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Robotrontechnik-Forum » Technische Diskussionen » Fixing K8915 » Themenansicht

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000
31.05.2026, 08:51 Uhr
RetroNora

Hello,
I'm fixing my K8915 (the version listed as 5,25 inch version 1, with K2521 CPU board and K7634 keyboard).

After fixing the video board I'm getting Diagnostic Key71 message.

Is this a ram error?

Thanks in advance!

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001
31.05.2026, 12:39 Uhr
DKt

Hi Nora,

no, Errorcode 71 usually means that keyboard is not connected.

The Power On Self Test of K8915 has several Steps:
ROM
RAM
RAZ
KEY
CTC
SIO
In your case it stops at KEY with errorcode 71.

Is the keyboard connected properly?
The keyboard port is an 2*13 PIN connector on ATS board (012-6710 or 012-6720)

Greetings, Dirk

Dieser Beitrag wurde am 31.05.2026 um 12:40 Uhr von DKt editiert.

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002
31.05.2026, 13:44 Uhr
RetroNora

Thanks for your answer,
The keyboard is connected.
At power on sometimes the beeper in keyboard beeps twice, sometimes once and sometimes it is a continous beep.

But at least now I know on what part to focus.

Greetings
Filip

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003
31.05.2026, 14:02 Uhr
DKt

Hi Filip,

do you have another ATS or another keyboard?

But it sounds like keyboard itself is not initiaizing correctly. It contains a separate U880 CPU and a firmware ROM.

Btw: the frame where the CRT is mounted does not look like the display unit of 8915. Is ist an external screen?

The other strange thing is: The pattern shown on screen look like a RAM Error. But the main RAM area check must be ok, because it is performed before keyboard check.

Greetings, Dirk

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004
31.05.2026, 14:23 Uhr
RetroNora

I do not have any other keyboard or ats board.
Will look around at the keyboard and ATS board to see if I see any obvious issues.

The screen looks like RAM error indeed.

Yes, this is an external screen - monitor with signal feed throu K8915 video to CVBS resistor network adapter.
My K8915 arrived with smashed CRT neck, first I want to make it work, later finish the cosmetics and fix crt.

Greetings,
Filip

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005
03.06.2026, 09:29 Uhr
RetroNora

Hello,

I was able to get rid of the KEY error by replacing one of 8212 ICs on the keyboard board (DB5 was stuck high), now I am getting CTC 8Z error.
Do You know if the CTC check is about the CTC on the ATS or the ZRE or both boards?

Also, if I press 'ENTER' on the keyboard the computer proceeds to boot.

The garbage one can see on the screen pic I have posted seems to be some error with video memory not being cleared at initialization.

If I press 'ENTER' enough times the screen get's filled with boot messages and the garbage dissappears.

Greetings
Filip

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006
05.06.2026, 09:23 Uhr
RetroNora

Hello,
After replacing one 2114 on the video board the screen looks correct.
Now only the CTC error is to be solved.

Greetings
Filip

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007
05.06.2026, 14:15 Uhr
Rüdiger
Administrator

Zitat:

RetroNora schrieb
Do You know if the CTC check is about the CTC on the ATS or the ZRE or both boards?

Likely ZRE.
--
Kernel panic: Out of swap space.

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008
06.06.2026, 19:15 Uhr
DKt

Hi Filip,
I can confirm, that CTC81 belongs to ZRE CTC.
CTC82 would be error on ATS CTC.

If I see it correctly, for testing the CTC will be programmed, and an interrupt will be expected before a wait loop expires.

Greetings, Dirk

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