[Coco] OT: electronics question

[David Gacke]

Hi James,

I know this may seem like a silly question, and no insult intended, but
are you counting the pins correctly?

They should be counted counter-clockwise when looking at the top of the
chip. Pin 1 should have a dot printed, or a dimple in the chip case just
above it. Also other common pin 1 markings are a notch in the side of
the chip where pin 1 is.

The problem could also be the torch.  :)

In either case, you can get 7400 series logic chips dirt cheap.
BGMicro.com is a nice place to buy onesies or them. I looked up the
price, it's 22 cents for a LS version of that '02.  I'm not sure about
you, but unless you're in REALLY dire need, I might be tempted just to
order another one.

Anyway, if you really want to remove them, and have a fairly heft
soldering iron, actually apply more solder to the bottom of the part.
It'll give you better heat transfer. This may allow it to melt all the
way thru so that it can be removed with a solder sucker.

If you can't get all the solder out, reapply some and then with a dental
pick, or really small screwdriver, start prying gently under it till you
can get it to start to tip. You'll need to heat several pins at a time
to get it to start to loosen and flex.

Good luck with it!


Dave

-----Original Message-----
From: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com]
On Behalf Of James Dessart
Sent: Tuesday, May 25, 2004 8:43 PM
To: CoCoList for Color Computer Enthusiasts
Subject: [Coco] OT: electronics question

I've got a 7402 I pulled from a board. I hooked it up to a 5v source 
and ground. When I sample the inputs, I get a lowish voltage (around 2 
volts, unconnected pins), but when I sample the output, regardless of 
how I drive the inputs, I get a really, really low voltage. Do I need 
to do something in particular to drive the inputs? I'm simply using a 
switch to vcc right now. Should I set it up with the switches 
triggering transistors?

It could be burned out, I used a butane torch to take it off the board. 
It's pretty thick PCB, and I can't seem to get the chips off any other 
way.

James


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