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I've been working on upgrading the memory in my Mega ST2 from 2MB to 4MB. 

 

I've desoldered the pads on the motherboard for the sockets, capacitors and resistors and have installed them.  I've checked continuity for all of the signals going to and from each socket (address lines, RAS, CAS, WE, Din/Dout, VDD and VSS) and everything looks good.  I'm just waiting on the 1MB DRAM chips to arrive at this point.

 

I ordered some NEC D421000C-60 chips from utsource, but they are taking forever, so I bought some Toshiba TC511001AP-70 chips on eBay.  I think they are right for this, but would appreciate some feedback on this if anyone knows.  Thanks!

 

Here's a pic of the installed components along with the Mean Well RD-50A PSU I have installed in this machine.  I'll post more after I get the machine working with the new memory.

a_sm.png

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Received the 1MB Toshiba chips today and got them installed this evening.

 

Worked the 1st time, booted right up to 4MB pf memory.  Ah, so satisfying.

 

 

st2_4mb_b_sm.png

st2_4mb_d_sm.png

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@Colleton I have considered doing this exact upgrade to my Mega ST2 but honestly have butterflies in the gut about doing it to a perfectly functional specimen...  Do you have a BOM for the sockets, caps and resistors?  Also, are these the RAM chips you used: eBay Listing

 

PS: I like your idea on the PSU replacement :) 

 

 

Mega ST2.jpg

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I have a MegaST2 that never had the holes put in for the 2nd bank.. so I cant do it that way even if I wanted to.  I could do Exxos upgrade.. but thats it..   But I will use this one as a games machine. 2mb is all you need for games.

 

James

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4 hours ago, swatcop said:

@Colleton I have considered doing this exact upgrade to my Mega ST2 but honestly have butterflies in the gut about doing it to a perfectly functional specimen...  Do you have a BOM for the sockets, caps and resistors?  Also, are these the RAM chips you used: eBay Listing

 

PS: I like your idea on the PSU replacement :) 

 

 

Mega ST2.jpg

Is that your machine in the picture swatcap? if so.. what files did you use for your USatan?   I have one I might install internal as well.. not a Lotharek so I need to change the slots (mine is microSd)   but otherwise support looks good.

 

James

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I just really need to know what resistors and capacitors to order.  Pretty confident the RAM chips I found are the same ones Colleton used.  

 

This may be the project that pushes me to order a desoldering gun finally.

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Posted (edited)
36 minutes ago, Bikerbob said:

Is that your machine in the picture swatcap? if so.. what files did you use for your USatan?   I have one I might install internal as well.. not a Lotharek so I need to change the slots (mine is microSd)   but otherwise support looks good.

 

James

@Bikerbob yes, that is my machine.  I designed the mount because I couldn't find anything out there already made.  In the pic you can see the remnants of failures during the design process of the .STL  😂

 

I have attached the .STL for you to tinker with.  Good luck!

MegaST_UltraSatan.stl

Mega US.jpg

Edited by swatcop
Edited to add picture
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3 minutes ago, swatcop said:

@Bikerbob yes, that is my machine.  I designed the mount because I couldn't find anything out there already made.  In the pic you can see the remnants of failures during the design process of the .STL  😂

 

I have attached the .STL for you to tinker with.  Good luck!

MegaST_UltraSatan.stl 32.89 kB · 1 download

Ha Tinker! I get it ;)

 

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5 hours ago, swatcop said:

@Colleton I have considered doing this exact upgrade to my Mega ST2 but honestly have butterflies in the gut about doing it to a perfectly functional specimen...  Do you have a BOM for the sockets, caps and resistors?  Also, are these the RAM chips you used: eBay Listing

 

PS: I like your idea on the PSU replacement :)

 

Yes, this was a scary job for me.  I thought about it for a few months before actually doing it.  The hardest part was desoldering the empty pads on the motherboard.  I have a fine tip Weller soldering iron and one of those blue plastic manual pump solder suckers.

 

After you have everything desoldered you need to ohm all of the traces I listed in the OP for continuity, to make sure you haven't lifted any.  Sadly, I lifted two traces.  Both were at the end of several hours spent desoldering and I guess I got sloppy.  I used some 24 gauge solid core wire for bodge wiring and was able to fix the two traces.

 

The BOM would be 16 18 pin sockets, 16 .1uf caps (I used ceramic disc caps) and 3 33 ohm resistors. tf_hh says you may need 68 ohm resistors instead of 33 ohm on some machines so I ordered those as well, but didn't need them.

 

Yes, those are the exact DRAM chips I used.

 

So, this is what I used:

 

1. A 20 piece set of 18 pin sockets from Juried Engineering on eBay.

2. Two 10 piece sets of .1uf ceramic disc caps from resistorsandmore on eBay.

3. One 10 piece set of 33 ohm resistors and another set of 68 ohm resistors, both from resistorsandmore.

4. Two sets of 8 pieces of the Toshiba DRAM you listed above.

 

The sockets were nothing special but worked well for me.  If I had been ordering the resistors from somewhere like DigiKey, I would have bought 1/4 watt resistors.  Since it was eBay, I bought what was available (1/2 watt).

 

Good luck!

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13 hours ago, Colleton said:

So, this is what I used:

1. A 20 piece set of 18 pin sockets from Juried Engineering on eBay.

2. Two 10 piece sets of .1uf ceramic disc caps from resistorsandmore on eBay.

3. One 10 piece set of 33 ohm resistors and another set of 68 ohm resistors, both from resistorsandmore.

4. Two sets of 8 pieces of the Toshiba DRAM you listed above.

@Colleton Thanks!  Thats exactly what I needed to know.  When trying to find the specifications for the caps and resistors through normal search means my Google-fu was weak sauce.  Either I didn't put in the specific terms or the info just hasn't been posted before?!?  Regardless, I'm ordering the parts and hopefully this helps others in the future.

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@snarkdluG Man I must have just missed your message (should subscribe I suppose) and ordered the 1/2 watt version...  Just ordered 33 and 68 ohm  1/4 watt resistors you linked.  Luckily it was the cheapest part.  Out of curiosity, and sorry for the dumb question, but what is the difference in application?  The 1/4 watt offer more protection to the circuit or?

 

Today was a pretty expensive day 🤑.  Bought a Hakko 301 desoldering gun too because the thought of desoldering 18 holes X 16 chip receptacles + resistor + capacitor holes had me cringing.  Also have to replace the NVRAM chip in my Falcon which I have been dreading, and a couple other odd jobs, so it'll be a lot of time and effort saved. 

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2 hours ago, swatcop said:

@snarkdluG Man I must have just missed your message (should subscribe I suppose) and ordered the 1/2 watt version...  Just ordered 33 and 68 ohm  1/4 watt resistors you linked.  Luckily it was the cheapest part.  Out of curiosity, and sorry for the dumb question, but what is the difference in application?  The 1/4 watt offer more protection to the circuit or?

 

Today was a pretty expensive day 🤑.  Bought a Hakko 301 desoldering gun too because the thought of desoldering 18 holes X 16 chip receptacles + resistor + capacitor holes had me cringing.  Also have to replace the NVRAM chip in my Falcon which I have been dreading, and a couple other odd jobs, so it'll be a lot of time and effort saved. 

 

In short, the watt rating tells you how much current you can run through the resistor before it overheats and burns up. 1/2 watt can handle more current. The old Atari board can fit either since the hole placement of the resistor is so far apart. 1/2W is a little bit bigger then 1/4W. All the stuff on the Atari is 5V. 

 

A desoldering gun is worth gold when doing this as a hobby. Everything becomes so much easier. 

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