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Wharfdale pm700 pa schematic?

Started by nosaj, September 08, 2014, 07:21:41 PM

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nosaj

Same volume, rec out sounds normal.

Looking at pcb board side it appears a njm4558l was snipped out and there was tone on one of the pins but no others. so being a Operational Amplifiers - Op Amps Dual High Gain. I think I can stop here until I can order one in.

This pa was given to me in an unknown state so anything done to it is unknown.

Will follow up when part comes in.

Thanks,
Jason

Roly

Quote from: nosajit appears a njm4558l was snipped out

Ahhh HA!  The old "no op-amp" trick will do it every time.   ::)

Just about any pin-compatable dual op-amp will replace that (and most will do a better job, i.e. TL072, LM833, etc.)

Keep us posted with how you get on.   :dbtu:
If you say theory and practice don't agree you haven't applied enough theory.

nosaj

Never having dealt with a sip-8 package. Ill definately have to order some. Wasn't a package I was familar with so it didn't stick out visually.

Thanks for your help ill keep you updated.
Jason

Roly

SIP versions are harder to get around here, so I'd be looking at a DIP on a tiny Vero sub-board.
If you say theory and practice don't agree you haven't applied enough theory.

nosaj

Mouser has them for like.76 cents ea US.

Roly

Not "impossible" just harder because they are generally only stocked by manufacturers' service departments, not by the main component suppliers.  DIP?  SMD?  Sure, but not SIP.

Quote from: nosajMouser has them for like.76 cents ea US.

And it costs $60 to post a small empty cardboard box from the US to Australia.  $60.76 - cheap!   :lmao:

Keep us posted on how you get on.
If you say theory and practice don't agree you haven't applied enough theory.

J M Fahey

I was going to suggest something similar.
What I do in such cases (Argentina is same as Australia in all the bad ways :( ) is search for a guy , a regular Tech who works at home or in a small shop, not the mighty Yamaha or Roland main service center (who won't even talk to me) who repairs standard Japanese Hi Fi stuff.
Say CD players, VCR, TV, Home Audio in general.
He certainly has found a way to get Japanese parts, including very popular , common as dirt SIP njm4558 , which is used everywhere.
Worst case, one can be cannibalized from a dead junk pile unit.

He won't charge U$0.79 for it, but probably either :"hey, just pick it up and get away from here ;) " or "go to the street corner shop and get a couple beers" .
Or he might ask for similar value, say ... "is $5 right for you?"

Somebody here (Enzo? ... Roly?)  once mentioned using a dead Yamaha receiver or something similar for a seemingly inexhaustible supply of Japanese parts.

Roly

Must have been Enzo ('tho I'm sure I have a board something like that somewhere in my pile ... but don't we all?).  ;)
If you say theory and practice don't agree you haven't applied enough theory.

g1

  Thrift shops can be very cheap sources of consumer electronic items to be used for parts.

nosaj

Update on wharfdale i was able to get another broken one and subbed the preamp from it. It is now working intermittantly.
Sometimes it takes 2 or 3 flips of on/off toggle to turn it on all the way(everytime the psu fans come on) It is a smps I have recapped the power supply as it was loaded with the capxcom counterfit caps.  i believe that it is a rail that is failing to come up but not sure how to go about it without a schematic.

Thanks,
nosaj