662A | |
| 57 | 59 |
| 58 .. image:: {static}/images/hp8662a/bottom_before.jpg | 60 .. image:: {static}/images/hp8662a/bottom_before.jpg |
| 59 :class: image-process-large-photo | 61 :class: image-process-large-photo |
| 62 :alt: Bottom view of the inside of the HP8662A | |
| 60 | 63 |
| 61 .. image:: {static}/images/hp8662a/front_after.jpg | 64 .. image:: {static}/images/hp8662a/front_after.jpg |
| 62 :class: image-process-large-photo | 65 :class: image-process-large-photo |
| 66 :alt: Fromt view of the inside of the HP8662A | |
| 63 | 67 |
| 64 Also, there are hundreds of screws in this unit! it's insane. | 68 Also, there are hundreds of screws in this unit! it's insane. |
| 65 | 69 |
| 66 .. image:: {static}/images/hp8662a/top_after.jpg | 70 .. image:: {static}/images/hp8662a/top_after.jpg |
| 67 :class: image-process-large-photo | 71 :class: image-process-large-photo |
| 72 :alt: Top view of the many shielded compartments of the HP8662A | |
| 68 | 73 |
| 69 Whatever, I finally got to a point I could clean most of the parts of the unit, | 74 Whatever, I finally got to a point I could clean most of the parts of the unit, |
| 70 so I started to reassemble it. Unfortunately, I did not took enough pictures | 75 so I started to reassemble it. Unfortunately, I did not took enough pictures |
| 71 while the disassembling, so it took me some effort to have something that looks | 76 while the disassembling, so it took me some effort to have something that looks |
| 72 like an HP 8662A... | 77 like an HP 8662A... |
| 73 | 78 |
| 74 .. image:: {static}/images/hp8662a/reassembling_2.jpg | 79 .. image:: {static}/images/hp8662a/reassembling_2.jpg |
| 75 :class: image-process-large-photo | 80 :class: image-process-large-photo |
| 76 | 81 :alt: General view of the HP8662A case |
| 77 Once I had the structure of the generator back togother, with the back plane in | 82 |
| 83 Once I had the structure of the generator back together, with the back plane in | |
| 78 place but no other board nor module plugged in, I started to take care of the | 84 place but no other board nor module plugged in, I started to take care of the |
| 79 PSU. | 85 PSU. |
| 80 | 86 |
| 81 .. image:: {static}/images/hp8662a/reassembling_1.jpg | 87 .. image:: {static}/images/hp8662a/reassembling_1.jpg |
| 82 :class: image-process-large-photo | 88 :class: image-process-large-photo |
| 89 :alt: General view of the bottom of the HP8662A case with the main mother board | |
| 83 | 90 |
| 84 The PSU | 91 The PSU |
| 85 ======= | 92 ======= |
| 86 | 93 |
| 87 As I said, the first attempt to plug (and not even power on) the unit ended | 94 As I said, the first attempt to plug (and not even power on) the unit ended |
| 94 - The main switching power supply. The high voltage section is allways on, and | 101 - The main switching power supply. The high voltage section is allways on, and |
| 95 the mani switch on the front panel only activate the switching. | 102 the mani switch on the front panel only activate the switching. |
| 96 | 103 |
| 97 .. image:: {static}/images/hp8662a/PSU_simplified_schematic.jpeg | 104 .. image:: {static}/images/hp8662a/PSU_simplified_schematic.jpeg |
| 98 :class: image-process-large-photo | 105 :class: image-process-large-photo |
| 106 :alt: Simplified schematics of the HP8662A PSU | |
| 99 | 107 |
| 100 The 4 boards the PSU is made of are: | 108 The 4 boards the PSU is made of are: |
| 101 | 109 |
| 102 - a main board (A7A4) on which are the first stages of the AC rectification and | 110 - a main board (A7A4) on which are the first stages of the AC rectification and |
| 103 filtering, | 111 filtering, |
| 114 - a daughter board (A7A2) with the switching control circuit. The switching | 122 - a daughter board (A7A2) with the switching control circuit. The switching |
| 115 regulation being made on the 5.2V rail, which is not regulated by A7A1. | 123 regulation being made on the 5.2V rail, which is not regulated by A7A1. |
| 116 | 124 |
| 117 .. image:: {static}/images/hp8662a/PSU_block_diagram.jpeg | 125 .. image:: {static}/images/hp8662a/PSU_block_diagram.jpeg |
| 118 :class: image-process-large-photo | 126 :class: image-process-large-photo |
| 127 :alt: Block diagram of the HP8662A PSU | |
| 119 | 128 |
| 120 So I gave a close look at thes boards, beginning by the main board, the I found | 129 So I gave a close look at thes boards, beginning by the main board, the I found |
| 121 the culprit for the smoke: the input protection thermistor. Strangely, it still | 130 the culprit for the smoke: the input protection thermistor. Strangely, it still |
| 122 measures a decent resistance value, but hey. | 131 measures a decent resistance value, but hey. |
| 123 | 132 |
| 126 junk parts; only a slighty highter value one (a XXX, which is more like | 135 junk parts; only a slighty highter value one (a XXX, which is more like |
| 127 20Ω @25°C). Not ideal, but for now, it seems to work fine. | 136 20Ω @25°C). Not ideal, but for now, it seems to work fine. |
| 128 | 137 |
| 129 .. image:: {static}/images/hp8662a/smoking_thermistor.jpg | 138 .. image:: {static}/images/hp8662a/smoking_thermistor.jpg |
| 130 :class: image-process-large-photo | 139 :class: image-process-large-photo |
| 140 :alt: Picture of the smoked thermistor | |
| 131 | 141 |
| 132 After this first step forward, I was not confident enought to plug the boards | 142 After this first step forward, I was not confident enought to plug the boards |
| 133 back in place and try again (I am always worried when I repair switching | 143 back in place and try again (I am always worried when I repair switching |
| 134 PSUs... they can fail in flame and glory sometimes). So I checked all the | 144 PSUs... they can fail in flame and glory sometimes). So I checked all the |
| 135 diodes and transistors of the PSU, but none looked short. | 145 diodes and transistors of the PSU, but none looked short. |
| 147 did not stay on, and the error LED did turn on. All the voltages produced by | 157 did not stay on, and the error LED did turn on. All the voltages produced by |
| 148 the inverter board were very low. Somethin was wrong. | 158 the inverter board were very low. Somethin was wrong. |
| 149 | 159 |
| 150 .. image:: {static}/images/hp8662a/PSU_inverter_schematic.jpeg | 160 .. image:: {static}/images/hp8662a/PSU_inverter_schematic.jpeg |
| 151 :class: image-process-large-photo | 161 :class: image-process-large-photo |
| 162 :alt: Full schematic of the PSU | |
| 152 | 163 |
| 153 Looking at the schematics and the boards, I did find several failure points: | 164 Looking at the schematics and the boards, I did find several failure points: |
| 154 | 165 |
| 155 - one of the 2 150µH inductors on the 160VDC rails (L6 anf L7 on A7A3) ) looked | 166 - one of the 2 150µH inductors on the 160VDC rails (L6 anf L7 on A7A3) ) looked |
| 156 a bit odd to me: it was not sitting flat on the PCB, which it should for this | 167 a bit odd to me: it was not sitting flat on the PCB, which it should for this |
| 161 more parts than I really need, when these are cheap, just in case; seems to | 172 more parts than I really need, when these are cheap, just in case; seems to |
| 162 be a good idea), | 173 be a good idea), |
| 163 | 174 |
| 164 .. image:: {static}/images/hp8662a/broken_choke.jpg | 175 .. image:: {static}/images/hp8662a/broken_choke.jpg |
| 165 :class: image-process-large-photo | 176 :class: image-process-large-photo |
| 177 :alt: Pictures of broken choke coils | |
| 166 | 178 |
| 167 .. image:: {static}/images/hp8662a/replacement_choke.jpg | 179 .. image:: {static}/images/hp8662a/replacement_choke.jpg |
| 168 :class: image-process-large-photo | 180 :class: image-process-large-photo |
| 181 :alt: Picture of the replacement choke coils | |
| 169 | 182 |
| 170 - there are 2 small 400mA fuses on the inverter board to protect the base of | 183 - there are 2 small 400mA fuses on the inverter board to protect the base of |
| 171 the 2 switching (bipolar!) transistors (first time I see the base of an NPN | 184 the 2 switching (bipolar!) transistors (first time I see the base of an NPN |
| 172 transistor protected by a fuse, but it's also the first time I repair a | 185 transistor protected by a fuse, but it's also the first time I repair a |
| 173 switching PSU which the main switching transistors are bipolar ones and not | 186 switching PSU which the main switching transistors are bipolar ones and not |
| 176 each. So for now, I've replaced it with a simple 5x20 glass fuse: not as | 189 each. So for now, I've replaced it with a simple 5x20 glass fuse: not as |
| 177 skookum but does the job for a few cents. | 190 skookum but does the job for a few cents. |
| 178 | 191 |
| 179 .. image:: {static}/images/hp8662a/fuse_replacement.jpeg | 192 .. image:: {static}/images/hp8662a/fuse_replacement.jpeg |
| 180 :class: image-process-large-photo | 193 :class: image-process-large-photo |
| 194 :alt: Picture of the hacked replacement fuse | |
| 181 | 195 |
| 182 | 196 |
| 183 After these fixes, I reassembled the PSU and tried again: the result was quite | 197 After these fixes, I reassembled the PSU and tried again: the result was quite |
| 184 promising, but not a complete success: the PSU seemed to start, but very | 198 promising, but not a complete success: the PSU seemed to start, but very |
| 185 quickly stops itself with an error LED on: the overvoltage protection was | 199 quickly stops itself with an error LED on: the overvoltage protection was |
