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Yamaha YST-SW800 active sub help needed

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Stefan Toftevall

Jan 1, 1970
0
Hi everyone,
I need to get in touch with someone who's familiar with Yamaha's
active sub model YST-SW800. Well, this unit features a switchmode
powersupply among with a high power class D output stage.
It came into my repairshop with blown switching transistors in the
primary (2SC4140). Replaced those and powered it up to find a high
pitched self-oscillating sound coming out of the unit. Don't know if
the sound comes from the smps or the speaker itself. Didn't dare to
run it for more than 2-3 seconds in case I blow the switch.transistors
again.
So I'm looking for any advice regarding what could be the cause of the
smps damage, like service bulletins or upgrades, or any explanation
why the unit oscillates like it does.
Any advice is warmly appreciated,
best regards
Stefan
 
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Jerry G.

Jan 1, 1970
0
Check for any high ESR or shorted caps. These do cause problems with
the output drive tansistors.

The switching supply transormer may be damaged if the switching
transistors were shorted. I have seen this before in other similiar
units.

Unless you are an authorized service rep for these products, I doubt
Yamaha will sell you the parts or service schematic. You may have to
send them the unit to have it serviced. If the unit is not a very
expensive one, it will pay to replace it.

Jerry G.
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Leonard Caillouet

Jan 1, 1970
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Once again, Jerry, you are giving advice based on general assumptions on
equipment you obviously have no specific knowledge of and misleading another
poster. Yamaha sells manuals rather inexpensively and sells parts to
anyone. Dealers and ASCs get discounts, and only ASCs get access to
training info and tech support, but you can buy nearly any of their audio
manuals for about $18 retail and their people are very helpful about looking
up part numbers.

It is unlikely that the unit is not worth repairing as it was one of
Yamaha's more expensive subs.

Leonard
 
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Mark D. Zacharias

Jan 1, 1970
0
Once again, Jerry, you are giving advice based on >general assumptions on
equipment you obviously have no specific knowledge of >and misleading
another
poster.

Amen!

Mark Z.
 
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