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

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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.

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

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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.

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Isaac Bosompem

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

Reply to
Josep Duran

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