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Richard Giroux

Faulty RAM on 800XL - what ram to buy

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I have an 800XL that fails the ram test. The chips on the board say "Mtu 4264-15 USA". Motherboard says REV-D.

 

The board is not socketed so I would like to by RAM and sockets. What RAM do I buy?

 

Exact replacement from China like this?

 

Can I buy a C64 kit like this

 

Or do I buy RAM like this and get my own sockets?

 

 

In other words, what are the specs for the replacement RAM chips?

Edited by Richard Giroux

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4164 chips (16pin) but various companies use various name variations!....

both your listed options look fine to me. i think there is a limit to no less than 100ns chip speed rating

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might as well do a ram upgrade at the same time, put more under the hood! It's the best time to do it!

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It was my understanding that I had to either fix or remove bad RAM chips for an upgrade. Is there an easy upgrade like piggybacking or chip drop-in replacement that doesn't need a secondary daughter-card? (Or bypass the onboard chips without introducing noise on the MB?)

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I have an 800XL that fails the ram test. The chips on the board say "Mtu 4264-15 USA". Motherboard says REV-D.

 

The board is not socketed so I would like to by RAM and sockets. What RAM do I buy?

 

Exact replacement from China like this?

 

Can I buy a C64 kit like this

 

Or do I buy RAM like this and get my own sockets?

 

 

In other words, what are the specs for the replacement RAM chips?

What is the part number of your ANTIC chip (C012296 or C021697)? The C012296 has a 7 bit refresh counter and works with 64Kx1 DRAM with 128 cycle refresh. The C021697 has an eight bit refresh counter and works with 256 cycle 64Kx1 DRAM with 256 cycle refresh.

 

Memory kit 8 x KM4164B - 12 & sockets DRAM 4164 Apple IIe Commodore 64 128 Oric (This kit is 64Kx1, but a 128 cycle refresh or 2ms)

 

10pcs MT4264-15 MT 4264-15 IC Chip DIP16 (This set is 64x1, and had 256 cycle refresh or 4ms)

 

10pcs MN4164P-15A NMOS 65,536 X 1 BIT DYNAMIC RAM DIP (This set is 64Kx1, but a 128 cycle refresh or 2ms)

 

I'd personally stay away from the MT4264 (Micron) and buy a different manufacturer. They have a bad reputation for 64K DRAM. I think the C021697 will work with both 128 and 256 cycle refreshed DRAM (it just refreshes twice).

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Thanks for the detailed reply.

 

The Antic chip is a C021697-01 so if I am reading this right, I can use any of the suggestions I posted but it is best if I stick with the 256 cycle chips.

Edited by Richard Giroux

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@Richard:

 

The important things about the right RAM chips are already told.

 

But... How is your experience with Atari 8-Bit? If you´re doing the first technical steps with such an old system, it´s better to do it step-by-step. First fix the defects, then think about expansions. There are a lot of new developments, some useful, some not. You will find a lot of infos here at AtariAge :)

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Thanks for the advice...keep it coming. This is my first Atari in 30+ years and I am not particularly good at the electronics. I've had limited success at de-soldering so here is the plan:

 

 

@everyone

 

1. Practice de-soldering on a junk PC board...

2. Test the existing RAM chips using the piggy-back method.

3. Clip the old chip off leaving the legs behind.

4. De-solder and remove the legs.

5. Install a socket.

6. Install a new RAM chip (4164).

7. Pray

8. Test

9. Repeat 3-8

10. Plan the memory upgrade - submit photos to the forum for error checking and comments (and documentation for others)

11. Install memory upgrade.

12. Post photos of finished result.

 

 

 

 

 

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What about a soldering iron? What do you guys recommend?

I use a cheap 30 watt Radio Shack solder iron I bought in the 90's. I use a simple pump once type vacuum solder sucker. You need to be careful not to put too much heat on a given spot. Don't let the iron sit there for 10 seconds especially if its a 30 watt iron. You can de-bond the traces and/or through holes from the PCB if you get it too hot for too long. I like your idea of cutting the legs first. That way you can grab the leg leads with a tiny pair or tweezers and pull the leg out while you heat it. That should minimize the time you have to hold the iron on the board, but you still have to suck out the through holes to make room for the new socket.

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@Richard:

 

The important things about the right RAM chips are already told.

 

But... How is your experience with Atari 8-Bit? If you´re doing the first technical steps with such an old system, it´s better to do it step-by-step. First fix the defects, then think about expansions. There are a lot of new developments, some useful, some not. You will find a lot of infos here at AtariAge :)

True, but there is no point in purchasing replacement 4164 chips if considering a 256k upgrade. The 41256 chips are backward compatible with standard 4164s if pin 1 is grounded, and are often the same price or less.

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Hello guys,

 

today I got 800XL board from auction (sold as is and only board without any other hardware)...

When tried to run it goes immediately into self test and except ROm passing it fails on most of RAM...

Antic is C021-698-01 and board is Rev-D.

Can you recommend me the correct memory to buy please?

I would like to saty away from Micron...

 

As it goes directly to self-test (nothing pressed on keyboard while turning ON) does it seems that also other chips are failing?

 

many thanks for help,

 

Petr

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probably just the RAM if it is going in to self test 
These would be ok
https://www.ebay.co.uk/itm/4164-RAM-64Kx1Bit-150ns-100-tested-UK-SELLER-same-day-despatch/333715067932?hash=item4db2f7d41c:g:dB8AAOSwellfLz19

 




or there are options to bypass the original RAM such as https://lotharek.pl/productdetail.php?id=291
If it were me though, I would buy a syscheck from tf_hh as this will also help you to diagnose some issues , give you alternative OS's and RAM upgrade



 

Edited by mimo

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Many thanks for great help.

I ordered them from that link you posted :) already so I hope that they will work in my 800XL together with ATIC C021698-01...:)

 

Petr

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Hi folks,

 

just FYI...

RAM piggyback trick did not helped. No change in MEM self-test results when I swapped the chips in sockets positions...

New ICs ordered so we will see.

 

rgds,

Petr

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Hi all,

 

as my first mother board of 800XL is waiting for RAM replacement (on its way to me) I tried to run the second one.

After few days of proper working it is failing too ...but strange graphics issue.

I never seen it before...

 

 

Petr

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On 10/13/2020 at 10:18 AM, ok1rp said:

as my first mother board of 800XL is waiting for RAM replacement (on its way to me) I tried to run the second one.

After few days of proper working it is failing too ...but strange graphics issue.

I never seen it before...

When you get the new RAM, you can try it in both systems to confirm it is only bad RAM first. Then you can continue from there, swapping chips one at a time from the "bad" machine into the "good" machine to identify remaining bad IC's.

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On 10/13/2020 at 5:18 PM, ok1rp said:

After few days of proper working

since it worked properly for a while, i would consider the power supply or GTIA/ANTIC issues.

check the output voltage is not too high or too low - try another PSU if you have one.

Any socketed chips ought to be removed and all contacts cleaned with contact cleaner

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Those 80s era mT ram chips don't age very well do they. 

 

Piggy back doesn't work most of the time. If the soldered IC is shorted and getting hot, you risk frying the RAM on top instantly.

 

It only works when the ICs gate is open which isn't common, not stuck permanently in any position [  hi, low or floating ] which is usually the case

 

If there is any failure mode that causes the bad chip to drive 0 or 5v, the good chip on top drives the opposite value which is the correct one.. . the two chips end up fighting each other where you have one driving 0v and the other driving 5v... not good.

 

 

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