(Topic ID: 230002)

Tech Help: System 80b mpu got a bad spike of voltage, what to suspect?


By shacklersrevenge

6 months ago



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  • 11 posts
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  • Latest reply 6 months ago by G-P-E
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    #1 6 months ago

    I have a refurbished MPU from a Bounty Hunter. Problem is, the voltage went out of whack and it won't boot anymore, it's dead, so I'm suspecting it knocked out maybe the 6502 at U1? - EDIT- I’ve taken the 6502 out of my Haunted house and put the bounty hunter one in it, to determine 6502 is not the issue.

    What is usually fried or suspect in the path of a ''floating'' power supply? I do not have a logic probe, though there are really only a few chips around that +5 entry point.

    Any help is appreciated,
    thanks, James

    #2 6 months ago

    Does anyone know if these two blue jumpers are correct on the piggy back board?

    image (resized).jpg
    #3 6 months ago

    If the board received a higher voltage than 5V then potentially every chip on the board could be fried.

    In a situation like this there is never any "usual problem" - it's a matter of tracking down the damaged parts. Very complex and time consuming job most times.

    #4 6 months ago
    Quoted from shacklersrevenge:

    Does anyone know if these two blue jumpers are correct on the piggy back board?
    [quoted image]

    That looks like it may be the GPE replacement piggyback board: https://www.greatplainselectronics.com/proddetail.asp?prod=140-101

    If you go to that page, there’s a link for the documentation for that board which shows the jumper configurations.

    #5 6 months ago
    Quoted from Homepin:

    If the board received a higher voltage than 5V then potentially every chip on the board could be fried.
    In a situation like this there is never any "usual problem" - it's a matter of tracking down the damaged parts. Very complex and time consuming job most times.

    6502 is fine, z1, z36 and Z5 are fine, eprom is fine

    #6 6 months ago
    Quoted from pincity:

    That looks like it may be the GPE replacement piggyback board: https://www.greatplainselectronics.com/proddetail.asp?prod=140-101
    If you go to that page, there’s a link for the documentation for that board which shows the jumper configurations.

    Thank you, that was exactly what I was looking for, looks to be jumpered correctly.

    #7 6 months ago

    I have had to fix numerous bally MPUs where 12v or worse gets onto the 5v rail. Usually The CPU, RAM, interface adapters, and all the 7400 series chips are dead. The 4000 series parts usually live. Sometimes you get lucky and one part will go low resistance and blow the fuse / shutdown the v-reg before much else goes bad.

    I'd start with checking anything in a socket you can pull out and test in another board/rom burner to get an idea of the damage.

    #8 6 months ago
    Quoted from barakandl:

    I have had to fix numerous bally MPUs where 12v or worse gets onto the 5v rail. Usually The CPU, RAM, interface adapters, and all the 7400 series chips are dead. The 4000 series parts usually live. Sometimes you get lucky and one part will go low resistance and blow the fuse / shutdown the v-reg before much else goes bad.
    I'd start with checking anything in a socket you can pull out and test in another board/rom burner to get an idea of the damage.

    I've been putting in sockets and removing chips/replacing with good chips, but no change. So far, z5, z36, z4, z1, u1 (6502), u5, all test fine when I throw them in a good board and power up the other game (Haunted House)

    The game rom is fine, I had it in a swemmer board to test.

    I mean, after all that, there's not a ton for it not to boot. There's the sn74hcto4n next to the game eprom on the piggy back board which I do not have a spare of, and I'm starting to suspect, u4 and u6 (both 6532) and chips z7, z8, z9 and z10 in the left corner of the board. Am I missing something crucial? I have +5 steady, and I used a swemmer board with the eprom without issue in it last year, so the ''system'' is fine.

    I had Chris Hibler service the board a couple years back, and with maybe 5 hours of game time on it, one day just failed to boot up. I had suspected a voltage spike, but maybe not. Any ideas?

    Thanks, James

    #9 6 months ago

    For the 74HCT04 -- try a 74LS04 if you have one. Not at all critical regarding brand or HCT versus LS.

    For replacing IC's - I would have started with the cheaper parts such as the 74xx series parts.
    As mentioned by BarakandI - the 74xx series parts (including 74HCT04) have max voltages of 7V, anything above that can take them out. 4000 series are more tolerant and can work up to about 15.

    All the decode logic (Z9, Z10, Z12, Z7, Z8) as well as Z2 and Z3 are suspect. Plus the stuff hanging off U4 through U6 would be equally suspect.
    Z1, Z4 and Z36 would have been less concerning.

    2 weeks later
    #10 6 months ago
    Quoted from G-P-E:

    For the 74HCT04 -- try a 74LS04 if you have one. Not at all critical regarding brand or HCT versus LS.
    For replacing IC's - I would have started with the cheaper parts such as the 74xx series parts.
    As mentioned by BarakandI - the 74xx series parts (including 74HCT04) have max voltages of 7V, anything above that can take them out. 4000 series are more tolerant and can work up to about 15.
    All the decode logic (Z9, Z10, Z12, Z7, Z8) as well as Z2 and Z3 are suspect. Plus the stuff hanging off U4 through U6 would be equally suspect.
    Z1, Z4 and Z36 would have been less concerning.

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    #11 6 months ago

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