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Marshall cab problem (again)


Al Heeley
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Set up for the gig last night to find my 1x15 marshall extn cab had decided to play up.
I took the back panel off to find the copper coil had broken where it enters the pcb:

Now in my attempts to fix it I fear I have wrecked the inductor.
Any idea where I can get a new one?
Anyone know where I can find the spec for a new one? This is the 300W/600W 1 x 15 MBC115 cab from Marshall, bought new in Jan this year and twice let me down now. First time it was a dry solder joint on the pcb (again the copper inductor coil).
It seems the coil had never really been epoxied firmly to the pcb so it was loose to bounce about and this has evidently fatigued the copper wire and broken it.

Is this device the filter choke? To act like a big capacitor and pass the bass freqs to the main speaker cone and divert the high ones to the tweeter unit?

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[quote name='Al Heeley' post='544113' date='Jul 18 2009, 04:38 PM']Is this device the filter choke? To act like a big capacitor and pass the bass freqs to the main speaker cone and divert the high ones to the tweeter unit?[/quote]

Yeh its the inductor that forms part of the crossover LC network except it works the opposite way to capacitors.

Is there anything marked on the inductor? You can take it out of circuit and disconnecet the horn, the cab will still work just with less top end but sounds like a warranty job.

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[quote name='Al Heeley' post='544196' date='Jul 18 2009, 06:34 PM']I'll give marshall spares a call on Monday. There's no moarkings on the inductor.
I don't use the horm anyway; the 2 x 10 combo has a horn, so if I just reconnect the pcb holes with wire instead of having the inductor in place, it will run ok?[/quote]

best to just sever all connections to the crossover and horn IMO.

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It's a good powerful cab for the money (I paid £149) and adds a lot of bottom end push to the MB4210 I bought at the same time. It sounds fine for the money.
I played thru a Mesa 4 x 10 last week and it was phenomenal! I'd rather have enough money to afford higher end gear but I can't justify it so the Marshall is a good compromise. I'd get too precious lugging high end gear about the pubs and clubs every 2 weeks for gigs.
Reckon I must have just been a bit unlucky with the QC on my cab. With the inductor now binned theres hopefully very little else that can go wrong with it.

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  • 7 years later...

Only just seen this.....

First you need to unsolder the coil. There are two wires coming out of the coil. Unsolder the wire still connected to the board and also the piece of broken wire. If it's the outside wire on the coil that has broken, just pull out a piece of the wire from the winding, scrape off the insulation at the end, tin it and solder it back in place.

If it's the inside one that has snapped off (much more likely), it's a bit more difficult. You will be able to see the very end of the wire that has snapped off poking out of the coil former. Your mission, should you accept it, is to undo about one turn of that wire from the inside of the coil so that you can resolder it to the board. Use a very thin screwdriver to ease the wire out enough to be able to grab it with some snub nosed pliars. If that proves too difficult, use your snips to cut the plastic bobbin so that you can access that bit of wire and pull it out. Cutting the plastic won't do any harm. Also bear in mind that the insulation on the wire is quite tough, but don't go mad.

I've done this loads of times. Good luck! Oh yes - glue the coil back with silicon sealant and a couple of tie wraps. Otherwise the same thing will happen again next week. :)

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