Dead TT030 Repair

[grunwald]

I received the 74HCT04 today and swapped it out. Magically, the unit now boots up into the Diagnostic cartridge and to the desktop. I ran all of the tests and everything but MCU set error came back good. I then added TT ram which also showed fine. An issue developed when I tried to add a 2 meg ST Ram board. With the cartridge in, I get continuous flashing blue/red screen with "Hello World". I checked the RS232 port and it is showing "I5 Ram sizing error" Without the cart, the system boots normally except, it does not recognize the additional 2mb. I tried two different memory boards, same result. I have not found much when searching for "Ram sizing error" Anyone seen this before?

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[DoG]

Does your 2Mb ST-ram card have a jumper on it?

[mikro]

My guess would be your ST RAM connector (assuming that the card works as it should in another machine). TT Field Service Manual says "Uppermost address fails" and Falcon's diagnostic cartridge source code says "not seeing second bank or top location is bad" (unfortunately the code using it had been removed for Falcon so we can't know what exactly it tested).

[stephen_usher]

Good news that you seem to be almost there.

I take it that you've done a visual inspection of the ST RAM sockets for bad connectors? Maybe pour some contact cleaner down them in case of tarnish and reseat the board a couple of times.

[grunwald]

All of the jumpers are in the same configuration on all on my 2mb boards. The boards work in my other TT030s. I went through the MB sockets and reflowed a couple that looked a little wonky, but no change. I have already changed all of the onboard RAM and it passes all tests.

[grunwald]

Had to go out of town for work so today was the first chance I've had to continue troubleshooting the board. I went through and checked all data, address, and MData lines to the memory connectors and all checked out OK. I went through the control lines as well and all seem to be active at some point in the boot cycle. The fact that it hangs with a I5 error when the diagnostic cartridge is in, but will boot to the desktop without it, is a bit strange, although it still does not recognize the additional 2mg of memory. I hooked up a bluescsi and a floppy drive, and both work with no issues. TT ram seems to be a bit unstable when running certain programs. I'm open to any and all ideas. I have gone back and checked all of my prior work and did not find any issues. I also swapped the ROMs just to eliminate them as a possibility.

[grunwald]

I went back and toned out every signal line on the ST memory card connector. Most go to the MMU which I have already replaced. All were good.I read that the onboard memory is shifted up top and replaced in low memory by the 2mb board when it is installed. Anyone know how this is facilitated and what hardware is impacted?

[grunwald]

Went back last night and focused on SEL and BNK5 signals. The following chart shows how memory is mapped dependent on whether the 2/8mb board is installed. The jumper on the board determines the state of BNK5.

Memory Register.jpg

When attempting to boot into the cartridge with the board in and jumpers set, BNK5 cycles high and low producing the I5 error as shown prior. Taking the jumper off allows the system to boot into the diagnostic menu. I currently have a total of four 2mb boards. three are good and one has some bad dram. What I found interesting is when running the ram test with the board installed (w/o jumpers). the test finds the bad dram on the bad board. I'm not sure if the board is replacing the onboard memory when plugged in w/o jumpers given that the system still only shows 2mb. The following pictures show two test runs, one with a good board, and one with the bad one.

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This tells me that all of the bus lines are working and that the system can read the board memory. Something is sending the system into a boot loop when accessing the board with the cartridge in.

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[grunwald]

Been out of town for a bit and just getting back on this project. I verified that the BNK5 and SEL lines on both of the MMUs (Mother board and Ram board), were properly pulled up or down accordingly. Jumping 1/2 on the RAM board's W1 Jumper connects BKN5 to SEL and pulls it high. This is what triggers the I5 error when booting into the Diagnostic cartridge. Without the cartridge, the system will boot normally, but will not recognize the extra 2Mb of Ram. Does anyone know how Configuration Register at FF8000 interacts with the BNK5/SEL lines to shift memory banks? Also, does anyone know what the Diag. Cart is checking for immediately after it displays "Hello World"? That may provide a clue what is stopping the system from recognizing the 2Mb board. The one other issue I found was when booted to the desktop, hitting Ctrl/Alt/Del does nothing. Not sure if this is connected. Other than these issues, everything else on the system seems to be working properly. This fault seems to be somewhat unique given that I have not found a single reference to the "I5 Error" on any of the Atari boards.

[exxos]

i5.PNG