Mega ST and TOS 2.06 decoder board

Upgrade or replace the ROM.
coonsgm
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Mega ST and TOS 2.06 decoder board

Post by coonsgm »

In preparation for installing this I’ve read through many posts in the forums here including the previous post by gwinter on the same topic and was hoping for any help if I’m missing something obvious.

I’ve performed the following mandatory fixes
- Installed a new Meanwell RD-50a PSU
- Added 10k pullup network to the DMA databus
- Swapped the 4.7k and 10k bus resistor arrays with 2.2k

The Mega performs great both before and after the upgrades with the 68k in the base socket and using the dual TOS board set to 1.04.
-I’ve checked the soldering and continuity on the socket added (multiple times)
-I’ve checked for continuity between the CPU socket and the D0-15 and A1-A16 ROM sockets…all good there.
-I’ve tried with the 16mhz jumper pads open and closed – see photo of installation
IMG_0999.jpeg
IMG_0999.jpeg (491.21 KiB) Viewed 4207 times
The issue I run into is the computer with either the 68k or a TF536 installed in the decoder board throws 11 bombs once it finishes the RAM check in TOS 2.06 and immediately throws bombs under 1.04. I did get it to the 2.06 desktop with the 68k installed and no flash drive in the gotek, but it immediately crashed once I inserted a flash drive and tried to access it.
IMG_0995.JPEG
IMG_0995.JPEG (234.74 KiB) Viewed 4207 times
I greatly appreciate any help!
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exxos
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Re: Mega ST and TOS 2.06 decoder board

Post by exxos »

Did it have a blitter patch on the CPU originally ?

Also wipe all pins with IPA in case its just simply a bad connection somewhere.. If you can't run a 68k in the decoder socket, then you may have a bad solder joint on the socket.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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coonsgm
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Re: Mega ST and TOS 2.06 decoder board

Post by coonsgm »

Yes, it did have a blitter patch but I removed it and added a bodge wire on the bottom to make the connection that was lost.
coonsgm
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Re: Mega ST and TOS 2.06 decoder board

Post by coonsgm »

I'll do the IPA wipe. I did check the socket continuity and I get it on all the pins soldered. Just rechecked.

There are two pins 11 and 15 where there is no continuity from the base that do not have continuity to the socket, but they didn't have continuity to the holes before I soldered in the socket. I assume that something is done with the input from them by the decoder board.
coonsgm
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Re: Mega ST and TOS 2.06 decoder board

Post by coonsgm »

Quick question, if I'm not running an accelerator do I still need the 16mhz line connected?
coonsgm
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Re: Mega ST and TOS 2.06 decoder board

Post by coonsgm »

Wiped down all pins on the decoder board, all both sockets, the dual TOS board, and the CPU pins twice just for good measure.

No joy with the IPA wipe.

Did the complete continuity re-check from bottom to top with the CPU and decoder board. Besides pins 11 and 15 I get continuity from the bottom of the board where the base socket is soldered in to the CPU pins on top....yes it was a bit of a yoga exercise to measure them.

If pins 11 and 15 should have continuity from the bottom of the board to the CPU pins, then the issue is in the decoder board (I don't think it is because the board has to have some inputs that it tweaks and doesn't just pass through).

The only thing I can think of is it is somehow having issues with communication with the drives in some way as I can consistently get to the 2.06 desktop so long as no floppy is in the drive, no flash drive is in the floppy and no Ultrasatan is plugged in. Once I try to access the floppy or gotek, I get bombs.
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exxos
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Re: Mega ST and TOS 2.06 decoder board

Post by exxos »

coonsgm wrote: Tue Mar 02, 2021 1:33 am Quick question, if I'm not running an accelerator do I still need the 16mhz line connected?
I assume that would be OK. You should be in 8mhz mode on the jumper also.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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exxos
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Re: Mega ST and TOS 2.06 decoder board

Post by exxos »

coonsgm wrote: Tue Mar 02, 2021 2:48 am If pins 11 and 15 should have continuity from the bottom of the board to the CPU pins, then the issue is in the decoder board (I don't think it is because the board has to have some inputs that it tweaks and doesn't just pass through).
Its not totally pass through... Pin 15 is CPU clock which has to be driven via the pld for 16mhz...
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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People should find solutions to problems, not find problems with solutions.
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exxos
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Re: Mega ST and TOS 2.06 decoder board

Post by exxos »

Are the GLUE and MMU also IMP chips ? That could be your problem. Isn't the IMP DMA supposed to have a diode in series with its power ?

MEGAs are the worst machine to upgrade and mix in IMP chips is asking for trouble... https://www.exxosforum.co.uk/atari/last/MEGAST/index.htm
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
dragmar
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Re: Mega ST and TOS 2.06 decoder board

Post by dragmar »

like @exxos says IMP chips are just problems. I tested the TOS2.06 board in a Mega rev 2.2 with IMP chips and it failed.
First, if you removed the patch blitter, 80% won't run mega.
Also, as @exxos IMP DMA mentioned, it is supposed to have a diode connected in series with its power.

I solved the problem in such a way that I got rid of all IMP chips, turned off the blitter and so I was able to move TOS206 and TF536 on rev 2.2
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