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Diagnosing KIM-1 short

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    #16
    ok good job.
    My guess the last owner plugged the wrong voltage, something much higher than 5v [maybe he had the 5v and 12v swapped], into that KIM-1 and the zener sacrificed itself.
    All in the name of rock 'n roll
    Because they must have left it on with the higher voltage just a little too long for that zener to dissipate all that extra power.

    The oscillator cap has such a low ESR that it can be disregarded. Your ESR meter probably couldn't register any reading on such a low capacitance. That meter must have a specific range, in general for electrolytic caps.
    Dan Roganti
    my corner of cyberspace http://www.rogtronics.net/blog
    Vintage Computer Federation http://www.vcfed.org/

    Comment


      #17
      Radioshack has no 6.3v so I ordered a few. What would happen if I used a 3.8v (too low) or 11v (too high) instead (just curious)?

      In the meantime when I first ran a power on test I had a clip lead on the circuit to measure the 5V and it melted it within a split second. The Zener might have sacrificed itself, but more damage down the line is expected.
      @ BillDeg:
      Web: vintagecomputer.net
      Twitter: @billdeg
      Youtube: @billdeg
      Unauthorized Bio

      Comment


        #18
        Originally posted by billdeg View Post
        Radioshack has no 6.3v so I ordered a few. What would happen if I used a 3.8v (too low) or 11v (too high) instead (just curious)?
        ok, don't use anything lower than a 5v zener. It will start to conduct and overheat because there isn't any current limiting resistor in series with that.
        Just leave that spot empty until you get the new parts in. No sense in putting the 11v volt, it won't protect the 5v parts since it's a higher voltage rating.
        You can still power up the board without this part. Just watch that the power connections don't get swapped around by mistake.

        Originally posted by billdeg View Post
        In the meantime when I first ran a power on test I had a clip lead on the circuit to measure the 5V and it melted it within a split second. The Zener might have sacrificed itself, but more damage down the line is expected.
        oh wait, did you check the in-circuit resistance on the 5v power and 12v power yet ? [remove power supply]
        See my earlier post for the in-circuit resistance values.
        Dan Roganti
        my corner of cyberspace http://www.rogtronics.net/blog
        Vintage Computer Federation http://www.vcfed.org/

        Comment


          #19
          +5v .478 k ohm
          +12v 2.9 m ohm

          The power supply itself is very solid. It is a newer one, seems to maintain exactly 5.0 with a number of resistors are in line. I do have questions about how to measure the caps in circuit if possible by comparing a known-working unit rather than removing one leg to test out of circuit, but if need be I will remove each. Same goes with the resistors, but I suspect a cap is more likely to have gone bad.

          There is no 6.2v Zener diode in circuit (removed the bad one). I have seen +5.0v readings (exactly) throughout the board indicating a steady regulation. After removing the zener there is no complaint from the power supply.

          Next I plan to work through the board/schematic, but if you have any test points to confirm let me know. I have an oscilloscope, logic probe, etc ready to go.

          b
          @ BillDeg:
          Web: vintagecomputer.net
          Twitter: @billdeg
          Youtube: @billdeg
          Unauthorized Bio

          Comment


            #20
            Originally posted by billdeg View Post
            +5v .478 k ohm
            +12v 2.9 m ohm
            ok ,looks good
            It doesn't appear then to be any major shorts on the mainboard.
            On the +5v you like to type 0.478Kohm, since it's viewed like that on the DMM, and it's easier to read on here

            Originally posted by billdeg View Post
            The power supply itself is very solid. It is a newer one, seems to maintain exactly 5.0 with a number of resistors are in line.
            That's good news. Considering what stress it might have gone thru if it had been wired incorrectly to the mainboard and damaged that zener

            Originally posted by billdeg View Post
            I do have questions about how to measure the caps in circuit if possible by comparing a known-working unit rather than removing one leg to test out of circuit, but if need be I will remove each. Same goes with the resistors, but I suspect a cap is more likely to have gone bad.
            I guess you mean measuring the ESR and if you have a "In-Circuit" ESR meter. Not all of them are the same type. Some are only "out-of-circuit". Your ESR70+ meter can check Caps "in-Circuit", so you can go ahead and take the ESR measurements of the Electrolytics.

            Originally posted by billdeg View Post
            There is no 6.2v Zener diode in circuit (removed the bad one). I have seen +5.0v readings (exactly) throughout the board indicating a steady regulation. After removing the zener there is no complaint from the power supply.
            Sounds like it's looking good so far.


            Originally posted by billdeg View Post
            Next I plan to work through the board/schematic, but if you have any test points to confirm let me know. I have an oscilloscope, logic probe, etc ready to go.

            b
            The basic thing to verify is the CPU oscillator is working fine, on pin.39. Just use the scope for the that, with the Horiz set to about 5us/div and the Vert set to about 2v/div to view enough cycles on the screen.

            One thing I noticed is it hard to find the original schematics for the KIM-1. All I ever see online are copies which are not exactly the same as the original KIM-1. So finding the signals on chips and their pin numbers are a chore still.

            You should try to run some of the examples in the user manual
            If you don't have the manual, there a copy online here
            http://users.telenet.be/kim1-6502/6502/usrman.html
            Dan Roganti
            my corner of cyberspace http://www.rogtronics.net/blog
            Vintage Computer Federation http://www.vcfed.org/

            Comment


              #21
              Originally posted by Ragooman View Post
              <snip>

              The basic thing to verify is the CPU oscillator is working fine, on pin.39. Just use the scope for the that, with the Horiz set to about 5us/div and the Vert set to about 2v/div to view enough cycles on the screen.

              One thing I noticed is it hard to find the original schematics for the KIM-1. All I ever see online are copies which are not exactly the same as the original KIM-1. So finding the signals on chips and their pin numbers are a chore still.

              You should try to run some of the examples in the user manual
              If you don't have the manual, there a copy online here
              http://users.telenet.be/kim1-6502/6502/usrman.html
              Will try that next....real life work calls however, must wait. I have a full page poster schematic. I did not realize these are hard to find, maybe I will scan each block and post on my site so you can download, print, and assemble your own poster.

              I will put a logic probe on pin 39 and see what kind of pulse I am getting, plus compare with oscilloscope readout, will report back when I can.
              b
              @ BillDeg:
              Web: vintagecomputer.net
              Twitter: @billdeg
              Youtube: @billdeg
              Unauthorized Bio

              Comment


                #22
                This fellow has a very nice scan of the poster. I've spent many hours looking at it.

                http://www.pestingers.net/images/Ant...KIM_POSTER.jpg

                (It was nice to see one of my pictures referenced earlier in this thread.)

                Gilbert

                Comment


                  #23
                  Working through system..Power on 5V OK but no lights.

                  1. Removed shorted zener diode between application and expansion edge connectors. This solved problem with power supply (before pwr supp immediately hissed when power applied). Because my power supply is new and regulated I am told I don't need the zener, temporarily.
                  2. Replaced tant cap near 6502, was probably ok but it's a tant so it's a good idea to replace them when they're old just in case
                  3. replaced resistor near zener diode
                  4. getting pulse at pin 39 of CPU

                  At this point, applying power using a new 5V regulated supply returns exactly 5.00 volts in numerous places consistently, so now it's time to work through schematic.

                  1. pin 40 of 6502 goes low when RS (reset pressed)
                  2. It looks like a consistent wave on pin 39 and 3 on the 6502, but I'd like to see what a "good" one looks like. Mine is a slightly dirty looking wave but I don't expect a perfect sin wave either. I'd call it "probably good"
                  3. U16 pins 13, 12, 11 and 10 have a clock. 6502 A0/A1 have pulse
                  4. U4 (74145) D = nothing, A,B,C pulse after reset
                  5. U4 K0 = high, K5=high, K6=high, K7=high
                  6. transistor Q1 legs snapped off (both collector and emitter) need to replace (pnp transistor b>20 , vce>12 - 2n5371). tested base of Q2-Q6 by connecting base to ground with a 1Kohm resistor in the middle - all lit up.
                  7. tested 7406 in u17 using TTL tester - reports "passed".

                  I found some of these testing tips elsewhere on this site. thanks all.

                  Next - test the caps I guess.
                  @ BillDeg:
                  Web: vintagecomputer.net
                  Twitter: @billdeg
                  Youtube: @billdeg
                  Unauthorized Bio

                  Comment


                    #24
                    You need to ground the DECEN- line which is pin K on the application connector. That will cause U4 D input to be low, and then you'll see activity on K7, K5 and K0.

                    Comment


                      #25
                      wow. I did as you said and the KIM sprang to life ... at least now there is something on the display. I did not have pin K on the application connector grounded, I did not think I had to unless I was using the +12v...I was just grounding AA only all this time.

                      thanks...now to find a transistor for Q1 so I can read the most significant number of the addresses and test the ROM/RAM. When that's done I will attach to a teletype for input and storage.

                      UPDATE: RAM peeks shows ROM in memory matching 6530 listing, yay!

                      Bill
                      Last edited by billdeg; August 26, 2014, 09:23 AM.
                      @ BillDeg:
                      Web: vintagecomputer.net
                      Twitter: @billdeg
                      Youtube: @billdeg
                      Unauthorized Bio

                      Comment


                        #26
                        Originally posted by gcoville View Post
                        This fellow has a very nice scan of the poster. I've spent many hours looking at it.

                        http://www.pestingers.net/images/Ant...KIM_POSTER.jpg

                        (It was nice to see one of my pictures referenced earlier in this thread.)

                        Gilbert
                        I'm having a bugger of a time trying to view that webpage
                        I don't have any problems with other websites
                        Could it be that 512Kword BGP Routing Table Limit being hit again ?
                        Has anyone else tried that link ?
                        I checked with the usual "is-my-site-down" services and it says that website is definitely down
                        Could someone who has that copy upload it somewhere for us ?
                        Dan Roganti
                        my corner of cyberspace http://www.rogtronics.net/blog
                        Vintage Computer Federation http://www.vcfed.org/

                        Comment


                          #27
                          Originally posted by gcoville View Post
                          You need to ground the DECEN- line which is pin K on the application connector. That will cause U4 D input to be low, and then you'll see activity on K7, K5 and K0.

                          oh man, I looked closer at mine again and see that now too.
                          It was already wired that way but didn't recognize it.
                          I had to look it up online in the KIM-1 User manual - the one book I don't have.
                          The wiring is in the Power supply section[see link]
                          This is a Address Decode signal for any expansion hardware
                          http://users.telenet.be/kim1-6502/6502/usrman.html#F22
                          Dan Roganti
                          my corner of cyberspace http://www.rogtronics.net/blog
                          Vintage Computer Federation http://www.vcfed.org/

                          Comment


                            #28
                            Originally posted by billdeg View Post
                            wow. I did as you said and the KIM sprang to life ... at least now there is something on the display. I did not have pin K on the application connector grounded, I did not think I had to unless I was using the +12v...I was just grounding AA only all this time.

                            thanks...now to find a transistor for Q1 so I can read the most significant number of the addresses and test the ROM/RAM. When that's done I will attach to a teletype for input and storage.

                            UPDATE: RAM peeks shows ROM in memory matching 6530 listing, yay!

                            Bill
                            Glad to hear you got both of them working now
                            We might have to get ours all together and make a KIM-1 farm running some code for a display
                            Dan Roganti
                            my corner of cyberspace http://www.rogtronics.net/blog
                            Vintage Computer Federation http://www.vcfed.org/

                            Comment


                              #29
                              Originally posted by Ragooman View Post
                              Originally posted by ldkraemer
                              In your case, take a look at the LeakSeeker 89: http://eds-inc.com/product/leakseeker-89/

                              I know it expensive, but it shows you how it works. I wish I had one to play with, it did get me to thinking about cheaper solutions.
                              Hey, that one looks very interesting !
                              And it's way cheaper than the I-Prober 520
                              It does says it's only for dead-shorts, and not when it's a few ohms.
                              But it wouldn't hurt to add this on the bench.

                              I found a homebrew fluxgate current probe, similar to the I-Prober 520.
                              I'll have to look up the bookmark again. I think it was in the internet archive.
                              Found it, here's the link I think this is a great little project
                              Might want to back up this webpage in case it disappears.
                              http://avrs-at-leipzig.de/dokuwiki/e...ekte/fluxprobe
                              Dan Roganti
                              my corner of cyberspace http://www.rogtronics.net/blog
                              Vintage Computer Federation http://www.vcfed.org/

                              Comment


                                #30
                                I've used a better method of tracing shorts that even works on ground plains.
                                It always confuses people when I try to describe it but it can quickly find a shorted
                                part without anything other than some leads, a 4 digit ( prefered 5 digit) DVM and
                                a power supply with current limit.
                                One places the power supply from one side to the other of, say the ground
                                trace and limit the supply to about 2 or 3 amperes. ( yes, on the same trace,
                                not through the short ).
                                Place one meter lead on the trace that has the short.
                                With the other measure along the trace with the current flowing through it.
                                When you reach the short, the meter reads 0 volts.
                                If the supply has fingers, it may be necessary to move one of the supply
                                leads and probe along the finger.
                                On ground plains I up the current. You need to first probe one way across
                                the board and find the 0 volt line.
                                Move the supply leads to the other corner and probe to find another line.
                                X marks the spot of the short.
                                There are some other tricks like this that I use to find multiple shorts but
                                these are easier to show than describe in text.
                                Not more easter egging. You'll always know the exact cause of the short.
                                The voltage across the trace is so small that I've even used it to locate
                                a bad RAM that when soldered down was self selecting when powered up.
                                You just have to make sure the supply is isolated.
                                Dwight

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