28pin to 32pin EPROM conversion

Upgrade or replace the ROM.
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28pin to 32pin EPROM conversion

Post by exxos » Fri Feb 02, 2018 2:12 pm

Information taken from the archives on my website http://www.exxoshost.co.uk/atari/last/tos/index.htm to expect bad pictures :twisted:


"SOCKET METHOD"

I am going to upgrade the TOS to RAINBOW TOS 104. I upgrade the TOS using regular EPROM which have been programmed with the TOS 104 images already.

It is noted that the EPROM's are 1MBit and are slightly longer than the TOS ROMS's. The original TOS ROM's were OTP (one time programmable) and have less pins than EPROM's. Some wiring is needed to adapt them for ST use.

I use regular turn pin sockets for this upgrade. I find it makes things nice and neat. However, if you decide to use the sockets rather than doing all the wiring directly to the EPROM, then the ST metal shield will not seat correctly as the addition of the socket makes them too high to fit. So a small hole would have to be cut in the metal shield. There are many options though this socket example is the one which I shall go with in this series.

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First we must bend up and outwards the pin on the left of the IC. looking from the bottom, we count 8 pins up from the bottom left upwards. Notice the "tab" of both the socket and the IC are at the top of the image. If you get this part wrong you will wire your EPROM upside down!

Trim the bend lag back if needed. Also when you solder the bottom right pin try to only solder to the upper part of the pin and not allow the solder to run down the leg else it will not fit into the socket!

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Above we now have a top view of the finished wire.

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And the side view of the bent pin

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and the side view of the other connection. Notice the solder is only at the top of the leg as mentioned earlier!

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Now to start on the socket!

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Notice the IC tab is to the left of the image. We need to cut off level the 2 end pins. Do not cut them off totally as we need to solder some wires to them. This overhang the sockets on the motherboard and if not cut , could short out onto the PCB.

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Top 3 pins on the left are soldered together and linked to the top right pin only.

Then counting 8 pins up from the bottom left we link to the second pin down from the top right.

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Done! Slot the EPROM's into the sockets and that's it!

The EPROM on the left I took the wire directly over the EPROM as the black wire on the right is a little harder to see.

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Side view of the 2 finished EPROM's

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Now they are slotted into the motherboard. Notice the overhang the IC sockets by 2 pins!

As mentioned before, the EPROM on the bottom of the picture is physically higher than the ST's metal shield so some slight metal editing is needed, or you could always removed the socket on the motherboard and solder out new sockets in place. Or just do all the wiring directly to the EPROM though I find overall the outlined method to be the neatest way, other than some small metal editing!
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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Re: 28pin to 32pin EPROM conversion

Post by exxos » Fri Feb 02, 2018 2:14 pm

"LAZY ASS METHOD"

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For those who want to solder the EPROM directly it follows much the same as the socket method. however where the plane bare wire and black wire meet, they much not touch, this can be tricky in pushing the wire into the IC socket on the motherboard.

top 3 pins get soldered as before to the top right pin. Then the second pin down from the top on the right has a loose connection the other end where the EPROM pin was bent up.

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Notice the black wire (EPROM BENT PIN UP) is not touching the bare wire.

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We now have a nice RAINBOW TOS 104 installed and working :-)

I like rainbow tos as the FUJI is all different colours like a rainbow! and its even animated too!
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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Re: 28pin to 32pin EPROM conversion

Post by exxos » Fri Feb 02, 2018 2:16 pm

BETTER SOLUTIONS

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viewtopic.php?f=16&t=272
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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