Re: Multilayer board, track tracing?


"JB" <nospam@xxxxxxxxxxxx> wrote in message
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"Arfa Daily" <arfa.daily@xxxxxxxxxxxx> wrote in message
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"David Nebenzahl" <nobody@xxxxxxxxxxxxxxx> wrote in message
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On 5/19/2009 7:42 AM Gareth Magennis spake thus:

"Arfa Daily" <arfa.daily@xxxxxxxxxxxx> wrote in message
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"N_Cook" <diverse@xxxxxxxxx> wrote in message
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Any tips for single ended signal injection and tracing for high
resolution tracing , floppy/HD head as searchcoil ?

I would have thought that any tracks which passed internally between
power and ground planes, would have struggled to radiate
enough signal to be picked up in the way that you are envisioning.
Also, where there are fine-pitch 'bunches' of tracks which run
parallel to one another for any distance, I would think that
crosstalk might become a problem to this technique. If such a board
has any (internal) tracking problems, I don't think that you are
going to do a lot with it anyway. Even if it is just generally
faulty in some way, if the board is complex enough to require
multi-layering, I think you are going to be pissing in the wind
attempting a (commercially viable) repair without the benefit of at
least schematics
...

I would second that. I doubt the time and effort spent in attemptng
this is time and effort well spent. You'd be better off going for a
nice walk in the countryside instead, after telling your customer
this is not a viable repair. Which you or he wll end up doing
anyway.

I third that. Much as I commend the spirit of trying to fix everything
yourself that is possible, some things just aren't made to be fixed.
Multilayer circuit boards seem to be one of those things.



Yep. Just yesterday I rejected a big ol' Pioneer amp with every output
transistor short on both channels, and most of the emitter Rs open. The
mackled-up box that it came in from the customer, suggested that they
might
have obtained it from uPay or some such. With a sigh, I put its covers
back
on, and explained to the shop which took it in, that it was going to be
more
trouble than it was worth. They told me that they 'knew' this was going
to
be the case, but took it in anyway ...

I then went out for that walk in the country that Gareth suggested ...

A few years back, I would have fixed it come what may. Now, it seems that
my
time is more importantly used on jobs that actually make me some money.

Arfa

You have my sympathies. After replacing $100 worth of high power
transistors or hybrids, it doesn't leave much for labor. You would be
better off fixing cars or washing machines.

It has been my experience with consumer equipment, that if you can fix it,
the customer will either be poor and can't afford it, or will be genuinely
disappointed because they really wanted the newest, latest gimmick. If
you
fix it, they will never return to claim it. Or in one case, brought the
whole family over and while I was distracted, one snuck out with TV and
paperwork and all bolted on queue without paying.

Always leave the unit disassembled or at least with the back off with
wiring
and circuits exposed and settle the invoice before putting it back
together.
Thieves don't want to get electrocuted.


It never ceases to amaze me what antics customers will get up to. I
generally keep myself 'decoupled' from the actual equipment owners by
offering a trade repair service only. You don't make quite so much money as
you would by charging a customer direct, but at least you don't get the
hassle of having to get money out of them, or even get them to come back to
collect their pieces of ***.

Most of the places that I do work for, take a deposit which at least covers
the basic service charge that they will have to pay to me, come what may.
That ensures that neither they, nor I, are ever out of pocket on items like
the Pioneer. Of course, for various reasons, we both occasionally 'take a
hit' when one or other of us makes a bad call on ordering some parts, or
placing unfounded trust in a customer, but overall, myself and all of the
stores that I am doing work for - mostly family owned businesses well known
in the area - have been in the game long enough to be able to make valid
judgements 98% of the time.

Arfa


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