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Old 29 June 2020, 17:09   #1
marioboy
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Hooooo A500+ motherboard - black screen

I bought this motherboard of A500+ several years ago. It have been shipped only with 512k RAM card.



Couple days ago I bought power supply, and finally had chance to power up this board. Power supply came with cut-off plug, but I checked voltages and put each cable into power port, according to pinout scheme from wiki (I know, it's hillbilly level of electronics, but it does the work )



Black screen - that's all. No matter what did I try - there is signal via AV port, but no image, only black screen.

I am complete noob about Amiga, never used it, that's why have no idea what to do.

About the motherboard:
visually it has no damage, board looks very great. There are missing elements at "clock" and "battery" section, but I have no idea is it revision or indeed elements have been removed - there are no any signs that this board have been messed around with.



There are something with Fat Agnus: 1) There is some element soldered on bottom side of board; 2) socket has plastic missing on one of the corners

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Old 29 June 2020, 17:24   #2
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Looks like a rev 8A board that was used in an A500 case - since there is no battery and RTC onboard.

The battery on the memory expansion unit needs removing. Although, admittedly, it does look in good condition.

Try to boot up without the memory expansion connection And reseat and clean all the socketed chips and sockets.

The issue with the Fat Agnus socket needs to looked at and probably a new socket is needed. Check that the socket pin on the corner where it is broken is making contact with the Fat Agnus pin.

I'm not sure what the mod is, and doing, on pin 40 (CCK) of Fat Agnus.
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Old 29 June 2020, 18:47   #3
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Now it's white screen

Quote:
Originally Posted by solarmon View Post
Try to boot up without the memory expansion connection And reseat and clean all the socketed chips and sockets.


I did as you advised to me, and noticed corrosion at CPU socket. When I tried to boot without CPU at all I saw same black screen. Maybe this is a root cause?
I did brushed socket with some alcohol slightly, left to dry and put chip back.
Some progress - now it's white/light greyish screen. But nothing else, again.

Also, trying to turn motherboard with/without RAM card made no difference
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Old 29 June 2020, 19:40   #4
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I assume that is a picture before you cleaned it up? There's quite a lot of corrosion/oxidation.

What are the other sockets like, especially the Kickstart ROM socket.

You also need to inspect the chip pins. Use something abrasice like sand paper or a fine file to clean any corrosion/oxidation off it.

A tip is when you put the chips back, push it in very slightly and then move the whole chip back and forth in the socket so that the chip legs wipe against the socket blades. Then push it all the way in. Try doing this several times as the more you do it the cleaner it will get.
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Old 29 June 2020, 20:23   #5
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Quote:
Originally Posted by solarmon View Post
I'm not sure what the mod is, and doing, on pin 40 (CCK) of Fat Agnus.
This is required for the Voltage Back Bias (VBB) versions of Agnus.
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Old 29 June 2020, 20:37   #6
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Quote:
Originally Posted by solarmon View Post
I assume that is a picture before you cleaned it up? There's quite a lot of corrosion/oxidation.

What are the other sockets like, especially the Kickstart ROM socket.

You also need to inspect the chip pins. Use something abrasice like sand paper or a fine file to clean any corrosion/oxidation off it.
Yes, it was before.

Chip is ok, I did cleaned as you said. Also, I cleaned all other DIP sockets, though non of them had corrosion. Unfortunately screen is same, no signs of life.
ROM socket is clean, same as chip, but I recleaned both.
I tried power on without ROM chip - screen was black. With it - white.
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Old 29 June 2020, 20:45   #7
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Do you have a multimeter to test continuity of the traces? A logic probe will also be useful in this situation.

You can use amigapcb.org to find out where the traces are and where they should go.

One last thing to try is to swap the CIA chips to see if that changes anything.
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Old 29 June 2020, 20:54   #8
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I do have multimeter
Do you mean to check every trace of every chip?

I did tried to swap CIA chips, and it changed nothing
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Old 29 June 2020, 21:02   #9
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Yes, that seems to be the direction we are going.

If you have another A500(+) then you can check the chips between the two machines.

Can you check and show all the jumpers on your board - the picture you have provided suggest they have been modified.

I'm not familiar with what the jumper settings are done for a rev 8A board that is downgraded to be used as an A500 board, but somebody else might be able to help.

It could be that the board has been modded and those jumpers are stopping it from booting.
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Old 29 June 2020, 21:18   #10
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Quote:
Originally Posted by solarmon View Post
I'm not familiar with what the jumper settings are done for a rev 8A board that is downgraded to be used as an A500 board, but somebody else might be able to help.
See here: http://eab.abime.net/showthread.php?t=77705
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Old 29 June 2020, 21:53   #11
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Thanks @amigasith!

A very quick glance seems to suggest those jumpers are correct, so it can't be because of those.

It looks like you need to check the traces and test the chips if you can.

Maybe a DiagROM may also be required.
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Old 29 June 2020, 22:21   #12
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Quote:
Originally Posted by solarmon View Post
If you have another A500(+) then you can check the chips between the two machines.
Unfortunately this board is only I have

Quote:
Originally Posted by solarmon View Post
Can you check and show all the jumpers on your board - the picture you have provided suggest they have been modified.

I did a picture of all jumpers, and comparison with pic from thread that @amigasith game shows, that they are seem to be in proper position. Just in case - also adding picture of other jumpers I managed to spot on a board




Quote:
Originally Posted by solarmon View Post

It looks like you need to check the traces and test the chips if you can.
Sorry for nooby question, but shal I simply test trace of each leg of each chip? Or shall I begin from something specific?

Quote:
Originally Posted by solarmon View Post

Maybe a DiagROM may also be required.
I will order this one - https://ebay.to/3ih9hB1
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Old 29 June 2020, 23:05   #13
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If it was my board I would start with the traces for the CPU and Kickstart ROM. However, without being able to confirm that the chips are actually OK, it may be a wasted effort.

Having the keyboard and floppy drive connected can also give other clues based on the LEDs and floppy drive behaviour.
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Old 01 July 2020, 16:08   #14
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Quote:
Originally Posted by solarmon View Post
...without being able to confirm that the chips are actually OK, it may be a wasted effort.
So, following advice regarding ROM and CPU check, I decided to order online Kickstart ROM, DiagROM and CPU.

I have a question regarding CPU. On the left is the one on my motherboard, and on the right - one I am planning to buy.

I don't really know what numbers on chips means.

Mine is:
MC68000P8
2C91E
QQTN9236


And online is:
MC68000P8
2C91E
QQAD9251


Will this CPU work if I will buy it and put in my A500+?

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Old 01 July 2020, 17:03   #15
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As long as the model number is suitable.

The last line I believe is the batch code for where/when it was made. The last four digits represent the date in the format YYWW, where YY is the year and WW is the week number, that is was made.
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Old 21 July 2020, 13:27   #16
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So, I have received DiagROM.
After installing the chip on the board, following is happening.

Screen is flashing for couple seconds:


After that these lines appearing, and bottom section of screen is flashing.



I assume that it may be either CPU malfunction or socket corrosion.
I am still expecting shipping of new CPU, so as soon as will get it will be able to know for sure.

I did tried to brush it with strong alcohol really hard, but it doesn't seem to help - pins on a socket still look greenish.

May somebody recommend me what should I use to clean corrosion of the CPU socket?
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Old 21 July 2020, 14:09   #17
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One tip to clean sockets is to use the chip pins themselves.

Put isopropyl alcohol in to the sockets then put the chip back on to it, push in slightly and push the chip back and forth so that the chip pins wipe/scrape against the socket blades. Keep slowly pushing the chip further in and pushing it back and forth until you cannot do it and further. Take the chip back out and try to soak up all the alcohol in the sockets - either using cotton buds or blowing it out with air.
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