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(Topic ID: 230519)

System 7 test rom RAM tests

By zacaj

1 year ago

Topic Stats

  • 10 posts
  • 4 Pinsiders participating
  • Latest reply 1 year ago by OHMI_Arcade
  • Topic is favorited by 3 Pinsiders


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    #2 1 year ago
    Quoted from zacaj:

    Trying to get a system 7 mpu booting, and I'm getting various 'bad RAM' readings.
    Leon's test rom locks the leds on immediately, but does not display 1,2, or 3 (which according to it should). Two leds no flashes indicates the IC13 RAM is bad.
    Andre's test rom blinks on 2 and 3, signifying that IC16 and IC19 are bad. Doesn't blink on 1 (IC13).
    Usually I find these tests pretty good on system 3-6 games, but I've never had a system 7 ram issue before. My confusion lies in the fact that IC13 and IC16 are different on system 3-6 vs system 7. on 3-6 they're the lower halves of the first 255 bytes of ram. on system 7 they each span the whole 255 bytes but each are only four bits. Both these test roms claim to work for system 3-7, so how can you tell which RAM on a system 7 is actually bad? It seems like if it just scans the full bytes (like it would for system 3-6) then it wouldn't know which chip it was that caused the error? A look at the source code for Andre's seems to read like it only scans full bytes, and thus won't produce accurate results on a system 7, but I may be misunderstanding...
    Can anyone confirm how to read these?
    Would marco's rom work better? I've never used it
    Is the system 7 self test more reliable than the system 3-6?

    The 2114 RAM are only four bit wide parts.... but they are longer. 6810 chips are eight bit wide, but shorter in length.

    Think of both the 2114 chips to be in the same address space, basically same chip. Then they combine the two 6810s together to get one long chip. Its like the cut width in half and then made it twice as long....

    Because of this i'd expect odd results from RAM tests for system 7. Either 2114 being bad should result in Andre's or Leon's test to repair fail at BOTH spots if I am thinking about it right.

    #4 1 year ago
    Quoted from zacaj:

    Thats what I would expect for a system 3-6 test being used in a system 6, but both my roms specifically say they support system 7? And Andres is saying one 2114 is good and one is bad?

    Instead of an entire bad chip it could just be detecting one or a couple bad bits somewhere and it plots out the location based on sys 3-6 layout which may not match system 7.

    Andre's ROM has no way to detect system 3-6 vs sys 7. I am going to assume the RAM tests are based on the layout of system 3-6 games which isnt going to line up properly to system 7.

    I'd honestly pull the most suspect chip out and test it in a RAM tester than do the other other if the first one pulled wasnt the bad RAM.

    #6 1 year ago
    Quoted from zacaj:

    None of the rams on any of my system 7s are socketed, so I can't test. Going to just have to remove and socket one by one, and have new rams on standby
    Or maybe I'll just write a system 7 ram test rom...

    Try the real sys 7 flipper roms. As long as it boots up somewhat I'd trust that ram test more than leon or Andre

    #8 1 year ago
    Quoted from zacaj:

    So those are more reliable? I've heard that the sys3-6 ones can't really be trusted. I tried them and got a 2, which again points to one of the RAMs

    I disagree with people that say the original RAM tests are unreliable. I find them to be better than the test ROMs which often give false reports and then there sys 3-6 vs 7 memory mapping also confuses it.

    The caveat is the cpu can't be locked up and is able to read the flipper ROMs. People get confused by erroneous LED behavior when the CPU is locked up and they go down wrong repair paths because of it. That is why the built in tests gets a bad wrap.

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