11-27-2012, 09:08 AM
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#1 |
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Banned
Join Date: Jul 2006
Location: Sexy Presidential Palace.
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Need Help Fixing An '80s SS Marshall!
Hey guys, I recently got a 1986 Marshall Mosfet 5213 SS amp for free
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First thing's first, safety! It was last plugged in and on about 20 hours ago. I'm assuming I need to discharge capacitors before working on this thing? What's the best way to go about this? Anyway here's the problem. Channel A is a split channel, dirty/boost, and a footswitch activates the boost. The volume on this channel is practically non-existant. It's there if I turn everything up full, but not even loud enough to play along with some music. I haven't been able to try out the boost yet as I don't have a footswitch, but I'll let you know once I do. There's no obvious soldering problems that I can see, but I haven't checked the underside of the boards, as I'm assuming it's not safe to. Here's a couple pictures of the front panel and the inside, if you need close ups of anything, let me know and I'll get some. show
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11-27-2012, 12:04 PM
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#2 |
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The song remains similar
Join Date: Nov 2006
Location: The ****ing Desert
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The biggest problem I can see is that this amp only goes up to 10. If it went up to 11, you wouldn't have any problems.
Other than that, have you checked the transformers? I had a similar problem with my old Randall and a new transformer did the trick.
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XBL - StipularAbyss17 |
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11-27-2012, 12:11 PM
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#3 |
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Banned
Join Date: Jul 2006
Location: Sexy Presidential Palace.
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I haven't checked anything yet, worried about electrocuting myself... again
 I'll keep that in mind though  |
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11-27-2012, 03:04 PM
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#4 |
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The song remains similar
Join Date: Nov 2006
Location: The ****ing Desert
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Also, you may want to adjust the "line out" Pot, that can sometimes be a problem on Marshalls.
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XBL - StipularAbyss17 |
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11-28-2012, 06:47 AM
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#5 |
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Banned
Join Date: Jul 2006
Location: Sexy Presidential Palace.
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Yeah, I've had the line out set to max anyway
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11-28-2012, 09:41 AM
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#6 |
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Call me Gordon
Join Date: May 2011
Location: Plymouth, UK
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Hey bud, first things first, take a multi meter and measure (dc) voltage on the two big blue dubilier caps, if they read below 10V you're safe to mess
Next step is to let me finish trying to debug this spec op and get on a computer with a screen I can see the pictures on
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Epiphone Les Paul Ultra-III
Jet City JCA5212RC Archer "Nuns in Poses" Distortion Archer "Dry Ice" Overdrive EHX Deluxe Memory Boy |
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11-28-2012, 09:55 AM
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#7 |
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Call me Gordon
Join Date: May 2011
Location: Plymouth, UK
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just a few clarifications:
you're experiencing no issues on channel b? the issue doesn't go away with the reverb turned off? do any of the caps look dodgy, old, or feel like they have air bubbles? EDIT: these are mainly just so i can find them easily but you may find use of them Channel A Schematic: http://drtube.com/schematics/marshall/5213a.gif Channel B Schematic: http://drtube.com/schematics/marshall/5213b.gif PSU and Power Amp: http://drtube.com/schematics/marshall/5213psu.gif
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Epiphone Les Paul Ultra-III
Jet City JCA5212RC Archer "Nuns in Poses" Distortion Archer "Dry Ice" Overdrive EHX Deluxe Memory Boy Last edited by GABarrie : 11-28-2012 at 10:00 AM. |
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11-28-2012, 10:01 AM
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#8 |
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Banned
Join Date: Jul 2006
Location: Sexy Presidential Palace.
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Okay we're safe then
 1. Channel B is perfect, the only problem was a crackly EQ pot, but that's sorted now. 2. Reverb didn't seem to make a difference at all, I can't turn it 'off' so to speak, but I've had it turned right down. 3. The only thing I can see with the caps is the green coating on one is cracking and flaking off a little. Haha, thanks for the schematics, I can spend hours struggling to decipher them |
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11-28-2012, 10:03 AM
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#9 |
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Banned
Join Date: Jul 2006
Location: Sexy Presidential Palace.
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Ahh, I may have spotted a problem. 2 minutes.
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11-28-2012, 10:05 AM
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#10 |
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Call me Gordon
Join Date: May 2011
Location: Plymouth, UK
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there are no green caps... do you mean the chunky green thing on the PSU/Power amp board that is labeled R9?
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Epiphone Les Paul Ultra-III
Jet City JCA5212RC Archer "Nuns in Poses" Distortion Archer "Dry Ice" Overdrive EHX Deluxe Memory Boy |
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11-28-2012, 10:06 AM
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#11 |
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Banned
Join Date: Jul 2006
Location: Sexy Presidential Palace.
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Clipped caps?
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11-28-2012, 10:07 AM
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#12 | |
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Banned
Join Date: Jul 2006
Location: Sexy Presidential Palace.
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Quote:
Oh yeah, woops! |
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11-28-2012, 10:15 AM
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#13 |
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Call me Gordon
Join Date: May 2011
Location: Plymouth, UK
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the side of those potentially clipped caps closest to the pots, where they sit on a trace with two diodes? can you check if that trace is ground? Continuity checker between there and say the ground bit on the input jack?
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Epiphone Les Paul Ultra-III
Jet City JCA5212RC Archer "Nuns in Poses" Distortion Archer "Dry Ice" Overdrive EHX Deluxe Memory Boy |
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11-28-2012, 10:29 AM
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#14 |
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Banned
Join Date: Jul 2006
Location: Sexy Presidential Palace.
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That seems fine, as far as I can tell.
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11-28-2012, 11:26 AM
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#15 |
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Call me Gordon
Join Date: May 2011
Location: Plymouth, UK
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hrmmm...
right, next you're gonna have to work on this whilst it's live... be careful but you know the drill, make sure the speaker is attached too or you'll fry the mosfets. I will assume you know which pins are which on an 8 pin chip so I won't explain that either. You need to measure the voltages of pins 3, 4, 6, 8 on IC1, IC2 and IC3. Do it in reference to ground so make sure your black probe is on a ground connection, then just note them down including if they are 0 or negative (the negatives are important)
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Epiphone Les Paul Ultra-III
Jet City JCA5212RC Archer "Nuns in Poses" Distortion Archer "Dry Ice" Overdrive EHX Deluxe Memory Boy Last edited by GABarrie : 11-28-2012 at 11:28 AM. |
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11-28-2012, 11:40 AM
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#16 |
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Banned
Join Date: Jul 2006
Location: Sexy Presidential Palace.
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Actually I'm not sure I'm afraid, former or latter?
 Edit: Nevermind, I've got it. 8 7 6 5 1 2 3 4 Last edited by whoomit : 11-28-2012 at 11:41 AM. |
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11-28-2012, 11:42 AM
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#17 |
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Call me Gordon
Join Date: May 2011
Location: Plymouth, UK
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neither.... on the chip there is a circle on top, thats pin one...
Code:
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Epiphone Les Paul Ultra-III
Jet City JCA5212RC Archer "Nuns in Poses" Distortion Archer "Dry Ice" Overdrive EHX Deluxe Memory Boy |
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11-28-2012, 11:59 AM
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#18 |
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Banned
Join Date: Jul 2006
Location: Sexy Presidential Palace.
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Code:
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11-28-2012, 12:08 PM
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#19 |
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Call me Gordon
Join Date: May 2011
Location: Plymouth, UK
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well balls! was hoping that would be wrong... it wasn't...
ummm... could be one of the opamps failing.... you got any tl072s lying around?
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Epiphone Les Paul Ultra-III
Jet City JCA5212RC Archer "Nuns in Poses" Distortion Archer "Dry Ice" Overdrive EHX Deluxe Memory Boy |
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11-28-2012, 12:14 PM
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#20 |
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Banned
Join Date: Jul 2006
Location: Sexy Presidential Palace.
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You mean you were hoping my values would be wrong, but they were correct?
Or you were hoping your dignosis would be wrong, but it was correct, meaning the values were incorrect? No, I don't, no ICs anywhere I'm afraid. All I've got lying around are caps and resistors. |
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