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Thread: IBM 5154 Problems & Electrolytic Caps Question

  1. #1
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    Default IBM 5154 Problems & Electrolytic Caps Question

    A long while ago I got an IBM 5154 in very good condition (it was not cheap though) to go with my IBM 5162. I was very pleased with the setup but one thing kept bothering me. The monitor had this green tint to it when you first turned it on, but it went away as you kept the machine running. I assumed this was the fault of old electrolytic capacitors, and since I wanted to try out my new desoldering gun, I decided to replace all of them. However, when I replaced all of them, it still had some problems. The green tint was gone. However, the display was a bit shaky and looked like it was vibrating ever so slightly. Sometimes it would pulse in and out, as if the display got slightly bigger and slightly smaller. Every so often I would hear popping noises, but no smoke or hissing so I wasn't sure if it was a capacitor bursting or not. Eventually there was a popping noise accompanied by the entire display turning solid green. At that point, I just set the monitor aside for later. Eventually, when I came back to it, it wouldn't even turn on. The power indicator light would come on, but there was no white raster and no video signal. It still makes the high pitched noises when syncing to the signal, but displays no picture. I'm now feeling like I replaced one of the capacitors with one of the wrong value. I made sure to replace all of the with identical replacements, except for two which were rated for 40v. I couldn't find ones for 40v so I replaced them with 50v ones. I checked all of the big turquoise resistors and none of them were shorted. I was wondering if anyone had a list (or could make one) of all of the values of the electrolytic caps of the 5154 so I could double check that I replaced all of the old ones correctly. If anyone has any insight as to what is happening, please feel free to share with me.

  2. #2
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    Perhaps some caps were replaced "backwards"? (Don't always trust board markings!)

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    On which boards did you replace capacitors ? The power supply board is where the capacitors usually fail.
    Its in a metal cage, runs hot, and the original capacitors temp rating was only at 85C. I have two 5154's
    and have replaced all electrolytic capacitors in the power supplies. Have never needed to replace them in
    any of the other boards.

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    I replaced the capacitors in the power supply, video board, and main board. I even replaced the capacitor on the neck board. When caps fail, they excrete electrolyte over the board, right? So if the capacitor failed, I should be able to see fluid below it, right? To your knowledge, are there any misleading board markings where I could have put in the capacitor backwards? I checked all of them to make sure they matched the board's markings.

  5. #5
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    Caps can fail without spilling their guts. Sometimes, it's just a dead short.

    There have been instances where board markings are wrong, but I don't know about the 5154.

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    These pages below show the expected voltages on the power supply connectors.
    I would start by checking these.

    Have you removed or replaced those two oil filled capacitors across the AC line ?
    .1 uf X2 C5/C6? I've had these caps blow on both monitors and they make a mess
    and a lot of smoke. They wouldn't cause a problem like what you're seeing but
    its definitely a good idea to get those out before they blow. The monitor will work
    fine without those, so you can safely remove them and replace later with the
    correct parts, need to be X2 rated.



    Page11.jpg
    PowerSupplySchematic1.jpg
    PowerSupplySchematic2.jpg
    Last edited by mikey99; July 13th, 2019 at 02:27 PM.

  7. #7

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    Quote Originally Posted by willmurray461 View Post
    A long while ago I got an IBM 5154 in very good condition (it was not cheap though) to go with my IBM 5162. I was very pleased with the setup but one thing kept bothering me. The monitor had this green tint to it when you first turned it on, but it went away as you kept the machine running. I assumed this was the fault of old electrolytic capacitors, and since I wanted to try out my new desoldering gun, I decided to replace all of them. However, when I replaced all of them, it still had some problems. The green tint was gone. However, the display was a bit shaky and looked like it was vibrating ever so slightly. Sometimes it would pulse in and out, as if the display got slightly bigger and slightly smaller. Every so often I would hear popping noises, but no smoke or hissing so I wasn't sure if it was a capacitor bursting or not. Eventually there was a popping noise accompanied by the entire display turning solid green. At that point, I just set the monitor aside for later. Eventually, when I came back to it, it wouldn't even turn on. The power indicator light would come on, but there was no white raster and no video signal. It still makes the high pitched noises when syncing to the signal, but displays no picture. I'm now feeling like I replaced one of the capacitors with one of the wrong value. I made sure to replace all of the with identical replacements, except for two which were rated for 40v. I couldn't find ones for 40v so I replaced them with 50v ones. I checked all of the big turquoise resistors and none of them were shorted. I was wondering if anyone had a list (or could make one) of all of the values of the electrolytic caps of the 5154 so I could double check that I replaced all of the old ones correctly. If anyone has any insight as to what is happening, please feel free to share with me.
    The story does sound like you cured the original fault with the re-capping and introduced a new fault. The type of fault sounds like one of the replaced capacitors was installed in reverse and failed later. It could have been a coincidence and the new fault is unrelated to the first one or the recapping. A capacitor of the wrong value would unlikely do it, most likely one got installed in reverse. So double check each one first and check on a meter for shorts and use an ESR meter to check each one in circuit.

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    Here's a thought: does the 5154 use a nonpolar cap in its PSU (like most SMPSUs do)? Did you replace it with a similar nonpolar unit?

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    I did replace the x2 caps, so that shouldn't be the problem. I kept all of the original caps, and none of them seem to be non polar. I'll go check to see if any of them were installed backwards again. If they were, would they be shorted, or would they read OL (open circuit)? I don't have an ESR meter, but I do have a multimeter.

  10. #10

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    Do you have an oscilloscope? It's a must-have when messing with monitors. Be careful with that thing, CRTs can be lethal if you accidentally touch the wrong thing. Stay away from the anode cap, the neck board, and the flyback when servicing a CRT device.
    There was most likely nothing wrong with your monitor as far as the green tint goes. Sometimes when CRTs get old, the guns can take longer to warm up and start emitting. Sounds like in your case the green one was more active than the red and blue. Once the CRT warms up to normal operating temperature, it will balance out. If I remember correctly, IBM listed the warm-up time for the 5154 as either 20 or 30 minutes. That's how long it takes for the filament to warm up everything in the gun assembly to temperature and for all the electronics to balance out temperature wise. A full recap was most likely not necessarily.

    I would start on the video board. Thoroughly inspect it with a magnifier under bright light to find any obvious physical damage, if any exists. If you have access to an oscilloscope, start at the video input and trace the video signal through the circuit. I would advise you use a clip-type lead, and only move the lead when the monitor is off to avoid shorting anything/getting shocked. While it could be the video board, the presence of a loud "pop" makes me lean more towards the HV board.

    There are a few caps in the monitor which are specified to be low-ESR type caps. Did you replace those with low-ESR replacements? If not, the resistance of the cap could cause it to heat up during operation, causing voltage fluctuations and eventually component failure. This might explain the display jitter.

    Good luck in your repair, and be safe!

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