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Diagnosing KIM-1 short

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  • billdeg
    replied
    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

    Leave a comment:


  • Ragooman
    replied
    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

    Leave a comment:


  • billdeg
    replied
    +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

    Leave a comment:


  • Ragooman
    replied
    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.

    Leave a comment:


  • billdeg
    replied
    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.

    Leave a comment:


  • Ragooman
    replied
    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.

    Leave a comment:


  • billdeg
    replied
    zener is bad reading .3 ohms (not m ohms).

    I don't believe the 10pF cap in earlier post was actually bad, too low to be measured by my ESR meter.

    Leave a comment:


  • billdeg
    replied
    OK...back from a round of disk golf and radioshack....I will test in order, I have all of the parts.

    Leave a comment:


  • Ragooman
    replied
    I may have missed you and you're probably on your to RS already.
    That little Cap up at the top above the 6502 is the Oscillator Cap
    That wouldn't short out the entire board and cause the power supply to hiss.
    You really don't want to skip steps here.
    Cause it'll make you go in circles and spend more time than necessary

    Leave a comment:


  • billdeg
    replied
    The 10pF tant cap at the top of the board was blown, the ESR tester registered nothing/cracked inside. Not sure if this is the only problem, but I am off to RadioShack to get a new one, and I guess a 6.2v zener if I don't already have one.
    thanks all.

    Leave a comment:


  • Ragooman
    replied
    Here's a diagram showing the +5v Caps - there's very little.
    There's also a Zener wired across +5v in there as a protection for when the incorrect power supply voltage is connected.
    This can be suspect too - just lift one leg and measure the resistance.
    KIM-1_+5v_Caps.jpg

    Leave a comment:


  • Ragooman
    replied
    Bill,

    Not sure where you placed the meter probes for the measurement
    But you want to measure with a Digital Multi Meter [DMM] first, not with the ESR meter, on the +5V power rail.
    You like to check the in-circuit resistance of the entire board first.

    but I attached a pic showing a very easy place to measure the resistance for +5v power
    KIM-1_+5V-crop.jpg

    and this shows an easy place to check the resistance for +12v
    KIM-1_+12v.jpg

    There aren't that many Cap's connected across the +5v power
    I can whip up another diagram for that too

    Leave a comment:


  • daver2
    replied
    Bill,

    I think you have connected +5 and GND to the correct pins. There is an image at http://gc.org/rc2011sc/et-3300_and_kim-1.jpg which seems to identify the power supply connections to the application connector. GND appears to be on the 'component' side of the PCB. If you hold the PCB with the keypad to the lower right; then the application connector is to the lower left. GND should be the 'top most' pin of the connector. +5V should be on the solder side of the GND connector (just below it depth wise). I think this confirms what you have done.

    C1 is also directly across the 5V supply - so you should be able to follow the + end of C1 to find the +5V connector pad and the other end to find the ground connector pad as a triple check.

    I would also be inclined to replace CR7 (6.2V Zener diode) as that is also directly across the power supply.

    The other thing to check would be the pads of the application connector (PCB side) themselves. As +5 is on one side and GND on the other; it is just possible (but unlikely) that a bridge could have occurred across them.

    After that - I would be inclined to put the KIM on a variable voltage DC supply and increase the voltage (whilst monitoring the current) to a point where the current is 'normal' for a KIM (i.e. you are not stressing the PCB power tracks) and then go around the chips with a thermometer or your finger looking for the hot one! There doesn't seem to be many decoupling capacitors on the KIM so I would be inclined to replace the odd one or two that are there on the off chance.

    Sorry, this is the worst type of fault to diagnose...

    Dave

    Leave a comment:


  • billdeg
    replied
    There is no resistance at all! I have a Peak ESR70+ cap tester. That will help a lot. I have printed out your suggestions and I will report back. I have spare caps, hopefully that's the cause and not something else.

    I should add I am using a new regulated power supply that I use for many other things. I will test the resistance of that too.
    b

    Leave a comment:


  • Ragooman
    replied
    Originally posted by ldkraemer View Post
    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.

    There are also some very helpful articles on EDN and EETimes about this subject
    http://edn.com/design/test-and-measu...acer-technique
    http://www.eetimes.com/author.asp?se...doc_id=1284424


    Originally posted by ldkraemer View Post

    http://electronics.stackexchange.com...ocation-on-pcb
    http://www.edaboard.com/thread31322.html
    http://www.hobbyprojects.com/test_ge...on_tester.html
    http://www.electroniq.net/other-proj...41-op-amp.html (If you want to make this one,
    I've found a better schematic of the 741 and associated circuit on the internet. PM me and I'll email you the better image.)
    Now these homebrew testers look very interesting too, I'm gonna add this to my list - thanks for sharing !


    Originally posted by ldkraemer View Post
    One other choice is to convert your Multimeter to a MilliOHM Meter and chase the Shorted condition, as the LeakSeeker would.
    http://users.tpg.com.au/pschamb/lom.html
    I like this homebrew version too
    I came across another one, but I have to check my bookmarks again and I'll post it
    This was a standalone version, using a panel meter, so you don't have to tie up your DMM

    Leave a comment:

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