Go Back   UG Community @ Ultimate-Guitar.Com > Instruments > Gear Building & Customizing
User Name  
Password
Search:

Reply
Old 11-27-2012, 09:08 AM   #1
whoomit
 
whoomit's Avatar
 
Join Date: Jul 2006
Need Help Fixing An '80s SS Marshall!

Hey guys, I recently got a 1986 Marshall Mosfet 5213 SS amp for free

show


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
__________________
whoomit is offline   Reply With Quote
Old 11-27-2012, 12:04 PM   #2
Whiteboy_az
The song remains similar
 
Whiteboy_az's Avatar
 
Join Date: Nov 2006
Location: The ****ing Desert
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.
__________________
show


XBL - StipularAbyss17
Whiteboy_az is offline   Reply With Quote
Old 11-27-2012, 12:11 PM   #3
whoomit
 
whoomit's Avatar
 
Join Date: Jul 2006
I haven't checked anything yet, worried about electrocuting myself... again

I'll keep that in mind though
__________________
whoomit is offline   Reply With Quote
Old 11-27-2012, 03:04 PM   #4
Whiteboy_az
The song remains similar
 
Whiteboy_az's Avatar
 
Join Date: Nov 2006
Location: The ****ing Desert
Also, you may want to adjust the "line out" Pot, that can sometimes be a problem on Marshalls.
__________________
show


XBL - StipularAbyss17
Whiteboy_az is offline   Reply With Quote
Old 11-28-2012, 06:47 AM   #5
whoomit
 
whoomit's Avatar
 
Join Date: Jul 2006
Yeah, I've had the line out set to max anyway
__________________
whoomit is offline   Reply With Quote
Old 11-28-2012, 09:41 AM   #6
GABarrie
Call me Gordon
 
Join Date: May 2011
Location: Plymouth, UK
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
__________________
Epiphone Les Paul Ultra-III
Jet City JCA5212RC
Archer "Nuns in Poses" Distortion
Archer "Dry Ice" Overdrive
EHX Deluxe Memory Boy
GABarrie is offline   Reply With Quote
Old 11-28-2012, 09:55 AM   #7
GABarrie
Call me Gordon
 
Join Date: May 2011
Location: Plymouth, UK
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
__________________
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.
GABarrie is offline   Reply With Quote
Old 11-28-2012, 10:01 AM   #8
whoomit
 
whoomit's Avatar
 
Join Date: Jul 2006
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
__________________
whoomit is offline   Reply With Quote
Old 11-28-2012, 10:03 AM   #9
whoomit
 
whoomit's Avatar
 
Join Date: Jul 2006
Ahh, I may have spotted a problem. 2 minutes.
__________________
whoomit is offline   Reply With Quote
Old 11-28-2012, 10:05 AM   #10
GABarrie
Call me Gordon
 
Join Date: May 2011
Location: Plymouth, UK
there are no green caps... do you mean the chunky green thing on the PSU/Power amp board that is labeled R9?
__________________
Epiphone Les Paul Ultra-III
Jet City JCA5212RC
Archer "Nuns in Poses" Distortion
Archer "Dry Ice" Overdrive
EHX Deluxe Memory Boy
GABarrie is offline   Reply With Quote
Old 11-28-2012, 10:06 AM   #11
whoomit
 
whoomit's Avatar
 
Join Date: Jul 2006
Clipped caps?

__________________
whoomit is offline   Reply With Quote
Old 11-28-2012, 10:07 AM   #12
whoomit
 
whoomit's Avatar
 
Join Date: Jul 2006
Quote:
Originally Posted by GABarrie
there are no green caps... do you mean the chunky green thing on the PSU/Power amp board that is labeled R9?

Oh yeah, woops!
__________________
whoomit is offline   Reply With Quote
Old 11-28-2012, 10:15 AM   #13
GABarrie
Call me Gordon
 
Join Date: May 2011
Location: Plymouth, UK
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?
__________________
Epiphone Les Paul Ultra-III
Jet City JCA5212RC
Archer "Nuns in Poses" Distortion
Archer "Dry Ice" Overdrive
EHX Deluxe Memory Boy
GABarrie is offline   Reply With Quote
Old 11-28-2012, 10:29 AM   #14
whoomit
 
whoomit's Avatar
 
Join Date: Jul 2006
That seems fine, as far as I can tell.
__________________
whoomit is offline   Reply With Quote
Old 11-28-2012, 11:26 AM   #15
GABarrie
Call me Gordon
 
Join Date: May 2011
Location: Plymouth, UK
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)
__________________
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.
GABarrie is offline   Reply With Quote
Old 11-28-2012, 11:40 AM   #16
whoomit
 
whoomit's Avatar
 
Join Date: Jul 2006
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.
whoomit is offline   Reply With Quote
Old 11-28-2012, 11:42 AM   #17
GABarrie
Call me Gordon
 
Join Date: May 2011
Location: Plymouth, UK
neither.... on the chip there is a circle on top, thats pin one...


Code:
1 o 8 2 7 3 6 4 5
__________________
Epiphone Les Paul Ultra-III
Jet City JCA5212RC
Archer "Nuns in Poses" Distortion
Archer "Dry Ice" Overdrive
EHX Deluxe Memory Boy
GABarrie is offline   Reply With Quote
Old 11-28-2012, 11:59 AM   #18
whoomit
 
whoomit's Avatar
 
Join Date: Jul 2006
Code:
IC 1 IC 2 IC 3 Pin 3 -0.07 -0.06 0 Pin 4 -15.26 -15.41 -15.48 Pin 6 -0.07 0 0 Pin 8 15.22 15.44 15.44
__________________
whoomit is offline   Reply With Quote
Old 11-28-2012, 12:08 PM   #19
GABarrie
Call me Gordon
 
Join Date: May 2011
Location: Plymouth, UK
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?
__________________
Epiphone Les Paul Ultra-III
Jet City JCA5212RC
Archer "Nuns in Poses" Distortion
Archer "Dry Ice" Overdrive
EHX Deluxe Memory Boy
GABarrie is offline   Reply With Quote
Old 11-28-2012, 12:14 PM   #20
whoomit
 
whoomit's Avatar
 
Join Date: Jul 2006
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.
__________________
whoomit is offline   Reply With Quote
Reply


Thread Tools Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump



All times are GMT -4. The time now is 12:36 AM.

Forum Archives / About / Terms of Use / Advertise / Contact / Ultimate-Guitar.Com © 2014
Powered by: vBulletin Version 3.0.9
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.