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5150 and 5160 problems

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    5150 and 5160 problems

    Hi guys,

    I don't get on here much but was wondering if anyone could help me out a bit.

    I've got an IBM 5160 with 64-256k board that I've owned for about 15 years. It has been in storage for the last 7, and it won't power on. The power supply showed 0v on all lines, until I unplugged it from the motherboard, at which point it came good. So I'm assuming there is a tantalum capacitor shorted on the board (or maybe a bad expansion card - haven't pulled them yet). Can anyone tell me the most likely culprit? I've got a few spare caps but not enough to change out all of them at the moment.

    I've also got a 5150 64-256k board I bought for $1 online (lol) and it constantly blows the C6 tantalum when replaced. Without it, it boots fine. Should I just leave it out or has anyone had this as a sign of further problems?

    Thanks in advance for any help received!


    That you can read voltages says that you must have a multimeter. That's good. Leave the PSU unplugged, set your meter on the continuity test setting (or low ohms if you don't have one of those) and check at the power supply connector between ground and the various supply pins (+5, -5, +12 and -12). See if any measures short. That will narrow things down quite a bit.
    Reach me: vcfblackhole _at_ protonmail dot com.


      There is multiple connected in parallel across the power lines, so a bit of guess and check is required.
      Using a multimeter, find which power lines / capacitors show a low resistance (often 0 ohms). For the caps, focus first on the caps near the PSU connector and near the ISA slots.
      Because they are connected in parallel - you wont be able to easily find the specific culprit - but this guides you to finding the likely suspects.

      If your multimeter is able to read (even if inaccurately) down to 0.01 ohm resolution, you might even be able to tell which location is more likely.

      modem7 has been good enough to keep track of faults, - C56 and C58 are popular, and I've had to remove those myself.


      What you really should do: desolder all of them, install new ones
      What you should do: desolder offending caps one by one until resistance increases, then replace any that were removed
      What I do: grab likely suspect with fingers, bend back and forward until it comes off - repeat until the short goes away (then solder in replacements later if you want to or if the machine has trouble after)

      I'm not sure what's going on with your 5150 board, unless you installed the cap backwards or it's really old stock?
      Twitter / YouTube


        Thanks to both of you for the replies. I'll do as you said and check resistance on the motherboard's power connectors and take it from there.

        I'm pretty sure I put the (two legged) replacement cap in the 5150 correctly - positive lead to the center hole and negative to either of the two other holes (I chose the bottom one)... is that right?

        It could be old stock... I didn't think of that. I bought 6 of them from an old bloke at a local electronics shop. Seeing it's working for now I think I'll just leave it out. I intensely dislike the firecracker experience when they get upset.

        Thanks! I'll post an update after I play further with the 5160 tonight.


          Sorry, I posted a reply but it somehow disappeared.

          Thanks very much for the replies guys! I'll check the resistance on the 5160's power connectors tonight and take it from there.

          The 5150 seems to work fine now - I left it powered on for a good 15 minutes. I hadn't thought of the new cap being bad too, I bought it from an old guy at a local electronic shop. It might have been there a while.

          Cheers! I'll keep you posted with progress!


            Originally posted by bobba84 View Post
            I've also got a 5150 64-256k board I bought for $1 online (lol) and it constantly blows the C6 tantalum when replaced. Without it, it boots fine. Should I just leave it out or has anyone had this as a sign of further problems?
            I have just looked at a 64KB-256KB 5150 motherboard, and looked at the corresponding circuit diagram. I cannot find a C6 on either.


              Originally posted by SpidersWeb View Post
              modem7 has been good enough to keep track of faults,
              That mirror is almost 2 years old. Best to point to the master:


                Hi guys, thanks for all your help. Just an update...

                Sorry! I meant to say C7 on the 5150. It's next to the keyboard port.

                I followed the instructions modem7 sent me for the minimal diagnostic. The 5160 board itself has all the right resistance and voltage readings. It ended up being a shorted tantalum on my 384k expansion card causing the power supply to cut out. I removed it and it now powers on. But even with no cards installed it won't POST or beep at all when powered on.

                I got to the end of the instructions where it asked me to swap the RAM chips in banks 0 and 1 - which I did, but it still won't post.

                Everything seems fine, but it's dead. The speakers makes a 'tick' noise when power is applied, but I remember it doing this when first powering on even when it worked.
                I also pressed on all socketed IC's to make sure they were snugly fit.
                Is there anything else I can try? Or is my board likely dead?

                Again thanks so much - you guys are awesome!



                  Originally posted by modem7 View Post
                  That mirror is almost 2 years old. Best to point to the master:
                  Ah sorry, that's pretty bad of me (I'm a software dev, I should know better). Thanks for the fix.
                  Twitter / YouTube


                    So how much RAM is on the Motherboard right now? 256k? Did you remember to set the jumpers to indicate that amount? I am guessing you have the 384K RAM card still pulled out? Just my guess as to what is happening. Good luck


                      Only bank 0 is required for boot.
                      If the amount is incorrect on the switches it'll still start up and beep.
                      Twitter / YouTube


                        It has 256k on board, with jumpers set correctly. All cards removed. I might pull the board out of the case tonight and check the bottom for dry joints, etc. It's all I can think of at present. The power supply runs the 5150 board fine, so I'm pretty sure that's okay.


                          Originally posted by bobba84 View Post
                          I got to the end of the instructions where it asked me to swap the RAM chips in banks 0 and 1 - which I did, but it still won't post.
                          The failure of any of many components on the motherboard will cause an 'appears dead' symptom. Faulty RAM in bank 0 is one relatively common cause, and that is why there was the suggestion to try swapping bank 1 RAM with bank 0 RAM. And it's easy to do on a 5160 motherboard.

                          But you cannot cross out faulty bank 0 RAM off the list yet. It could be that you have multiple faulty RAM chips scattered over both banks 0 and 1. If so, swapping those banks does nothing (other than perhaps rectifying a bad electrical connection). Your 5160 motherboard is the 256K type, and that means that all four banks use the same type of RAM chip (although possibly of different manufacturer). The chances of faulty RAM in all four banks has to be pretty low. Try swapping bank 2 into bank 0, and if that does not change things, then try swapping bank 3 into bank 0. Of course, while you are doing that, use ESD protection practices.

                          Your 5150 motherboard is operational. You could try swapping the 8088 CPU chip from that into the 5160.

                          Failure of a BIOS ROM is another possibility. Do you have an EPROM programmer and 27256 (or 27C256) EPROMs? If so, you could try the Supersoft/Landmark diagnostics at [here], or make replacement BIOS ROM chips from the images at [here]. If not, I can post EPROMs to you.

                          Originally posted by bobba84 View Post
                          The speakers makes a 'tick' noise when power is applied, but I remember it doing this when first powering on even when it worked.
                          Yes, ignore that. It results from a surge of current going through the speaker when power is applied to the motherboard.


                            Thanks modem7. I'll try swapping the RAM from the other banks first, then look at the BIOS. I have an eprom programmer, but no chips of that size. I'll buy one from the local guy if my bios appears bad.

                            Appreciate all your help!


                              Hi again modem7,

                              I have had it with my EPROM programmer. It's a cheap nasty one and I've wasted two 27c256's on it!

                              I noticed you are also in Melbourne - would it be okay if I took you up on the offer of replacement BIOS chips? I'll send you money to cover them!