[sdiy] Help ID a diode

[Phillip Gallo]

Schottky diodes would erode the voltage margin.  The two diode drops are
intended to ensure the gate negates chip select before the RAM's voltage
has dropped enough to allow spurious writes op's (or any ops) if /CS was
true.

p

On Sat, May 7, 2016 at 7:44 PM, MTG <grant at musictechnologiesgroup.com>
wrote:

> 0.6v approx.
>
>
> On 5/7/2016 7:27 PM, Barry Klein wrote:
>
>> Measure the Vdrop across each.
>>
>> Sent from my iPhone
>>
>> On May 7, 2016, at 6:12 PM, MTG <grant at musictechnologiesgroup.com> wrote:
>>>
>>> I have 2 diodes in a logic circuit that I am trying to ID. Their purpose
>>> (my best guess) I will explain below. They are in series so I assume they
>>> are the same.  They are both the orange glass type and look like a 1N4148
>>> or a 1N914, but the numbering is off.
>>>
>>> The first one has a stylized "F" and the numbers "25".
>>>
>>> The second has what looks like "T1" or maybe "TI" and then "525" as far
>>> as I can tell.
>>>
>>> The circuit is a 4011 logic circuit, part of the battery backup logic.
>>> The 4011 is powered by a diode combination of 5v or the 3v coin cell,
>>> whichever is larger.  Other diodes, not these ones.
>>>
>>> My attempt at deciphering...These diodes and 1/4 of the gate package are
>>> intended to disable a CE* signal when 5v goes away. I will attempt ascii
>>> draw:
>>>
>>>
>>>                                  |-----\
>>> "5v"----|>|---|>|----+-----------|      \
>>>                      |           | NAND  >0----RAM_CE*
>>>                      <    CE ----|      /
>>>                  10k <           |--- -/
>>>                      <
>>>                      |
>>>                     Gnd
>>>
>>> This is some home-brewed memory expansion (not mine) and it has issues
>>> where some of the bytes change after a while (possibly during
>>> power-cycling).  I don't know that this is the culprit but it's pretty odd
>>> by what I have seen around synths. I swapped out the RAM and it still
>>> occurs.
>>>
>>> Do you suppose these are schottky??  The number 25 or 525 means nothing
>>> to me in diode land.
>>>
>>> I may have to come up with some other solution, but I wanted to try
>>> swapping these out first.
>>>
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>>>
>>
>>
>>
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