Re: cbm 8032 motherboard + 4164

----- Original Message ----- 
From: "Francesco Messineo" <francesco.messineo@gmail.com>
To: <cbm-hackers@musoftware.de>
Sent: Friday, October 07, 2016 1:41 PM
Subject: Re: cbm 8032 motherboard + 4164


> On Fri, Oct 7, 2016 at 6:45 PM, Mike Stein <mhs.stein@gmail.com> wrote:
>> I guess technically 'reversible' means being able to put things back *exactly* the way they were, especially without any soldering, so cutting and restoring traces, adding and removing sockets etc. would not qualify as 'reversible'.
>>
>> I've often wondered why it's standard practice to install a socket when replacing a single bad chip; presumably the odds of the same chip failing again are slim, and it certainly is a glaring 'modification'.
> 
> as I do quite a few repairs of old gears, I think I can give a number
> of reasons why I almost always install a socket:
> 1) most of the times, the failing chip is not alone, the replacement
> can be killed instantly by another fault: random example is a bus
> conflict where a failed input or output sinks/source
> current against another output, this in many cases makes the
> replacement fail soon again.
> 2) in the troubleshooting process, might often be good to
> isolate/replace a signal around a failed chip (because there're other
> related faults not yet identified), a socket makes this process
> easier.
> 3) it's cheap enough that even if you are sure there's no reason to
> fall in the 1) and 2) cases, you don't just take the chance to be
> wrong.
> 
> (all IMHO)
> 
> Frank
> 
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=========================
All valid reasons, although in my experience it often is only one chip and when it isn't it's often obvious what else is wrong.

But it's not about how much it costs, but whether you're concerned with keeping the board/system as close (or easily restorable) to original condition as possible, with some people even making sure that date codes on replacement chips match the rest of the system.

Different priorities for different folks...

m

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