Looking for obsolete DRAM chips

Hi,

I am restoring an old NorthStar Horizon which contains some dynamic
memory boards. During the testing I have found that several DRAM
chips are bad and require replacement. However, obtaining these parts
is difficult since they are long obsolete.

If anyone has any old DRAM chips they would like to part with, I will
gladly buy some from you, pay for shipping and all that. The specific
parts I am looking for are:

Mostek MK4108-30 (8Kx1)
Texas Instruments TMS4108-20 (8Kx1)
Texas Instruments TMS4027-20 (4Kx1)

Equivalent parts are OK but according to the NorthStar documentation,
the boards require specific DRAM chips and most substitutions can only
be made on an entire board basis. In other words, I would likely need
to replace all the DRAM chips to use another part depending on what it
is.

Thanks in advance for any help and/or advice regarding this.

Andrew Lynch

On Jul 14, 9:24 pm, lync...@yahoo.com wrote:[color=blue]
> Hi,
>
> I am restoring an old NorthStar Horizon which contains some dynamic
> memory boards. During the testing I have found that several DRAM
> chips are bad and require replacement. However, obtaining these parts
> is difficult since they are long obsolete.
>
> If anyone has any old DRAM chips they would like to part with, I will
> gladly buy some from you, pay for shipping and all that. The specific
> parts I am looking for are:
>
> Mostek MK4108-30 (8Kx1)
> Texas Instruments TMS4108-20 (8Kx1)
> Texas Instruments TMS4027-20 (4Kx1)
>
> Equivalent parts are OK but according to the NorthStar documentation,
> the boards require specific DRAM chips and most substitutions can only
> be made on an entire board basis. In other words, I would likely need
> to replace all the DRAM chips to use another part depending on what it
> is.
>
> Thanks in advance for any help and/or advice regarding this.
>
> Andrew Lynch[/color]

Hi,

Just a quick update to this posting. I have located some 4116 DRAM
chips at a local electronics surplus store and thought to try them as
a substitute for the 4108 parts. I checked online and the 4108 and
the 4116 share very similiar if not identical pinouts so it seemed
reasonable to me. It wastes 50% of the 4116 capacity but saves 100%
of the RAM board so it is worth it.

On both boards I tried substituting the 4116 for the broken 4108 DRAM
parity bit chips and it seems to work. I am no longer getting parity
error LED lighting like I was before and both boards seem to pass the
NorthStar Monitor 5.1 memory test command in the regions with the
substituted chips.

It looks like this is working. Does anyone know if there are any
problems with substituting the 4116 for the 4108 chips? Otherwise I
am moving these boards from the "broken but sort of working" into the
"working" pile.

I would still like to locate some 4108 DRAM chips. I heard from a
friend that [url]http://www.newcountryenterprises.com/[/url] has some 4108's but
now I am not sure it is worth getting them if the 4116's will work,
especially to get enough to above the minimum order level.

I found [url]http://unicornelectronics.com/[/url] carries the MK4027 DRAM chips.
I ordered some from them along with some other RAM chips for other
boards anticipating more bad chips.

Thanks!

Andrew Lynch

It's possible that a 4108 ***IS*** a 4116 with a defect (or multiple
defects all in the same half of the chip), and that the chip is simply
configured internally to only use the upper or lower half of the chip
(the half in which the defect is NOT located).

This strategy was fairly common in the 16K to 64K dram days, it allowed
the chip makers to use chips that would otherwise have been discarded,
and in so doing it cut the cost of memory.


[email]lynchaj@yahoo.com[/email] wrote:[color=blue]
> On Jul 14, 9:24 pm, lync...@yahoo.com wrote:[color=green]
>> Hi,
>>
>> I am restoring an old NorthStar Horizon which contains some dynamic
>> memory boards. During the testing I have found that several DRAM
>> chips are bad and require replacement. However, obtaining these parts
>> is difficult since they are long obsolete.
>>
>> If anyone has any old DRAM chips they would like to part with, I will
>> gladly buy some from you, pay for shipping and all that. The specific
>> parts I am looking for are:
>>
>> Mostek MK4108-30 (8Kx1)
>> Texas Instruments TMS4108-20 (8Kx1)
>> Texas Instruments TMS4027-20 (4Kx1)
>>
>> Equivalent parts are OK but according to the NorthStar documentation,
>> the boards require specific DRAM chips and most substitutions can only
>> be made on an entire board basis. In other words, I would likely need
>> to replace all the DRAM chips to use another part depending on what it
>> is.
>>
>> Thanks in advance for any help and/or advice regarding this.
>>
>> Andrew Lynch[/color]
>
> Hi,
>
> Just a quick update to this posting. I have located some 4116 DRAM
> chips at a local electronics surplus store and thought to try them as
> a substitute for the 4108 parts. I checked online and the 4108 and
> the 4116 share very similiar if not identical pinouts so it seemed
> reasonable to me. It wastes 50% of the 4116 capacity but saves 100%
> of the RAM board so it is worth it.
>
> On both boards I tried substituting the 4116 for the broken 4108 DRAM
> parity bit chips and it seems to work. I am no longer getting parity
> error LED lighting like I was before and both boards seem to pass the
> NorthStar Monitor 5.1 memory test command in the regions with the
> substituted chips.
>
> It looks like this is working. Does anyone know if there are any
> problems with substituting the 4116 for the 4108 chips? Otherwise I
> am moving these boards from the "broken but sort of working" into the
> "working" pile.
>
> I would still like to locate some 4108 DRAM chips. I heard from a
> friend that [url]http://www.newcountryenterprises.com/[/url] has some 4108's but
> now I am not sure it is worth getting them if the 4116's will work,
> especially to get enough to above the minimum order level.
>
> I found [url]http://unicornelectronics.com/[/url] carries the MK4027 DRAM chips.
> I ordered some from them along with some other RAM chips for other
> boards anticipating more bad chips.
>
> Thanks!
>
> Andrew Lynch
>[/color]

Hi,

See my posting on July 15 for details.

The short version: Yes, 4116s are good substitutes for any of the four
varieties of 4108.

Martin

[email]lynchaj@yahoo.com[/email] wrote:[color=blue]
>
> On Jul 14, 9:24 pm, lync...@yahoo.com wrote:[color=green]
> > Hi,
> >
> > I am restoring an old NorthStar Horizon which contains some dynamic
> > memory boards. During the testing I have found that several DRAM
> > chips are bad and require replacement. However, obtaining these parts
> > is difficult since they are long obsolete.
> >
> > If anyone has any old DRAM chips they would like to part with, I will
> > gladly buy some from you, pay for shipping and all that. The specific
> > parts I am looking for are:
> >
> > Mostek MK4108-30 (8Kx1)
> > Texas Instruments TMS4108-20 (8Kx1)
> > Texas Instruments TMS4027-20 (4Kx1)
> >
> > Equivalent parts are OK but according to the NorthStar documentation,
> > the boards require specific DRAM chips and most substitutions can only
> > be made on an entire board basis. In other words, I would likely need
> > to replace all the DRAM chips to use another part depending on what it
> > is.
> >
> > Thanks in advance for any help and/or advice regarding this.
> >
> > Andrew Lynch[/color]
>
> Hi,
>
> Just a quick update to this posting. I have located some 4116 DRAM
> chips at a local electronics surplus store and thought to try them as
> a substitute for the 4108 parts. I checked online and the 4108 and
> the 4116 share very similiar if not identical pinouts so it seemed
> reasonable to me. It wastes 50% of the 4116 capacity but saves 100%
> of the RAM board so it is worth it.
>
> On both boards I tried substituting the 4116 for the broken 4108 DRAM
> parity bit chips and it seems to work. I am no longer getting parity
> error LED lighting like I was before and both boards seem to pass the
> NorthStar Monitor 5.1 memory test command in the regions with the
> substituted chips.
>
> It looks like this is working. Does anyone know if there are any
> problems with substituting the 4116 for the 4108 chips? Otherwise I
> am moving these boards from the "broken but sort of working" into the
> "working" pile.
>
> I would still like to locate some 4108 DRAM chips. I heard from a
> friend that [url]http://www.newcountryenterprises.com/[/url] has some 4108's but
> now I am not sure it is worth getting them if the 4116's will work,
> especially to get enough to above the minimum order level.
>
> I found [url]http://unicornelectronics.com/[/url] carries the MK4027 DRAM chips.
> I ordered some from them along with some other RAM chips for other
> boards anticipating more bad chips.
>
> Thanks!
>
> Andrew Lynch[/color]
-------------------
Yes, the 4108 was a 4116 with one half of it having errors erred out
by fuse. I have a bunch of those, and I ALSO have a bunch of Intel
2118's which are the same chip as the 4116, but which uses ONLY +5V
and much lower power!!!

Want some?
-Steve
--
-Steve Walz [email]rstevew@armory.com[/email] [url]ftp://ftp.armory.com/pub/user/rstevew[/url]
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
[url]http://www.armory.com/~rstevew[/url] or [url]http://www.armory.com/~rstevew/Public[/url]

[email]lynchaj@yahoo.com[/email] wrote:[color=blue]
> Hi,
>
> I am restoring an old NorthStar Horizon which contains some dynamic
> memory boards. During the testing I have found that several DRAM
> chips are bad and require replacement. However, obtaining these parts
> is difficult since they are long obsolete.
>
> If anyone has any old DRAM chips they would like to part with, I will
> gladly buy some from you, pay for shipping and all that. The specific
> parts I am looking for are:
>
> Mostek MK4108-30 (8Kx1)
> Texas Instruments TMS4108-20 (8Kx1)
> Texas Instruments TMS4027-20 (4Kx1)
>
> Equivalent parts are OK but according to the NorthStar documentation,
> the boards require specific DRAM chips and most substitutions can only
> be made on an entire board basis. In other words, I would likely need
> to replace all the DRAM chips to use another part depending on what it
> is.
>
>
>[/color]
I have two Ram16 Boards
One has MK4115j-40's in Row 1 and the other three have 4027 3D's in
them Column 9 is empty but Cols 10-17 are filled
The Other has TMS4027-20NL's with Col 9 empty and cols 10-17 filled.
I am in the process of Replacing the Missing 7805 & 7812 's. Couple of
missing chips but will get them as well
I found that Unicorn Electronics has some MK-4027 250 ns and B.G. Micro
lists some 4027 4Kx1 250's as well
So Once I get that done mebbe I can get them Tested???
Bob in Wisconsin

"Robert J. Stevens" <ztrebora@execpc.com> wrote in message
news:46F3D37B.5040304@execpc.com...[color=blue]
> [email]lynchaj@yahoo.com[/email] wrote:[color=green]
>> Mostek MK4108-30 (8Kx1)
>> Texas Instruments TMS4108-20 (8Kx1)
>> Texas Instruments TMS4027-20 (4Kx1)
>>[/color]
> I found that Unicorn Electronics has some MK-4027 250 ns and B.G. Micro
> lists some 4027 4Kx1 250's as well[/color]

This place [url]http://www.residualstock.com/[/url] on their look-up function claims to
have all three of the parts you're looking for.

I've never done business with them, but a friend who restores pin-ball
machines has and says they're OK.

- Bill