comparison: content/TeK2445_2.rst
content/TeK2445_2.rst
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| 114:33cd55d481ba | 115:6b6e13653348 |
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| 7 :Tags: Tektronics, 2445, analog scope, repair, test equipment | 7 :Tags: Tektronics, 2445, analog scope, repair, test equipment |
| 8 :series: Tek2445 PSU repair | 8 :series: Tek2445 PSU repair |
| 9 :series_index: 2 | 9 :series_index: 2 |
| 10 | 10 |
| 11 After a `quick repair of the PSU of my Tek 2445 | 11 After a `quick repair of the PSU of my Tek 2445 |
| 12 <{filename}/TeK2445.rst>`_, I've started a more systematic replacement | 12 <{static}/TeK2445.rst>`_, I've started a more systematic replacement |
| 13 of the capacitors. | 13 of the capacitors. |
| 14 | 14 |
| 15 .. image:: {filename}/images/tek2445/psu_caps_replaced.jpg | 15 .. image:: {static}/images/tek2445/psu_caps_replaced.jpg |
| 16 :alt: Tek2445 PSU Caps being replaced. | 16 :alt: Tek2445 PSU Caps being replaced. |
| 17 | 17 |
| 18 But I was also a bit worried because of a dirty noise coming from the | 18 But I was also a bit worried because of a dirty noise coming from the |
| 19 preregulator area. | 19 preregulator area. |
| 20 | 20 |
| 44 very hot as soon as the main oscillator starts up. A bit strange, | 44 very hot as soon as the main oscillator starts up. A bit strange, |
| 45 since the capacitor C1071 seems fine (I do not have a ESR meter, but | 45 since the capacitor C1071 seems fine (I do not have a ESR meter, but |
| 46 hey, there is no way higher ESR could lead to overcurrent flowing | 46 hey, there is no way higher ESR could lead to overcurrent flowing |
| 47 through this resistor). | 47 through this resistor). |
| 48 | 48 |
| 49 .. image:: {filename}/images/tek2445/psu_prereg.png | 49 .. image:: {static}/images/tek2445/psu_prereg.png |
| 50 :alt: Schematic of the preregulator of teh Tek2445 | 50 :alt: Schematic of the preregulator of teh Tek2445 |
| 51 | 51 |
| 52 But powering up and down the PSU again and again, with its freaking | 52 But powering up and down the PSU again and again, with its freaking |
| 53 and noisy switching problem, finally killed the MOSFET (IRF820) power | 53 and noisy switching problem, finally killed the MOSFET (IRF820) power |
| 54 transistors (Q1050, Q1060 and Q1070) producing flames. The plastic | 54 transistors (Q1050, Q1060 and Q1070) producing flames. The plastic |
| 55 protection on Q1060 directed all the heat directly on the poor LR1060 | 55 protection on Q1060 directed all the heat directly on the poor LR1060 |
| 56 which exploded as well... Which is a problem since I do not know the | 56 which exploded as well... Which is a problem since I do not know the |
| 57 exact specifications of the device; the service manual do not give the | 57 exact specifications of the device; the service manual do not give the |
| 58 value of the resistor in parallel with the 2.5µH inductance. | 58 value of the resistor in parallel with the 2.5µH inductance. |
| 59 | 59 |
| 60 .. image:: {filename}/images/tek2445/dead_transistors.jpg | 60 .. image:: {static}/images/tek2445/dead_transistors.jpg |
| 61 :alt: Q1050, 1060 and Q1070 are dead. | 61 :alt: Q1050, 1060 and Q1070 are dead. |
| 62 | 62 |
| 63 For now, I've picked up a 3W 100Ω resistor and I've made a self by | 63 For now, I've picked up a 3W 100Ω resistor and I've made a self by |
| 64 hand. As I don't have a RLC meter, I don't known its exact value so | 64 hand. As I don't have a RLC meter, I don't known its exact value so |
| 65 I've took a few measures of its impedance at several frequencies, and | 65 I've took a few measures of its impedance at several frequencies, and |
| 75 that worries me a bit is the much lower Rds value (0.4Ω versus 3Ω for | 75 that worries me a bit is the much lower Rds value (0.4Ω versus 3Ω for |
| 76 the IRF820). Means higher peak currents. Q1030 and R1052 also | 76 the IRF820). Means higher peak currents. Q1030 and R1052 also |
| 77 died. The transistor is a 2N3905 (which I don't have around either) so | 77 died. The transistor is a 2N3905 (which I don't have around either) so |
| 78 I've replaced it with a bigger TIP32C. | 78 I've replaced it with a bigger TIP32C. |
| 79 | 79 |
| 80 .. image:: {filename}/images/tek2445/beafier_transistors.jpg | 80 .. image:: {static}/images/tek2445/beafier_transistors.jpg |
| 81 :alt: Beafier replacement rtansistors, and a handmade coil. | 81 :alt: Beafier replacement rtansistors, and a handmade coil. |
| 82 | 82 |
| 83 From there, I began to check most of the components in this | 83 From there, I began to check most of the components in this |
| 84 preregulator part of the PSU before even attempting to apply power. | 84 preregulator part of the PSU before even attempting to apply power. |
| 85 | 85 |
| 87 of U1030), by powering it with my new old Lambda linear power | 87 of U1030), by powering it with my new old Lambda linear power |
| 88 supply. Applying power at the leads of C1025, I could also check the | 88 supply. Applying power at the leads of C1025, I could also check the |
| 89 behavior of the Q1020/Q1021 stage. Their purpose is to regulate the | 89 behavior of the Q1020/Q1021 stage. Their purpose is to regulate the |
| 90 supply voltage for the U1030 main oscillator. | 90 supply voltage for the U1030 main oscillator. |
| 91 | 91 |
| 92 .. image:: {filename}/images/tek2445/psu_prereg_test.jpg | 92 .. image:: {static}/images/tek2445/psu_prereg_test.jpg |
| 93 :alt: Testing the main control oscillator. | 93 :alt: Testing the main control oscillator. |
| 94 | 94 |
| 95 At power-up time, when the oscillator has not yet started, R1020 fill | 95 At power-up time, when the oscillator has not yet started, R1020 fill |
| 96 C1025 from the input high voltage DC. When the voltage on C1025 | 96 C1025 from the input high voltage DC. When the voltage on C1025 |
| 97 reaches about 21V, Q1021 is activated, powering U1030 (from C1025), | 97 reaches about 21V, Q1021 is activated, powering U1030 (from C1025), |
