RE: Repairing a SFD-1001 (8250/LP, 8050, 4040, 3040, 2040)

From: Hoffmann-Vetter, Martin <>
Date: Sun, 14 Aug 2011 12:07:46 +0200
Message-ID: <001001cc5a6a$051817c0$1b09a8c0@mhvnb10>
Hello Jim,

> The issue with that is the D0-D7 can't be left unconnected, so they
> need to be pulled to Vcc with jumpers to ground.

That's right.

> That's 8 resistors
> + 3 for the CS line pins + 3 for the additional address lines (3 + 3
> + 8 = 14).

No, you need only the 8 reststors and jumpers for D0-D7. The CS where direct
connected to A, B and C. No restistor is needed! If you have a "dont't care"
CS, you put an additional jumper at D0-D7.

E.g: CS1 it low aktiv, CS2 is don't care and C3 is high aktiv
 1  0/1  0 => Jumper 4 and 6

> The '138 approach requires only the resistors for the 3
> incoming CS lines and the 3 additional address lines (A13,14,15 - the
> design allows use of EPROMS/FLASH up to 27C512)  I can still do
> through hole with 6 resistors, but not with 14.

Okay, with the 151 you need 11 restistors. So you can jumper any combination
of the CS!

>> The other way is to use a comparator eg. 688.

> I think you meant '85.

No, the 85 hasn't an inverted output signal. You need an additional

> '688 is an 8 bit comparator, no need for that much...

That's true, but i think not the problem. It's a standard typ. Unused pins
can be grounded.


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Received on 2011-08-14 11:00:09

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