exxos's Atari, Amiga & retro forum

Posted: **04 Mar 2026 13:54**

Hello there ! (sorry for my average English)

I've an issue on the acsi port on a 1040 ste /Tos 2.06 /RAM 2Mo /Good DMA chip C398739-001A / No issues with floppy drive it can format, copy, read, well / PSU recaped few month ago with normal voltage on the outputs 11,8V and 4,95V.

The problem is that my acsi2stm are not recognized (no banner boot), and the activity orange led stays always ON when atari is powered with or without sd card inserted. (Normaly it should be off when atari is powered.)

I tried with 2 differents acsi2stm "black pill" that are working fine on another 1040 ste, that's why I suspect an issue on the acsi port.

I've looked at the 1040ste shematic and the pdf "Atari ACSI/DMA Integration guide", then I mesured voltage on each acsi port pin
(atari powered, on the desktop, and no acsi2stm plugged to the acsi port)

Acsi pin 1 = Data bus 0, TTL levels, active high / Voltage mesured = 3,42V
Acsi pin 2 = Data bus 1, TTL levels, active high / Voltage mesured = 3,43V
Acsi pin 3 = Data bus 2, TTL levels, active high / Voltage mesured = 3,45V
Acsi pin 4 = Data bus 3, TTL levels, active high / Voltage mesured = 3,40V
Acsi pin 5 = Data bus 4, TTL levels, active high / Voltage mesured = 3,42V
Acsi pin 6 = Data bus 5, TTL levels, active high / Voltage mesured = 3,42V
Acsi pin 7 = Data bus 6, TTL levels, active high / Voltage mesured = 3,44V
Acsi pin 8 = Data bus 7, TTL levels, active high / Voltage mesured = 3,40V
Acsi pin 9 = HDCS - Chip Select, TTL levels, active low / Voltage mesured = 3,56V
Acsi pin 10 = XHDINT - Interrupt Request, TTL levels, active low / Voltage mesured = 4,90V
Acsi pin 11 = Ground / Voltage mesured = 0 V
Acsi pin 12 = RESET, TTL levels, active low / Voltage mesured = 3,56V
Acsi pin 13 = Ground / Voltage mesured = 0 V
Acsi pin 14 = HDACK - Acknoledge, TTL levels, active low / Voltage mesured = 3,56V
Acsi pin 15 = Ground / Voltage mesured = 0 V
Acsi pin 16 = A0 - Adress 1, TTL levels, active high / Voltage mesured = 3,56V
Acsi pin 17 = Ground / Voltage mesured = 0 V
Acsi pin 18 = R/W - Read/Write, TTL levels, high=read / Voltage mesured = 3,57V
Acsi pin 19 = HDRQ - Data Request, TTL levels, active low / Voltage mesured = 0 V

I'am not enough skilled to interpret these mesures, I have no oscilloscope nor logic probe, nor diagnostic cartdridge. Does a diagnostic software could help me ? Wich one ?

According to the 1040ste schematic, Pin 19 is linked to U305 a 7406N (hex inverter buffers/drivers), I got one in spare so I replaced it with no success the issue is still there.

Any idea ?

Many thanks !

Fred

20260304_150834.jpg

Posted: **04 Mar 2026 17:51**

Even if you have the DMA with the right reference, it can happen that you also need to replace the 68000 for an 68HC000P8 ou P10 (QFP model, not the DIP-64 model).

I own 3 STE : 2x 520 STE (one with 1mb, one with 4mb), and 1x 1040 STE. I changed the DMA chip on the 1040 STE and one 520 STE. It did not solved the problem. I had to follow Exxos advice about the CPU replacement.

Note also that your 1040 STE is a 1989 model. Atari fixed definitively the "DMA problem" on STE's made around september/October 1990. So your computer is very probably like my own STEs. STE made and sold in 1991 are free of any Hard Drive/DMA problems.

(The original 68000, is sucking quite a good chunk of current, is heating up, is pumping a lot on the +5V, and age badly with time).

I bought 2x 68HC000, and it solved instantly the problem. The fact is that this CPU uses way less current, doesn't heat up, and the best : generate less noise on the PSU, doesn't hit the 5V Regulator like crazy, and enhance sometimes the DMA/ACSI stability.

Personally, that's what i would do. Count around 20UKP if you live in UK per CPU.

Posted: **04 Mar 2026 19:28**

It might be worth looking at the ACSI connector too. A few montage I ran into an issue with a 520ST and it was actually one of the ACSI connector’s pin which was pushed inside. From outside it looked ok, from inside the metal part was clearly pushed outside of the socket (and shorting to other pins).
A lot of ACSI2STM comes with square pins and this doesn’t do well with the old connectors.

Posted: **04 Mar 2026 20:44**

- Many thanks for your advices, you convinced me to try a new cpu. However according to the schematic i would suspect first (u307) 74ls244 or (u302) 74ls245 or in the worst case the glue/blitter chip itself as acsi pin 10 is directly linked on it. ( I ve ever checked all the resitances linked to the acsi port) . Does all these mesures around 3,40V Are normal, I thought high TTL level would be around 5V ?
Next week I'll manage to compare these voltage on my friend's 1040ste with working acsi port.

- A short between pins inside the acsi port is tricky ! So I've just checked resistance between acsi port solders under the motherboard and all looks fine there...

- Of course contacts have been cleaned inside acsi port

Posted: **04 Mar 2026 20:44**

Sbn31 wrote: 04 Mar 2026 13:54 Hello there ! (sorry for my average English)

I've an issue on the acsi port on a 1040 ste /Tos 2.06 /RAM 2Mo /Good DMA chip C398739-001A / No issues with floppy drive it can format, copy, read, well / PSU recaped few month ago with normal voltage on the outputs 11,8V and 4,95V.

The problem is that my acsi2stm are not recognized (no banner boot), and the activity orange led stays always ON when atari is powered with or without sd card inserted. (Normaly it should be off when atari is powered.)

I tried with 2 differents acsi2stm "black pill" that are working fine on another 1040 ste, that's why I suspect an issue on the acsi port.

I've looked at the 1040ste shematic and the pdf "Atari ACSI/DMA Integration guide", then I mesured voltage on each acsi port pin
(atari powered, on the desktop, and no acsi2stm plugged to the acsi port)

Acsi pin 1 = Data bus 0, TTL levels, active high / Voltage mesured = 3,42V
Acsi pin 2 = Data bus 1, TTL levels, active high / Voltage mesured = 3,43V
Acsi pin 3 = Data bus 2, TTL levels, active high / Voltage mesured = 3,45V
Acsi pin 4 = Data bus 3, TTL levels, active high / Voltage mesured = 3,40V
Acsi pin 5 = Data bus 4, TTL levels, active high / Voltage mesured = 3,42V
Acsi pin 6 = Data bus 5, TTL levels, active high / Voltage mesured = 3,42V
Acsi pin 7 = Data bus 6, TTL levels, active high / Voltage mesured = 3,44V
Acsi pin 8 = Data bus 7, TTL levels, active high / Voltage mesured = 3,40V
Acsi pin 9 = HDCS - Chip Select, TTL levels, active low / Voltage mesured = 3,56V
Acsi pin 10 = XHDINT - Interrupt Request, TTL levels, active low / Voltage mesured = 4,90V
Acsi pin 11 = Ground / Voltage mesured = 0 V
Acsi pin 12 = RESET, TTL levels, active low / Voltage mesured = 3,56V
Acsi pin 13 = Ground / Voltage mesured = 0 V
Acsi pin 14 = HDACK - Acknoledge, TTL levels, active low / Voltage mesured = 3,56V
Acsi pin 15 = Ground / Voltage mesured = 0 V
Acsi pin 16 = A0 - Adress 1, TTL levels, active high / Voltage mesured = 3,56V
Acsi pin 17 = Ground / Voltage mesured = 0 V
Acsi pin 18 = R/W - Read/Write, TTL levels, high=read / Voltage mesured = 3,57V
Acsi pin 19 = HDRQ - Data Request, TTL levels, active low / Voltage mesured = 0 V

I'am not enough skilled to interpret these mesures, I have no oscilloscope nor logic probe, nor diagnostic cartdridge. Does a diagnostic software could help me ? Wich one ?

According to the 1040ste schematic, Pin 19 is linked to U305 a 7406N (hex inverter buffers/drivers), I got one in spare so I replaced it with no success the issue is still there.

Any idea ?

Many thanks !

Fred20260304_150834.jpg

Also worth scooshing the socket with contact cleaner.

exxos's Atari, Amiga & retro forum

1040 STE acsi/dma port issue

1040 STE acsi/dma port issue

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