05 July 2019, 17:50 | #1 |
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A500 Rev6 fries any memory expansion
Hi all,
I've just found a fully working A500 Rev6 but the problem is that it fries any memory expansion I connect to it quickly Actually, it burns the four 514256 RAM chips on the card that smells very bad How can I fix it? what to check? |
05 July 2019, 18:01 | #2 |
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The computer works otherwise? ;-)
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05 July 2019, 18:05 | #3 |
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05 July 2019, 18:06 | #4 |
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Can you do a mockup installation of the memory card and take a photo. Please don't power up the machine.
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05 July 2019, 18:14 | #5 |
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05 July 2019, 18:15 | #6 |
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Looks fine to me. How many mem expansions have you blown with the machine?
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05 July 2019, 18:23 | #7 |
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Two till now
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08 July 2019, 17:44 | #8 |
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08 July 2019, 20:02 | #9 |
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Have you checked for shorts? maybe the isolation material between the board and metal shielding has failed in some way and 5V is going into other pins?
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09 July 2019, 08:24 | #10 |
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I traced the 5V but it had no contact with other pins.
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09 July 2019, 11:34 | #11 |
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Have you checked the 12V lines as well?
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09 July 2019, 18:35 | #12 |
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Yes, those are isolated.
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10 July 2019, 00:51 | #13 |
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Are the expansions you've tried the same model and from the same source? could it be fake chips? I noticed they look a bit scuffed and no markings? I'd still try separating the the board from the metal shielding to see if it helps.
I've also noticed a bit of yellow where the connector is soldered to the A500 motherboard, is it excess flux? previous owner possibly did a repair and didn't bother to clean? Last edited by Mick; 10 July 2019 at 01:26. |
10 July 2019, 13:41 | #14 |
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Since you have a desoldered board - what is the voltage on the 5V pad for the IC?
And how does the shield look on the underside of the motherboard below the expansion connector? If someone soldered on the connector with the shield+insulation in place, it could have melted the insulation and created an intermittent short (so you wouldn't be able to measure it all the time). If the IC was already fried, it could get hot simply from the current running through the other pins. |
11 July 2019, 09:09 | #15 | |
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Quote:
After replacing the chips: |
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11 July 2019, 09:31 | #16 |
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Haven’t seen a A501 card like that before. Did it have a battery on it?
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11 July 2019, 10:32 | #17 |
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Looks like a third party/homebrew card, not an official Commodore one.
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11 July 2019, 15:58 | #18 |
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11 July 2019, 16:39 | #19 |
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11 July 2019, 18:01 | #20 |
CaptainM68K-SPS France
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