System 11B - Diagnostic flashing

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  • System 11B - Diagnostic flashing

    Hi, new member. :)

    Trying to help a friend fixing a 11B from a Whirlwind, but the board is a basket case, had some alkaline damage, so somebody rebuilt the reset section and did a very bad job, it does however work.

    Main problem with the board is on power up, diagnostic flashes 60 times, then blanking 10, and repeat, no difference if U25 or U26 is removed, however sometimes you can make the board boot by touching an ic with a finger, and when it first runs it works perfectly.

    Board had all the PIA (6821) replaced, new sockets, new ram, new eproms, problem was the same before all this work.

    When using Leons test rom, everything seems to be in order.
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  • Acid damage does not look so bad but repair damage worse. Seems someone did shotgun it instead of checking what waas actually broken.

    10 blinks is U27 rom failure. So I would first inspect the rom socket. The actual error might actually something else. I would first remove the U41 and U42 sockets clean up and measure continuity. Then put machine pin sockets in and make sure no old desoldered PIAs are used.. I see some discolored traced at the upper left edge of u41. usually this means traces there might be broken at a via or socket pin.

    Afterwards it is more guesswork. Can be anything but usually bad repairs. If a was a friend of mine I would tell him/her to buy a good used board. Probably takes a few hours to fix up if ever.

    If you have an eprom burner try Leons system 11 test rom on a bench with a PC power supply.

    FRG
    Technische- und Reparaturanfragen per pm ohne vorherigen Forumsthread werden nicht beantwortet.
  • frg wrote:

    Acid damage does not look so bad but repair damage worse. Seems someone did shotgun it instead of checking what waas actually broken.

    10 blinks is U27 rom failure. So I would first inspect the rom socket. The actual error might actually something else. I would first remove the U41 and U42 sockets clean up and measure continuity. Then put machine pin sockets in and make sure no old desoldered PIAs are used.. I see some discolored traced at the upper left edge of u41. usually this means traces there might be broken at a via or socket pin.

    Afterwards it is more guesswork. Can be anything but usually bad repairs. If a was a friend of mine I would tell him/her to buy a good used board. Probably takes a few hours to fix up if ever.

    If you have an eprom burner try Leons system 11 test rom on a bench with a PC power supply.

    FRG
    Thank you for the reply.

    Its the Blanking LED that blinks 10 times, not the diagnostic, diagnostic led blinks 60 times, sockets are new, not my work, but the owner of the board, the reset circuit was repaired by a locale arcade guy (Very bad job, but it does reset as it should)

    The discolored traces are checked, and found okay, there was one broken, that is fixed with a jumper on the backside of the pcb, board is on the bench, using my lab power supply, set to 5 volts, and a jumper from 5 volt to zr1, leons test rom works fine in the board, no problems, PIA's and CPU' is checked using logic probe, and scope.

    A bad repair is quite possible, its just funny that sometimes the board will boot and run if touching the legs on a IC softly.
  • Hi,
    I've checked my CPU-board. On my board, the trace to pin 21 at U41 was broken. This is the R/W signal, that tells the PIA the direction of the data. The PIA didn't switch so I think the CPU tries testing the PIAs 60 times bevor it stops. One PIA didn't answer well. It is the same pin at all PIAs. Because your board works when pushing it, I think about a bad contact at one of the PIAs Pin 21. As Pin 21 at U41 is in your acid region, it may have a broken soldered point below the socket. But it also could be one of the other PIAs.
    I would check this first and after that the whole R/W traces back to the CPU-chip.

    Regards André
    Alive and kicking
  • > A bad repair is quite possible, its just funny that sometimes the board will boot and run if touching the legs on a IC softly.

    That is unfortunately quite typical for badly repaired acid damage. Also cheap sockets instead of machine sockets were used and you can't visually inspect traces when using them.

    Without a scope it might be impossible to find the problem. You can try Leons System 11 test rom to track this down further but you at least need a logic problem.

    Unfortunately to repair this properly every replaced socket and every ic not replaced but visibly acid damaged must go and traces reinspected then. I usually clean up and use a flashlight shining thru the pcb zhrn. Traces between two pins of the pias and also the connections directly at the pins are mostly affected.

    FRG
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  • #5

    Thank you for the reply, i pulled the sockets on U41 and U42 today just to check the traces, everything looks okay, there was on broken trace, but it was repaired on the back of the PCB.

    #6

    Ive got a scope, and a logic probe, so no problem there, testing says R/W is not pulsing, and touching pin 24/25 on the PIA's makes the board boot. (R/W does pulse when the board boots)
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  • Doesn't look so bad. 3 places I would check first. Trace near Pin 1 of U42 at the right. Pin 16 of U41 and the 7407. Seems to be a lot of gunk under it. This must go. Also check the other 74xx for gunk.
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    Technische- und Reparaturanfragen per pm ohne vorherigen Forumsthread werden nicht beantwortet.
  • It is not possible unless there is a near short with the lamp voltage or the 12V somewhere. Unlikely. Did you use a scope? Meter might show gibberish on the pulsed outputs.

    FRG
    Technische- und Reparaturanfragen per pm ohne vorherigen Forumsthread werden nicht beantwortet.
  • Only 5 volt is connected to the PCB.

    I am guessing maybe the meter is lying to me, scope is saying around 5 volt pr div, signal just looks noisy, logic probe on the same pin just shows high, no pulsing.

    EDIT: Bleh scrap that, it was the powersupply i was using to power the board that was making noise, after switching to a computer powersupply board no longer can be tricked into starting using a finger on the PIA trick.
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