"Gareth Magennis" wrote in message
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"Arfa Daily" wrote in message
...


"Gareth Magennis" wrote in message
...

"N_Cook" wrote in message
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Arfa Daily wrote in message
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"Stephen Birchall" wrote in message
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After reading all of the issues regarding the aforementioned mixer,
I
decided I had nothing to loose by taking it to pieces and attempting
to test the power output stage. On dismantling all of the plug in
units, it became apparent that both of the output boards had come
loose either by shock or vibration despite being held in by
crosshead
screws. After testing the transistors, which were OK, I plugged
everything back in a couple of times to clean the contacts and hey
presto, I now have a fully functioning unit again. So it is
sometimes
best to try the simple things first, before spending a fortune.
(previously an electronics engineer had told me it would cost approx
£250 to fix because on his inspection, one of the channels had been
fried. I shan't be recommending him to anyone!)


Nail polish is very good for stopping screws coming loose. Just put a
dollop
around the head of the screw, and onto the surface that it's screwed
against. Very convenient as it is in a small bottle with its own built
in
brush. It dries very quickly, and will proof the screw or nut against
coming
loose by vibration, whilst still allowing for an easy 'break' of the
seal
with a screwdriver. Also good for sealing preset pots against
vibration
movement, or tamper-proofing them.

Arfa


Thats what I use on these Stagepas amp subunits, requires a long thin
brush
to apply it. Would be nice to know from the OP whether the screws just
undid
or is the plastic thread part stripped ? ie larger screws needed, even
if
length is cut down, to give bite

As for 75 squid from Yamaha just shows the advantage to component-level
repair




The £75 included a reasonably healthy mark up to the price I paid, which
was probably around £55.

You have to judge whether, if you did repair to component level, the
customer would pay more or less for your services, and how more or less
reliable this module would subsequently be.

My judgment, in this case, was to go for the ultimate reliability of all
new parts, and I figure the extra few quid on top of the labour and
parts I would have charged for component level repair was in the
customer's best interests.

Plus it would not come back like a boomerang covered in dingo poo,
costing me time and reputation.



Cheers,


Gareth.


Ah, but is a new board *actually* more reliable than an old one properly
repaired ? I've just been having this argument with one of my customers.
Bathtub curves etc would suggest not ... :-)

Arfa



Dunno, but one that has had a catastophic failure at high power may well
have damaged or weakened components that may fail some time later.

You would have to specifically conduct a proper test of blown up Yamaha
Power Amp Modules, and see whether repaired ones do, or do not, last
longer than a new original. And of course it would depend who has
repaired it.
This is not a typical type of PCB or circuitry, its a bit of a special.

I doubt very much that data is out there, so you pays your money and takes
your choice!


Cheers,


Gareth.


Actually, in the case of these dreadful little amps, I am with you, and I
think that a replacement board is the way to go when there has been a
catastrophic failure. My recent experience involved a main board from a
vending machine. I had been asked by a customer that I repair a lot of other
modules for, to look into repairing these items, and a number of faulty ones
had been sent to me for evaluation. I had spent some time on the project
studying the very limited service information for the machine, to work out
what all the considerable number of inputs and outputs were for, and how to
load and stimulate these to fool a board into thinking that it was installed
in a working machine. I had already established that at least half of the
boards that had been sent for evaluation, had a single failed triac on them,
so they would potentially have been a nice little earner.

Then, all of a sudden, the customer comes back to me, and says that the
project has been called off, because their customer, who has a very great
deal of these machines installed in their premises, wants only brand new
boards as replacements, and is not prepared to accept boards that have been
repaired. I asked why this was, and the answer that I got was that they felt
that new boards would be more reliable. No matter how much that I pointed
out that the real life evidence of bathtub curves and infant mortality,
clearly refuted that premise, they were not having any of it. They seemed
unable to understand that a board that has been in service for a while has
passed the infant mortality stage, and is fully burnt in. And that it is in
the main phase of its service life, where any problems are likely to be
random single component failures. None of the parts on this board were
specials, so it could have been repaired to full manufacturer's spec, using
original manufacturer's parts. In fact, the triac that seemed to be failing
could actually have been upgraded to the next one in the series to *improve*
overall reliability.

But here's the really silly bit. Another board in the machine, which I
already repair for them, suffers a faulty tactile switch on a regular basis.
So I asked if they were going to stop having that repaired as well. Oh no,
they said. We can carry on doing that one, because it's only a replacement
switch. Slowly banging my head on the bench, I asked them why they felt that
replacing that single switch was any different from replacing a single
triac, and how they felt that a board that was repaired by having that
switch put in, would be any more reliable than a board that had been
repaired by having a triac put in it. There was no answer, because they
really couldn't see the logic ...

To be fair, the guy that I deal with direct, was with me on this, but his
hands were tied from further up the food chain. What bothers me most is what
happens to all of the faulty boards. Do they just become scrap destined for
landfill ? Bit of a waste ...

Arfa