exxos's Atari, Amiga & retro forum

Posted: **20 Aug 2021 19:56**

Not sure i did it correctly, i think so. I hade one probe on AS and one probe on a address line. Then i had a trigger on AS and recorded 0.001s after it triggered. Went back to the beginning and took a screenshot.

So i hold reset, started recording, released the reset and waited for triggering. Here is the results.

Channel 0 at the top is Adressline, Channel 1 is AS and Channel 0 at the bottom is analogue adressline.

A1 to A13

: A1.png (89.03 KiB) Viewed 2793 times

: A2.png (76.87 KiB) Viewed 2793 times

: A3.png (81.5 KiB) Viewed 2793 times

: A4.png (66.11 KiB) Viewed 2793 times

: A5.png (80.63 KiB) Viewed 2793 times

: A6.png (71.04 KiB) Viewed 2793 times

: A7.png (74.47 KiB) Viewed 2793 times

: A8.png (72.26 KiB) Viewed 2793 times

: A9.png (61.76 KiB) Viewed 2793 times

: A10.png (69.96 KiB) Viewed 2793 times

: A11.png (65.88 KiB) Viewed 2793 times

: A12.png (80.23 KiB) Viewed 2793 times

: A13.png (85.45 KiB) Viewed 2793 times

Posted: **20 Aug 2021 19:57**

A14 - A23

: A14.png (67.24 KiB) Viewed 2793 times

: A15.png (64.32 KiB) Viewed 2793 times

: A16.png (62.18 KiB) Viewed 2793 times

: A17.png (63.74 KiB) Viewed 2793 times

: A18.png (75.5 KiB) Viewed 2793 times

: A19.png (75.65 KiB) Viewed 2793 times

: A20.png (82.09 KiB) Viewed 2793 times

: A21.png (59.57 KiB) Viewed 2793 times

: A22.png (86.5 KiB) Viewed 2793 times

: A23.png (86.08 KiB) Viewed 2793 times

Posted: **20 Aug 2021 20:15**

It seems to be stuck in a loop accessing address zero. If you have your scope on AS and ROM_CE...

CE is the bottom right pin of U2, and goes to pin 22 of the ROM on the highlighted track..

So first check you have continuity between those two points,And when you know which pin on the ROM IC it is, use your scope on that pin along with AS. You should see both pulse low at the same time after reset / power up.

: Capture.JPG (113.01 KiB) Viewed 2786 times

Posted: **20 Aug 2021 22:05**

I measured the pin on the rom and the bottom right pin on that chip and there was connection. Then i did a measure with the probe when i released reset.

Here is the results:

: romce.png (94.69 KiB) Viewed 2769 times

Posted: **20 Aug 2021 22:27**

Thanks. So the CPU is trying to access ROM, just it's not getting anywhere at all.

Have you checked there is activity on the databus after reset ? ( no need to post images of it all)

I also suggest you continuity check the address and databus from the CPU to the ROM IC. (note the ROM only goes up to A16) .

Also check for shorts on the CPU. Meter out pins next to each other all the way around the CPU and make sure no pins next to each other or shorting out.

GLUE must be working as it's decoding address zero and issuing DTACK etc When the ROM puts data on the bus the CPU should jump to a new address, but it's not doing that.

Just to be sure, you did not change anything on the board (like the ROM) at all before it suddenly stopped working ?

Also (without power on) check resistance from all the address and databus pins to 5V and make sure they are something like 2.2K or 4.7K etc.

Posted: **20 Aug 2021 23:24**

exxos wrote: 20 Aug 2021 22:27 Thanks. So the CPU is trying to access ROM, just its not getting anywhere at all.

Have you checked there is activity on the databus after reset ? ( no need to post images of it all)

I also suggest you continuity checked the address and databus from the CPU to the ROM IC. (note the ROM only goes up to A16) .

Also check for shorts on the CPU. Meter out pins next to each other all the way around the CPU and make sure no pins next to each other or shorting out.

GLUE must be working as its decoding address zero and issuing DTACK etc When the ROM puts data on the bus the CPU should jump to a new address, but its not doing that.

Just to be sure, you did not change anything on the board (like the ROM) at all before it suddenly stopped working ?

Also (without power on) check resistance from all the address and databus pins to 5V and make sure they are something like 2.2K or 4.7K etc.

I found that there was no connection between the ROM and CPU on address line 12, other lines had connection.

The resistance was good and varied between 1 - 2.2 but there was one pin (pin 20) that had a resistance of 5K ohm.

I did not remember doing much with the board while waiting for TF536 to arrive. Sadly though a pin broke loose yesterday on the chip that has 2.06 and 1.04 when i tried to straighten them. But i have two other roms with 2.06 and EmuTOS. I just don't know which bank they are in so i just test both banks on both roms.

/zChris

Posted: **20 Aug 2021 23:43**

Is this the pin that should be connected to A12 ?

: bugg.png (1.9 MiB) Viewed 2754 times

Posted: **20 Aug 2021 23:45**

I have tried to highlight A12 for you..

: 1.JPG (232.91 KiB) Viewed 2753 times

: 2.JPG (285.77 KiB) Viewed 2753 times

: 3.JPG (304.76 KiB) Viewed 2753 times

Posted: **20 Aug 2021 23:52**

This may be better https://www.exxosforum.co.uk/forum/view ... 778#p38968

Posted: **21 Aug 2021 11:42**

By the way, the left leg of C21 doesn't look very well soldered. Can see straight through the hole.

exxos's Atari, Amiga & retro forum

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