Path: utzoo!attcan!utgpu!watmath!att!mcdchg!ddsw1!ddsw1!karl
From: karl@ddsw1.MCS.COM (Karl Denninger)
Newsgroups: comp.sys.ibm.pc
Subject: Interupt conflicts
Keywords: PC Bus
Message-ID: <[24ea313d:5029.1]comp.ibmpc;1@ddsw1.MCS.COM>
Date: 17 Aug 89 04:00:05 GMT
References: <1875@uceng.UC.EDU>
Lines: 48

>Item 5029 (0 resps) by kthompso at uceng.UC.EDU on Wed 16 Aug 89 09:29
>[ken thompson]    Subject: Interupt conflicts
>
>A friend of mine returned his AT clone back to the store for warrenty repair.
>The owner told him that he would have to buy a new mother board.  He said the 

>mother board had smoked because two boards were set on IRQ 4.  He said it also

>destroyed the hard drive.  He now refuses to fix or return the PC to him,
>says he may need it for evidence.
>
>I have installed boards with conflicting interrupts before and other than 
>software problems, there was no damage.  The interrupt chip is just a
>TTL input and shouldn't care how many highs are put on it's input.  I think
>my friend is getting the screws.
>
>Comments please!

Comments?  Here's some....

First, you CAN damage things by conflicting IRQ settings..... but --

You're most likely to damage the peripheral boards themselves.  You see, if
one board is driving the pin high, and the other driving it low, well, you
get to see how good a fuse some TTL level driver makes... on the peripheral
card itself.  In this case, you might fry a modem or serial board -- both of
which are on IRQ 4.

Since the motherboard doesn't drive _anything_ in this situation, it would
be slightly difficult to damage it with this type of mistake.  As for the
disk drive, that would be even harder, as it has no direct connection to the
main board at all; it's driven through a number of buffers and other
circuitry (the controller card of course).

I think your friend is getting the snow job.  I'd tell Mr. Clone Shop Owner
that you want the machine back, fixed, right now, or you are going to sue.
It sounds to me like someone is trying to make a lot of money for doing
nothing at all -- this clone shop person could simply fix the jumper settings,
charge your friend for a motherboard, and send him on his way -- lots poorer.

If you're willing to fly me to wherever the trial is, I'd even be willing to
testify in this one.  I run the shop here, and have lots and lots of
experience -- I bet I qualify as an expert witness :-)

==
Karl Denninger (karl@ddsw1.MCS.COM, !ddsw1!karl)
Public Access Data Line: [+1 312 566-8911], Voice: [+1 312 566-8910]
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