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Thread: Repair of 5160 XT power supply

  1. #11

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    Hi,

    I am restoring an IBM 5160. The power supply was a bit rusty.

    The problem:

    I think the +12 volts is short circuited with the ground. When I measure it with multi-meter for connection (12 volts and one ground) it beeps continuously. And values are similar to when connecting two grounds.

    That is not normal, right? I should not expect when I power it up that this problem will disappear?

  2. #12
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    Quote Originally Posted by tonata View Post
    I think the +12 volts is short circuited with the ground. When I measure it with multi-meter for connection (12 volts and one ground) it beeps continuously.
    The fact that your multimeter is beeping, suggests to me that you have your multimeter in the 'continuity' setting. For future reference, note that the continuity setting can sometimes be misleading. See the comment at [here].

    In the case of the IBM 5160, the resistance on the +12V line should not be low enough to trigger your multimeter's continuity beep, and so it sounds like there is a problem there.

    The problem cause could be on the motherboard, or on an expansion card.

    Try the procedure at [here]. If the cause is on the motherboard, then I am expecting that the procedure will have you remove/replace motherboard capacitor C56.

  3. #13

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    Thank you for your response. Yes, 'continuity'.

    I am afraid the power supply will damage the motherboard if it not functioning correctly. What are the chances of this happening? I still have not connected the two.

    Question 1: Probably a capacitor is responsible for the +12 volts lack of resistance? How should I debug it?

    I have also acquired a HEDEN PSX A968 350 Watt power supply with 20 pins and one 6 pin P8/P9 type of connector. It has the 5,12,-12 and -5 volts. I still need to re-wire it to the IBM 5160 specification. I have the P8 and P9 connectors also.

    The HEDEN is +5V@25.0A, +12V@15.0A, -5V@0.6A, -12V@0.6A which seems compatible with IBM 5160 power ratings.

    And PWR_OK (grey) on the HEDEN = Power Good on the IBM 5160. The green PS_OK (HEDEN) would not be used.

    Questions 2: Would this HEDEN PSX A968 power supply be really compatible?

  4. #14
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    Quote Originally Posted by tonata View Post
    I am afraid the power supply will damage the motherboard if it not functioning correctly. What are the chances of this happening? I still have not connected the two.
    Damage could result through over-voltage. For example, the power supply generating +6V on the +5V line.

    I expect that a decent power supply will contain circuitry to detect an over-voltage situation, and if detected, shut the power supply down.
    Some 'cheap' power supplies may not have circuitry to detect an over-voltage situation.

    Quote Originally Posted by tonata View Post
    Question 1: Probably a capacitor is responsible for the +12 volts lack of resistance? How should I debug it?
    Use the procedure at [here].

    Quote Originally Posted by tonata View Post
    I have also acquired a HEDEN PSX A968 350 Watt power supply with 20 pins and one 6 pin P8/P9 type of connector. It has the 5,12,-12 and -5 volts. I still need to re-wire it to the IBM 5160 specification. I have the P8 and P9 connectors also.
    The HEDEN is +5V@25.0A, +12V@15.0A, -5V@0.6A, -12V@0.6A which seems compatible with IBM 5160 power ratings.
    And PWR_OK (grey) on the HEDEN = Power Good on the IBM 5160. The green PS_OK (HEDEN) would not be used.
    Questions 2: Would this HEDEN PSX A968 power supply be really compatible?
    You have established that the HEDEN generates all of the required voltages, and can do so at greater power than the IBM XT power supply. You have also established that the HEDEN generates a signal that is the same as the POWER GOOD signal generated by the IBM XT power supply. So, it sounds like the HEDEN will work.

    (By the way. If the HEDEN did not generate an equivalent to the POWER GOOD signal, there are ways around that. An example at [here].)

  5. #15

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    Quote Originally Posted by tonata View Post
    ....I still have not connected the two........
    I'm a bit confused here, When you took those readings, did you take them from the Motherboard +12v - GND connector with nothing connected to the Motherboard ?, Or did you have the PSU on the bench and took those readings from the power connector of the PSU with nothing connected to the PSU ?.

    What make of PSU is it, 240v 130W Schrack or ??, Have you powered this PSU up on the bench and checked the DC output voltages with nothing connected to the PSU or with a load connected ?.

  6. #16

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    Quote Originally Posted by Malc View Post
    I'm a bit confused here, When you took those readings, did you take them from the Motherboard +12v - GND connector with nothing connected to the Motherboard ?, Or did you have the PSU on the bench and took those readings from the power connector of the PSU with nothing connected to the PSU ?.

    What make of PSU is it, 240v 130W Schrack or ??, Have you powered this PSU up on the bench and checked the DC output voltages with nothing connected to the PSU or with a load connected ?.
    I took them with nothing connected. No power from the electrical grid and not connected to the motherboard. A simple multi-meter was used.

  7. #17

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    Quote Originally Posted by modem7 View Post
    Damage could result through over-voltage. For example, the power supply generating +6V on the +5V line.

    I expect that a decent power supply will contain circuitry to detect an over-voltage situation, and if detected, shut the power supply down.
    Some 'cheap' power supplies may not have circuitry to detect an over-voltage situation.


    Use the procedure at [here].


    You have established that the HEDEN generates all of the required voltages, and can do so at greater power than the IBM XT power supply. You have also established that the HEDEN generates a signal that is the same as the POWER GOOD signal generated by the IBM XT power supply. So, it sounds like the HEDEN will work.

    (By the way. If the HEDEN did not generate an equivalent to the POWER GOOD signal, there are ways around that. An example at [here].)
    The HEDEN gives 5V after connecting the PS_ON and the ground. So it should be OK. The timings explained on wikipedia are not important I suppose as far as there is 5V at the end.

  8. #18
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    Quote Originally Posted by tonata View Post
    The HEDEN gives 5V after connecting the PS_ON and the ground. So it should be OK. The timings explained on wikipedia are not important I suppose as far as there is 5V at the end.
    In theory, there is a timing consideration.

    In many motherboard designs, after power-on, the motherboard is held in the reset state for a short period. One of reasons may be the 8088. Its description of the reset pin includes, "The signal must be active HIGH for at least four clock cycles." Other motherboard chips may have their own requirements.

    If you look at the Intel diagram at [here], the capacitor and resistor at far left result in the 8088 CPU's reset pin being held high for a short period after power-on. That capacitor and resistor is what IBM used in the PCjr, but in the IBM 5160, IBM chose instead to have RESET controlled by a POWER GOOD signal from the power supply. Therefore, the POWER GOOD signal should not become active until a short period after the 5160 motherboard receives +5V.

  9. #19
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    Quote Originally Posted by Malc View Post
    I'm a bit confused here, When you took those readings, did you take them from the Motherboard +12v - GND connector with nothing connected to the Motherboard ?, Or did you have the PSU on the bench and took those readings from the power connector of the PSU with nothing connected to the PSU ?.

    What make of PSU is it, 240v 130W Schrack or ??, Have you powered this PSU up on the bench and checked the DC output voltages with nothing connected to the PSU or with a load connected ?.
    Quote Originally Posted by tonata View Post
    I took them with nothing connected. No power from the electrical grid and not connected to the motherboard. A simple multi-meter was used.
    I have made an assumption (shame on me) that you are dealing with two problems, a power supply problem and a motherboard problem.

    If we go back to your original question, with the subject being a 'continuity' measurement in the power supply between the 12V line and the ground line, then yes, I would not be surprised if the multimeter indicated continuity.

    Why do you believe that your power supply is faulty?

    As Malc suggested, in case you are unaware, most switch mode power supplies for the IBM 5160 cannot power up unloaded; they need to be adequately loaded. When loading the power supply, you need to use something that is known to be an adequate load, and known to be good. For example, you may decide to use the 5160 motherboard as the load, but what if there is a short circuit in the motherboard. That would overload the power supply, stopping it from working.

  10. #20

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    Quote Originally Posted by modem7 View Post
    ....If we go back to your original question, with the subject being a 'continuity' measurement in the power supply between the 12V line and the ground line, then yes, I would not be surprised if the multimeter indicated continuity....
    Yep, I grabbed a working 240V 130W Schrack PSU and measured the resistance of the +12V - GND line and got a stable 21.6 Ohm's, If i had my meter in continuity mode it would beep as my meter beeps at anything less than 100 Ohm's. Obviously it depends on the PSU manufacture / design.

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