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Old 03-11-2014, 02:56 AM   #1
Slayterica
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selling a broken marshall question

ok so I have a marshall jcm 900 slx that I purchased for 300 dollars. I was told it just needed new tubes and a slight touch up. I found out later some of the knobs do not work correctly, among other things; it was apparently dropped on its face. so it needs about $300 of repairs, quote from sam ash. I do not have the cash for repair nor do I have any need for the amp, I just got a mesa boogie.
if I try to sell this on craigslist, what would be a fair price, like 200-300, or is that too much? Its busted so idk what would be fair
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Old 03-11-2014, 03:05 AM   #2
Cathbard
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It's not that hard to replace the pots on those, you do have to partially remove the PCB to do it but it isn't a particularly hard job to do if you can solder. $300 would be including labor. Pots **** up on JCM's all the time.
And tubes are pretty easy too, you can get the bias in the ballpark with just a multimeter and a screwdriver.
Do those things and you'll be able to get top dollar for it.
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Old 03-11-2014, 03:22 AM   #3
Slayterica
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I was afraid you say that. I dont know the first thing about amps. I can solder pickups thats about it. wouldnt know where to start
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Old 03-11-2014, 03:59 AM   #4
7thString
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Quote:
Originally Posted by Slayterica
I was afraid you say that. I dont know the first thing about amps. I can solder pickups thats about it. wouldnt know where to start

Start reading! I honestly think you could fix it up yourself within a couple of weeks of learning / sourcing parts etc. hell - I'd buy it off you for $300 if I didn't already own a ridiculously loud marshall (I say ridiculous becuase with my current living situation I have to drive to a farm to play the thing). Anyway I think you should at least attempt the DIY fix, much to learn and you'll surprise yourself with what you can accomplish.
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Old 03-11-2014, 04:15 AM   #5
Slayterica
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alright man you talked me into it. ill give it a try. dammit hah
any tips or references?
thank you btw
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Old 03-11-2014, 07:16 AM   #6
7thString
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Good for you man. The Eurotubes website https://www.eurotubes.com/ is a great place to start, and there are a lot of helpful people such as Cathbard and 311 who regularly comment in GG&A who could help you with any specific questions. I'm guessing it would be wise to replace all the tubes if you haven't done so already, then figure out which pots are not working and either use some contact cleaner on them (on the inside) and/or replace them completely if necessary. Also inspect for other damage / loose parts from the impact when it was dropped. But before all this you should read about amp safety and how to remove it safely from the box etc. I found this quite helpful http://profile.ultimate-guitar.com/...HJH/blog/80083/
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Old 03-11-2014, 07:38 AM   #7
Cathbard
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Don't forget to unplug it before you pull the chassis.
While pulling out the chassis don't let you fingers get inside there. The outside of the chassis is ok, some internal contacts may contain voltage.
Sit the chassis on something solid at each end, like two piles of phone books or something. something taller than the tubes. Unnerstand?
Locate the filter capacitors. They're the big cylindrical cans near the power transformer. You need to discharge them.
You are supposed to use a resistor, say, 1k to 10k across the two terminals. You can do it with a piece of wire too but there's a chance you can weld the wire to the capacitor lead, which is a pain in the arse. I've got the knack of it over the years. I use a multimeter probe and very quickly swipe it across the lead barely touching it to get a spark, then I can just touch it to finish it off. But I'm an old hand. A resistor is the right way, sparks are bad, yada yada yada. I like sparks.

After you've done that the amp is safe to work on.

You'll have to undo all the pots, they're mounted on the same board. You'll work it out, it's pretty obvious really once you get started as to what comes off so you can get at the solder side on the bottom of the board.
The board in the SL/X isn't that big. It shouldn't be too hard.

But big hint. TAKE PHOTOS. At every stage, snap a shot so you can look back at it later and see what it actually looked like. The digital camera is a technician's cornucopia. Brilliant tool.



As for the tubes. Go JJ all the way. When you get to doing the power tubes I can explain the quick and easy bias method for them. How you'd do it at a gig, for example. Good enough for sale anyway.
That's an EL34 version, yes?




Edit:
Prediction. You will fix it and then go, "holy ****, this thing kicks arse!" And you won't want to sell it. SL/X's rock.
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Gilchrist custom guitar
Yamaha SBG500
Telecaster
Randall RM100
Abbey Harmonic II
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Marshall 1960A
Boss GT-100


Cathbard Amplification

Last edited by Cathbard : 03-11-2014 at 07:46 AM.
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Old 03-11-2014, 11:48 AM   #8
Slayterica
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yes I believe its el34
and thank you both gentlemen, ill do my best in the coming weeks.
but first loads of research
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Old 03-11-2014, 02:36 PM   #9
Cathbard
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Then in the power amp use JJ EL34L. Massive sounding tube. Quite an improvement on the standard EL34.
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Gilchrist custom guitar
Yamaha SBG500
Telecaster
Randall RM100
Abbey Harmonic II
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Marshall 1960A
Boss GT-100


Cathbard Amplification
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