[sdiy] on the search for some MXR Digital Delay memory chips

[ChristianH]

I had a look at that big fat Intel data book from 1977 over the weekend.

Too bad, the 2107 was about the last dynamic RAM chip to use parallel
address lines, all later ones (including the 4164) have them multiplexed,
in order to reduce the number of pins. Even I would consider that a
challenge...

BUT - the chip pin interface doesn't look that much different to a
static RAM. The only significant difference ist that the 2107 has
separate data in and out lines. Depends on the circuit if that's really
needed, or if they are connected on the board anyway.

Christian



On Fri, 19 Sep 2008 16:39:31 +0200 ChristianH <chris at chrismusic.de>
wrote:

> On Fri, 19 Sep 2008 09:21:36 -0400 Todd Sines <sines_tr at scale.gs> wrote:
> 
> > I have 2 dead MXR blue face Digital Delay units that look like this:
> > http://www.sonicflux.com/pics/mxr_ptx_dd1_c2.jpg
> > [the one on the bottom]
> > 
> > Takeshi, the tech that has been repairing them, cannot find the  
> > memory ICs.
> > he gave me this list of possible ICs that might work.
> > 
> > "This is Memory IC of MXR.
> > long time ago. 4 or 5 company made this memory IC.
> > AM9060.
> > D2107C
> > uPD411
> > MM5280
> > TMS4060.
> > Sorry I do not know name of company.
> > so you can use any those type IC for MXR Digital Delay.
> 
> Gee, haven't seen those numbers in a long time...
> Looks like AMD (?), Intel, NEC, National (?) and Texas Instruments, in
> that order.
> 
> Was a faily standard dynamic RAM chip in the late 70s. I should have
> data sheets from Intel and NEC at home. IIRC, it's 4kBit. Wow, that's
> 4096 whole bits in one chip... <gr>
> 
> Maybe it's sufficiently similar to later dynamic RAMs, like the 4164,
> which I have seen quite recently at my supplier. Quite often later chips
> just have additional address inputs, due to the increased capacity.
> Might work to simply ground those inputs, and use only the needed part
> of the larger capacity.
> 
> > I imagine I'll need somewhere between 30-80 of these things. I got a  
> > ridiculous quote  for $580 for 100.
> > 
> > Anyone have a batch of the chips above that won't be more than $200  
> > total?
> 
> Unless there has been a misbehaving power supply unit, I wouldn't expect
> *lots* of memory chips dead.
> 
> If really all of the memory is shot it might be a worth considering 
> to redesign the circuit using current static RAM chips (may even be
> possible to replace the whole bunch with a single chip). If you have a
> schematic, that is. 
> Most certainly not for the faint of heart, but this is diy ;-)
> 
> Christian