Quad L-ite Sub (wharfedale sw-300) rustling

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Graemedench

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Joined 2004
#1
My Quad sub has started playing up.

We actually thought our next door neighbor fell down the stairs when it failed!

The sub started thumping itself and now makes loud rustling sounds.

I've taken the amp PCB out and I'm going to check the Capacitors in case they have dried out and also check / re-flow the soldering.

Any hints or tips on where else to look?

Thanks

Graeme
 
#3
Thanks.

I've just re-flowed the whole board. No Luck. So I guess I'm down to components now. ah well. I might drop quad a line and check the prices of repair. (I'm re fitting my kitchen and if its cheap enough might be worth just sending it off) I've checked all pots so caps and resistors next I guess. then Transistors.

Graeme
 
#6
Some pictures of the board may help us suggest further things. Also how was it connected up, via line inputs or speaker level?

How experienced would you say you are, eg would you be OK measuring things with a multimeter?
 
#7
Hi

I'll get some pics up tomorrow. no problem with multimeter or scope I have 2 scopes. I could given enough time figure out the amp stage but its really not my forty. Given some pointer where to look would be a massive help. It was hooked up at line level but no signal going through. I will disconnect the line feed to the main amp board and double check it is the power stage faulting (preamp is on another board) Unfortunately the capacitance section on my meter has failed so that's not going to help much 🙁

I'll take a few pics and get them up.

Pointers are very much appreciated.

Many thanks
 
#10
Hi Yes to both. I'm sure I have something in my parts bins I can replace at least for testing 🙂 I'll check it out this afternoon and report back. I'm sure I have caps with enough voltage rating probably not capacitance but I'll swap the pair for testing and pull the diodes and test out of circuit. Thanks for the Interest and help.


G
 
#11
No problem 🙂 Maybe consider replacing the 4 diodes with a GBPC type rectifier bridge module, bolted to the back plate.

I'd expect the caps are 80V rated - if not, they should be with +/-65v rails ! Anything would do for testing, just less capacitance will give it less "oomph" when being driven
 
#12
Diodes seem ok I need to get replacment caps as i dont have something to swap them with. so thinking of elna from ebay? I cant seem to find direct replacments from rs or cpc and swapping the diodes out for MBR10100.

I'm off for another hunt in my parts bins 🙂

Any thoughts?
 
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#13
Hunt over but nothing high enough voltage rating lots of 63V but nothing over 🙁

I've taken the caps of but my only concern is they're all crapcons

I've noted the part numbers of the other transistors on the board attached to the heatsink

we have 2 * c4883 and 1* a1859a
 
#14
That'll be 2SC4883/2SA1859 - TO-220 driver transistors from Sanken. The extra 2SC4883 is probably serving as a bias regulator.

You are right, gets awkward once you get over 63V, ordinarily i'd recommend Panasonic TSHA or TSUP series. Digikey do have them, but i've no idea what they charge for shipping to the UK.

eBay should be fine but stay away from Chinese/HK sellers who are highly likely to be selling counterfeit parts.
 
#17
Hi Chaps.

OK I swapped the main caps out and no change. But.. just as I finished testing the fuse popped 8A Time delay on one side. I was about to swap out the diodes from one rail to the other next but I need to pick up some more fuses.

I think it popped because I didn't have the speaker plugged in and it didn't like it ..

So fuses and diodes next I guess.
 
#19
Ok Parts arrived - installed - fuses pop.

I think its possible I've been an ar** and one of the mica insulators on the outputs was missing and I may have blown them. Need to focus (going between tiling kitchen and trying to sort this) any hints on testing the outputs? I take its a case of take them out and them meter across them?

I should have just sent it to quad tbh but I should be more than capable of doing this. Just distracted.

Graeme
 
#20
The Sanken output transistors are just ordinary power transistors, so yeah, you can diode test them as you would any other transistor. You likely have some shorted C-E now. Oops 🙁

Also check the driver transistors Q13 and Q17.

A good tip for working on power amps - build a cable which has a 60-100w incandescent (filament) bulb in SERIES with the Live wire. This acts as a current limiting device. Normally you should see a brief flash as the capacitors charge, then a dull glow. If the bulb lights brightly, something is trying to draw a lot of current, and the bulb will drop most of the voltage, protecting the circuit.

Powering Up Your Radio Safely With a Dim-bulb Tester
 
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