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Robotrontechnik-Forum » Technische Diskussionen » A5120 fix - help needed » Themenansicht

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000
18.08.2025, 15:21 Uhr
RetroNora

Hello,
I have been trying to fix my Robotron A5120.
The symptoms are:
- with normal boot ROM it seeks all three drives, looking at YT videos this is what it should do. But if I insert a floppy with boot image the drive LED is light, the motor spins but the heads does not step, even if before (with unplugged system) moved by hand. There is no data comming from the floppy drive (measured on the floppy connector with oscilloscope.

I have tried to use a RAM test ROM from felge site (http://felgentreu.spdns.org/dokuwiki/doku.php?id=robotron:kartensaetze:k1520:k2526).

The output looks like this:

If I understand it right it suggest that the last 2K of RAM are faulty.

The RAM card on my A5120 is K3526 with 64K of DRAM. I have checked the 4th bank of the RAM card and all of them are tested to be good.

If I take out the RAM from last bank, the last 2K also seems 'bad' rather then empty like other addresses from the 4th bank.

I have tested the 8212 that connect the address lines to 4th bank on the card and on CPU board.

Any ideas what is going on?

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001
18.08.2025, 15:32 Uhr
Rüdiger
Administrator

Zitat:

RetroNora schrieb
If I understand it right it suggest that the last 2K of RAM are faulty.

No, this is video RAM: it cannot be tested, otherwise you would loose screen content.

You are using a strange character set: likely the "ó" should be "@", which means correct Kilobyte. And we see all Kilobytes are correct.

If your A520 attached the floppy drives, it means the RAM has no hard damages.
The problem can be also at ZVE card or at AFS card.
Or a card is not plugged into the correct slot.
--
Kernel panic: Out of swap space.

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002
18.08.2025, 15:55 Uhr
RetroNora

Thanks, the ó is because my A5120 has a Polish charset.

I think the cards are in correct order since I got the computer with warranty seal around them. It goes (from floppy cage):
1. RAM,
2. Floppy controller,
3. IFSS card,
4. ZVE,
5. Video Board,
6. empty
7. another RAM board.

I have already replaced three 8216 on CPU board and one on Floppy controller, also one 7408 on the floppy controller. Before it did not seek the floppies at boot.

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003
18.08.2025, 16:10 Uhr
Rüdiger
Administrator

What is "another RAM board"?
--
Kernel panic: Out of swap space.

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004
18.08.2025, 16:15 Uhr
RetroNora

062-8471

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005
18.08.2025, 16:22 Uhr
Rüdiger
Administrator

You can temporary remove 062-8471, to exclude the influence of this board.

It makes no sense to replace IC's blindly.
Go with your boards to somebody owning a functional A5120 and check, wich board is faulty.
--
Kernel panic: Out of swap space.

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006
18.08.2025, 16:48 Uhr
RetroNora

Oh if it was this easy, I do not know anyone like this

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007
18.08.2025, 17:13 Uhr
Rüdiger
Administrator

There are German hobbyists near the Polish border. And there are postal ways.
--
Kernel panic: Out of swap space.

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008
18.08.2025, 18:03 Uhr
RetroNora

Well, now at least I know I should not focus on the memory.

After some measurements I guess the control PIO or the control signals for the PIO are bad. Since the /step signal is not generated, the /index signal arrives at PIO.
Also I don't think that this is how the /step-direction signal should look like:

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