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Galaga Repair

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jonhughes View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jonhughes Quote  Post ReplyReply Direct Link To This Post Topic: Galaga Repair
    Posted: 22 Sep 2017 at 9:24pm
Did this one for Andy (U72)

Board had numerous faults. Board would not boot, kept re-setting or giving RAM error (to bottom board at 2H I think). Swapped in an known working bottom board and got same error so knew that was BS.

Here's the complete run down:

1) Replaced socket at 2L and re-attached loosening legs to 06XX chip
2) ROM 7 at 3E bad and replaced, Fujitsu 2732 to blame for that one.

This fixed the top board. Next the bottom board.

3) Replaced 2200 ohm resistor pack at RM4 had been bent completely over which knackered it
4) Replaced socket at 4M for 05XX (star field chip)


Really bad contacts.

5) Dug out 6M 6148 RAM chip socket after finding 2 broken traces on the removed sprite RAM - one trace iffy beneath so patched a line in. Someone had ripped out four 8147 RAM (6J to 6M) and replaced with a single 6148 at 6H but did a really bad job of it.


6) Decided to replace the other 4 custom sockets to ensure longevity of the PCB, no point getting the board back a week or two later

Now booting but to a screen with odd blue lines



Blue lines would disappear upon manipulation of the harness. Cleaned edge harness and did various other things which appeared to switch lines on and off. Left this running for a long while and all lines disappeared. Knew this was now heat related - this is a nightmare and one of the most PITA faults to track down.

However, on a hunch from another weird fault I've had with a different PCB decided to clean and reseat all the 2114 RAMs between 3E and 3L and moved their positions up one. Fault almost disappeared. Pulled chips again and noticed some of the legs were not completely straight - straightened the lot (making very sure) and all blue lines disappear


Now done - Happy days.



Edited by jonhughes - 22 Sep 2017 at 9:27pm
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Hurray Banana View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurray Banana Quote  Post ReplyReply Direct Link To This Post Posted: 23 Sep 2017 at 7:00am
great fix john
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Judder View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Judder Quote  Post ReplyReply Direct Link To This Post Posted: 23 Sep 2017 at 11:46am
Nice fix and got to love a bit of Galaga (was playing ours yesterday)

This is one of the best thing about the muti-part boards, if you have two sets of them and one known worker then you can swap bottom to top etc. to narrow down your faults Thumbs Up
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jonhughes View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jonhughes Quote  Post ReplyReply Direct Link To This Post Posted: 23 Sep 2017 at 1:42pm
Originally posted by Judder Judder wrote:

Nice fix and got to love a bit of Galaga (was playing ours yesterday)

This is one of the best thing about the muti-part boards, if you have two sets of them and one known worker then you can swap bottom to top etc. to narrow down your faults Thumbs Up

Correct, when the test result is showing you have a RAM fault that is on the bottom board and it's actually the top board to blame for the fault (and there's nothing wrong with the RAM) you can waste a whole lot of time chasing a fault on the wrong board. It would be the natural thing to do to home in on that RAM chip.

I've had stacks of false positive results from various things including those test error messages - I guess it's all part of the joy.
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