Robotrontechnik-Forum

Registrieren || Einloggen || Hilfe/FAQ || Suche || Mitglieder || Home || Statistik || Kalender || Admins

Willkommen Gast!

Robotrontechnik-Forum » Technische Diskussionen » Fixing K8915 » Themenansicht

Autor

Thread - Seiten: -1-

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!

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

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.

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

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

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

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

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

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

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

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

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

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

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

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.

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

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

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

009
09.06.2026, 09:16 Uhr
RetroNora

Thanks.
ATS CTC seems to be the issue indeed.
It is not generating an interrupt.
I have checked and the IC itself is fine. None of the control signals for the CTC is stuck at any logic level so either it is not programmed correctly or it is not triggered to generate an interrupt.

Do you know what CTC channel is supposed to be the origin of the interrupt?

Greetings
Filip

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

010
09.06.2026, 11:11 Uhr
Dresdenboy

Hi Filip,

do you know the documents here?
https://www.tiffe.de/Robotron/K8915/Schaltungsunterlagen/

Best regards,
Matthias
--
___________________________________
Produktionen im Rahmen der "The Computer Art Community" (Demoszene): https://demozoo.org/sceners/64936/, YT-Kanal: https://www.youtube.com/@4lpha0ne/videos
Aktuelle Projekte: GDC-Analysen für Grafikeffekte u. Demo/Game-Framework, universelles BIC-Modul auf Pico-Basis, Packer mit sehr kleinem 6502-Dekompressor
HW: BIC, MSX2+, KC87, KC85/2-4, KCC, LC-80, PC1715, C64, C16, Plus/4, A500, A1200, Mega 65, µCs ...

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

011
09.06.2026, 11:18 Uhr
RetroNora

Hello,
I know them, sadly these are for later version of K8915, mine does not use these boards.

Regards
Filip

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

012
09.06.2026, 12:50 Uhr
Dresdenboy

Zitat:

RetroNora schrieb
Hello,
I know them, sadly these are for later version of K8915, mine does not use these boards.

Regards
Filip

OK, I see. I don't know about board revisions (LOL, just heard the same word in parallel in an interview I'm listening to). But would the CTC signal wirings have changed? The ATS board schematic is on p. 11.
--
___________________________________
Produktionen im Rahmen der "The Computer Art Community" (Demoszene): https://demozoo.org/sceners/64936/, YT-Kanal: https://www.youtube.com/@4lpha0ne/videos
Aktuelle Projekte: GDC-Analysen für Grafikeffekte u. Demo/Game-Framework, universelles BIC-Modul auf Pico-Basis, Packer mit sehr kleinem 6502-Dekompressor
HW: BIC, MSX2+, KC87, KC85/2-4, KCC, LC-80, PC1715, C64, C16, Plus/4, A500, A1200, Mega 65, µCs ...

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

013
09.06.2026, 12:58 Uhr
RetroNora

Well, I got different revision ATS board as well. Triggers are connected via jumpers.
On my board it seems that the channels 0-2 triggers are connected to ground, while trigger for channel 3 is connected to /UINT signal from keyboard connector.

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

014
09.06.2026, 17:08 Uhr
DKt

Hi Filip,

on ZRE CTC Channel 3 is used.
Address Range of ZRE CTC is 80h...83h
Port 83h (that means channel 3) will be programmed with the control word and the timing constant.

Controlword 0a7h = 1010 0111
1 - Interrupt enable
0 - Timer Mode
1 - Prescaler Value = 256
0 - Trigger falling edge
0 - automatic trigger when time constant is loaded
1 - Time constant follows
1 - Software Timer Reset
1 - Channel control word
Timing constant ZRE CTC = 0ch

ATS CTC: same controlword,
Timing constant ATS CTC = 18h

Greetings, Dirk

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

015
09.06.2026, 17:29 Uhr
DKt

Hi Filip,

boards must be inserted into the cage without a gap starting from the right end when you look from behind. There is an interrupt chain on pin 10 on the backplane. If there is a gap, the interrupt chain is broken.

From the right (near the screen) the board order -without any gap- is
ABS (012-6820)
ATS (012-6710)
OPS (045-8530)
ZRE (012-7100)
AFS (062-8390)
optional
OPS2 (045-8530)
ASL (062-8500)
or
ILA (045-8445)

Greetings, Dirk

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

016
10.06.2026, 13:19 Uhr
DKt

Hi Filip,

there is a wire wrap field on ZRE board for configuring the CTC.
It is documented this way:

x14:2-x15:2 /IEI

x10:1-x11:1 ZC/T02-CLK/TRG3
x10:2-x11:2 ZC/T01-CLK/TRG2
x10:3-x11:3 ZC/T00-CLK/TRG1
x10:4-x11:4 00 -CLK/TRG0

ZRE Documentation has gone out by email.

Greetings, Dirk

Dieser Beitrag wurde am 10.06.2026 um 13:22 Uhr von DKt editiert.

Profil || Private Nachricht || Suche

Zitatantwort || Editieren || Löschen

Seiten: -1- [ Technische Diskussionen ]