Andrew Erickson wrote in message
...
First off, I don't have any experience with this particular piece of
gear, and not a whole lot of experience in general. Still, for what
it's worth...
In article ,
"N Cook" wrote:
Anyone familiar with these sort of tiny compact units ? any pitfalls ?as
its
the first of this type of miniature kit I've dealt with.
Not possible to play around with it without disassembling as, all
wrapped
inside one another.
Marked all the bits of celluloid and sub-assemblies before
disassembling.
No obvious solder problems or wobbly bits under illuminated mag glass.
The power board with 2 fans is confusing because what looks like 2
channel
power amp farthest from the mains inlet filter chokes is a very
distributed
SMPS, split into 2, especially with a thermistor on a vaned heatsink
with a
7 pin TO220 device either side, that look like TDA... monolithic audio
o/p
blocks.
But those devices are TOP249YN smps drivers.
The compact lump nearest the mains inlet, that looks like a compact
SMPS,
contains 4 TO220 devices , 2 being ST P14NF12FP 120V 14A mosfets and
presumably 2 matching , shrouded unseen, complements , whetever they
are -
you'd think it would be easy on the ST site to find this basic info.
It's quite possible that the power amp is essentially similar to an
SMPS; that's not too uncommon on fairly recent PA gear. It beats having
to heft about a (relatively) enormous and heavy power transformer and
heatsinks.
Any advice before replugging everything spread out on the bench and then
powering up on Monday with a twiddle stick.
Most--maybe even all--intermittent faults I've seen on PA gear is due to
the usual suspects of connectors, pots, etc. and their connections to
the circuit board. Too many cheap mixers tend to use solder connections
as mounting brackets. One particular cheap tabletop mixer I saw had an
external wall wart supply, the jack for which was held in place only
with its solder connections. It didn't take long to become loose.
Also, it probably goes without saying, but you have tried a known good
cable connected to the channel externally, right? Microphone and
instrument cables take quite a beating; they are by far the number one
cause of trouble in my experience, and luckily usually pretty easy to
repair.
--
Andrew Erickson
"He is no fool who gives what he cannot keep to gain that which he cannot
lose." -- Jim Elliot
Generally i would say this was well constructed except for the conical
greyish silver solder points. Perhaps 1Kg of the overall 2.5Kg is the weight
of the thick steel top fascia plate and the robust black enclosure box of
composite/plastic/rubber or whatever thick and dense formulation.
One potential problem, as you say, is all the pots are pcb mount only with
no bush nuts to that nice steel fascia, i've checked the dual master one
with DVM but seems ok.
I don't know what the electrical/electronic term is but in nuclear power -
the "void coefficient " could be a problem. 2 fans , 1 1.5 inch and the
other 2 inch . If either of those stopped with all that power consumption in
a small space , I wonder what the result would be. Hopefully the thermistor
would initiate a shut-down procedure.
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/