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