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Thread: Horror! ABI ICT24 Chip tester Faulty - and Probable Fix

  1. #1
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    Default Horror! ABI ICT24 Chip tester Faulty - and Probable Fix

    Hi - just wanted to post a process of repair for anyone faced with a similar issue - you must own an ABI ACT-24 chip tester or its rebranded RS Components brother (like mine) for tis to be relevant to you.


    For the 3rd time, I found myself testing all 128 2114 RAM ICs in my IMS 8000 S100 computer


    2/3rds through the first board and THIS appears!

    ABI ICT24 Fault 2.jpg

    First thought - this thing must be fixable - take the lid off, out with the logic board and lets Dremel/wire brush the pins on the 2 BIOS EPROMS! Put it back together and nothing! Unsurprising.

    Next - calm down! Re visit the one site on the innerweb that actually has detailed info on this particular chip tester...

    http://www.jammarcade.net/abi-ict-24...ter-tech-info/

    Half way down the page, this genious has disassembled the BIOS on his unit and actually worked stuff out - as in what the fault codes mean!!! I quote:

    Fault 2:
    One of the IO¬’s on PORTB is tied to VCC.
    The software sets all of the IO pins on PORTB to logic LOW and reads the states back. If any pins are found to be logic HIGH on PORTB then this will result in FAULT 2.


    WHATS A PORTB!!!!???

    Ok, next step - further up the page he 'derives a memory map????!! Huh? As follows...

    Once I had drawn it out I derived the following memory map
    $0000-$3fff ¬– ROM1
    $4000-$7fff ¬– ROM2
    $8000-$87ff ¬– RAM
    8255 (IC1)
    $c000 ¬– PORTA
    $c001 ¬– PORTB
    $c002 ¬– PORTC
    $c003 ¬– Control
    8255 (IC2)
    $c004 ¬– PORTA
    $c005 ¬– PORTB
    $c006 ¬– PORTC
    $c007 ¬– Control
    8255 (IC3)
    $c008 ¬– PORTA
    $c009 ¬– PORTB
    $c00a ¬– PORTC
    $c00b ¬– Control
    8279 (IC
    $c00c ¬– Data
    $c00d ¬– Control


    ¬….IC1...IC2...IC3 - all 8255s!! I CAN DO THIS!!

    Those are the big PPI chips I can see in front of my face - lets look closer...

    ABI ICT24 Logic Board.jpg

    ...Ok, I can see lots of bus lines going from all those PPI chips to the row of 74LS125 chips below - 'MUST' be something to do with one of those??

    'If any pins are found to be logic HIGH on PORTB then this will result in FAULT 2'

    My dimwit diagnosis - one of those 74LS125 chips is holding one of those PPI chip pins logic High!

    Forget the Logic Probe - lets desolder all 6 of those chips and test them in my End Of The World logic chip tester - the MiniPro TL866A! and YES! It supports the 74LS125!! We can do this!

    Desldering¬…

    ABI ICT24 Removed 74LS125 ICs.jpgABI ICT24 Component Side ICs Removed.jpgABI ICT24 Solder Side Removed ICs.jpg

    TESTING! TESTING! TESTING! and yessssss!!

    ABI ICT24 Faulty 74LS125.jpg

    We have a probable suspect - lets socket the thing!!

    ABI ICT24 Run Out Of Sockets 02.jpg

    Damnaggit - run out of 14 pin sockets!! Lets Make one!

    ABI ICT24 Make Socket Dremel Before.jpgABI ICT24 Make Socket Dremel After.jpg

    Now we have 6 14 pin sockets where once we had 6 74LS125's

    ABI ICT24 Which is the Faulty IC.jpg

    But which is the faulty chip?? THIS one...

    ABI ICT24 Logic Board back in case.jpg

    Do I have any spare 74LS125?? NOOOOOOOOOOOOO!!!!!!!

    5 Now on Order...

    https://www.ebay.co.uk/itm/112367499720

    Along with 20 14 pin IC sockets:

    https://www.ebay.co.uk/itm/223096101340

    Stay Tuned For Next Weeks Installment! Will Bobby Die? Will Su-ellen Wake up in the shower and realise 6 weeks of filming was all a dream? WILL THE ABI ICT-24 GET FIXED!!!!!
    Attached Images Attached Images
    Last edited by alan8086; March 18th, 2019 at 01:09 PM.

  2. #2
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    I don't know why I attached a thumbnail at the end!? Don't know how that happened - Edit timed out.

    Oh, I had left the chip tester in continuous test loop mode with a 2114 chip - came back a good hour and a half later and that GD74LS125A chip had died! Wont leave it that long in future!
    Last edited by alan8086; March 18th, 2019 at 01:24 PM.

  3. #3
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    Pleased to say my ABI ICT-24 Logic IC Tester is working again. The 5 74LS125 ICs arrived today.

    I've continued to test all the ICs on my 4 16k static RAM boards and found 2 glue logic chips to be defective - more spare parts ordered!

    WP_20190320_15_32_36_Pro_LI.jpgWP_20190320_15_33_45_Pro_LI.jpgWP_20190320_15_34_20_Pro_LI.jpgWP_20190320_15_34_24_Pro_LI.jpg

  4. #4

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    A couple of things.
    I have never used a chip tester to debug equipment.
    I find it unlikely that one could have that many parts failing unless there was a power supply issue or poor static handling.
    Dwight

  5. #5
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    Same here. I've got an EPROM programmer that can identify many TTL chips, but not test them.

    The LS125s are simple enough to debug in situ--they're just quad tristate buffers--no fancy memory inside of them; very straightforward.

  6. #6

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    And same here, I've never used an IC tester, most of the electronic boards that I repair have non-socketed logic chips, so I must identify the problem(s) and remove only the problematic chips.
    However sometimes I think I'd like to have the famous HP logic comparator

    Frank IZ8DWF

  7. #7

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    HP had a current probe at one time as well. Say you have a net that is stuck at 0 or +5V. The part driving the short may get hot if to +5V but otherwise which of maybe 5 or 6 loads are the problem on a soldered board. The probe had 4 close contacts. One could read out the current flowing in an IC lead. Not with any accuracy but one could still clearly see the difference between 20ma and 600ua. I evaluated one for production test years ago at Intel but even though it worked quite well, it was rare to have a new part with a shorted input. A 'scope to see voltages was usually enough to find problems and shorted nets were usually board trace or solder bridges on new units.
    I'd love to have on of those probes today anyway.
    Dwight

  8. #8
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    Dwight, I'm still hoping that an HP Logic Dart will fall on my desktop one of these days...

  9. #9
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    Yes, I know - a chip tester is a quick and dirty troubleshooting method, possibly not very quick either if you have experience and knowledge regarding the use of logic probes etc

    My goal is to have a working S100 system - one that works for long enough so that I can learn the basics. Chip testers get me there quickly, but I learn little along the way.

    I will check the voltages from the linear power supply with multimeter and oscilloscope, need to check the regulators too.

    I also need to glue back together the head load pad that fell off the B: Drive earlier today. Maybe an excuse to buy a 3d printer? No one sells head load pads anymore!

  10. #10
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    Cool

    I have all three HP units - logic probe, pulser and current tracer. I also have this:

    http://www.jammarcade.net/abi-ict-24...ter-tech-info/

    Plus all the chips in my IMS 8000 computer are socketed. What would be your preferred tool?

    I does take about 2 hours to desocket one at a time every chip on all 4 static RAM boards, but the ABI chip tester will test every IC on there, identify unknown chips, do a continuous test loop on a device - if you look at the supported device list you will see how invaluable a tool it is. I also have an ABI DDS 40 XP - same type of tester but more advanced. You can program it in TestBASIC to test devices not currently supported.

    Without these chip testers, I'd be a dead loss - this is how I worked out which two 2114 RAM chips had failed after my IMS 8000 sat on a shelf for 4 years

    It now works, and my IMS8000 can now format floppy disks!

    Quote Originally Posted by iz8dwf View Post
    And same here, I've never used an IC tester, most of the electronic boards that I repair have non-socketed logic chips, so I must identify the problem(s) and remove only the problematic chips.
    However sometimes I think I'd like to have the famous HP logic comparator

    Frank IZ8DWF

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