Signs of bad IC?

Hey all,

I'm in a microcomputer hw/sw class where we are building a
microprocessor board using an 8088.  I wire wrapped the clock circuit
and the reset circuit before testing it with the 8088 in its socket,
and all seemed to be fine (voltage tests, and frequency on the clock).
When I put the 8088 in its socket I was getting a short between VCC and
Ground on the power supply.  When I removed the 8088 the short
disappeared.  Is this a sign of a bad chip?  That is, getting short
between the VCC and Ground pins?  I rewired all of my VCC and Ground
pins with decoupling capacitors and the problem still exists, but only
with the chip in its socket.

Any help would be appreciated.
Thanks

carsonbj@gmail.com <carsonbj@gmail.com> wrote:
> Hey all,
> 
> I'm in a microcomputer hw/sw class where we are building a
> microprocessor board using an 8088.  I wire wrapped the clock circuit
> and the reset circuit before testing it with the 8088 in its socket,
> and all seemed to be fine (voltage tests, and frequency on the clock).
> When I put the 8088 in its socket I was getting a short between VCC and
> Ground on the power supply.  When I removed the 8088 the short
> disappeared.  Is this a sign of a bad chip?  That is, getting short
> between the VCC and Ground pins?  I rewired all of my VCC and Ground
> pins with decoupling capacitors and the problem still exists, but only
> with the chip in its socket.

It *might* be a bad chip, but it is also possible that you made a
mistake with the pin assignments - double check if you got all the pin
numbers right, and that you are using the datasheet of the proper IC
package.

-- 
:wq
^X^Cy^K^X^C^C^C^C

Yes, or misidentified (misconnected) pins on the IC.  If the latter, then 
you may have damaged the chip.

<carsonbj@gmail.com> wrote in message 
news:1159649212.908933.11270@m7g2000cwm.googlegroups.com...
> Hey all,
>
> I'm in a microcomputer hw/sw class where we are building a
> microprocessor board using an 8088.  I wire wrapped the clock circuit
> and the reset circuit before testing it with the 8088 in its socket,
> and all seemed to be fine (voltage tests, and frequency on the clock).
> When I put the 8088 in its socket I was getting a short between VCC and
> Ground on the power supply.  When I removed the 8088 the short
> disappeared.  Is this a sign of a bad chip?  That is, getting short
> between the VCC and Ground pins?  I rewired all of my VCC and Ground
> pins with decoupling capacitors and the problem still exists, but only
> with the chip in its socket.
>
> Any help would be appreciated.
> Thanks
> 

carsonbj@gmail.com wrote:
> Hey all,
>
> I'm in a microcomputer hw/sw class where we are building a
> microprocessor board using an 8088.  I wire wrapped the clock circuit
> and the reset circuit before testing it with the 8088 in its socket,
> and all seemed to be fine (voltage tests, and frequency on the clock).
> When I put the 8088 in its socket I was getting a short between VCC and
> Ground on the power supply.  When I removed the 8088 the short
> disappeared.  Is this a sign of a bad chip?  That is, getting short
> between the VCC and Ground pins?  I rewired all of my VCC and Ground
> pins with decoupling capacitors and the problem still exists, but only
> with the chip in its socket.
>
> Any help would be appreciated.
> Thanks

I did something similar to my 40 pin DIP Z80. I was careless and I
switched off my PSU to it and it sent a spike through the Z80 killing
it. Now everytime I hook it up I get a short fom Vcc to GND. Luckily I
had another (2 others) chip.

If it is doing it it is likely dead or you didn't wire the circuit
properly.

carsonbj@gmail.com wrote:
> Hey all,
>
> I'm in a microcomputer hw/sw class where we are building a
> microprocessor board using an 8088.  I wire wrapped the clock circuit
> and the reset circuit before testing it with the 8088 in its socket,
> and all seemed to be fine (voltage tests, and frequency on the clock).
> When I put the 8088 in its socket I was getting a short between VCC and
> Ground on the power supply.  When I removed the 8088 the short
> disappeared.  Is this a sign of a bad chip?  That is, getting short
> between the VCC and Ground pins?  I rewired all of my VCC and Ground
> pins with decoupling capacitors and the problem still exists, but only
> with the chip in its socket.
>
> Any help would be appreciated.
> Thanks

The short might not be real, maybe an artifact of the measuring device.
(I have seen it with 'big chips', CPU, FPGA...) So I would double check
the wiring and the pinout, and if everything is found OK, power the
board with a current limited power supply.
Of course you would be taking the risk of blowing the IC itself, not
that it matters if it is a bad IC.

A second note:  I seem to recall that the 8088 clock is generated with
an external crystal connected straight to the pins. If this is the
case, I don=B4t know how you did to check the clock frequency without
the CPU in its socket, but anyway, my advice is really only worth 2
cents.


Best regards

Josep Duran
If you are measuring the resistence oftesting the board