Music Electronics Forum

Go Back   Music Electronics Forum > Amplification > Other Amps

Reply
 
LinkBack Thread Tools Display Modes
Old 10-31-2009, 10:48 PM   #1
Junior Member
 
Join Date: Oct 2009
Location: michigan
Posts: 7
marshall vs100 blown fuses

ok when i got the amp it didnt work and it time to fix it. well i found out that i have an electrical problem in the output curcuit. well i just reasently took out t1 from the curcuit and it still blow the fuse so i know the problem isnt after T1 (transister 1) and i was wondering what to check next. i can find a shematic for you at this web site http://www.drtube.com/schematics/mar...v100-62-02.pdf
please help me
donnie
guitardude10890 is offline   Reply With Quote
...and now, a word from our sponsor:
Old 11-01-2009, 01:43 AM   #2
Senior Member
 
Jazz P Bass's Avatar
 
Join Date: Dec 2008
Location: Wernersville, PA
Posts: 728
T1 differential pair

With the power off try testing T9,T10 & T11,T12 for a shorted condition.
These are the output transistors.
T1 is 1/2 of the differential pair input stage.
Jazz P Bass is offline   Reply With Quote
Old 11-01-2009, 09:09 PM   #3
Junior Member
 
Join Date: Oct 2009
Location: michigan
Posts: 7
i tested T9 T10 T11 and T12 and they all checked out fine what eles should i check
guitardude10890 is offline   Reply With Quote
Old 11-01-2009, 10:11 PM   #4
Senior Member
 
Jazz P Bass's Avatar
 
Join Date: Dec 2008
Location: Wernersville, PA
Posts: 728
Power supply check

I would start at the beginning.
The lower part of the schematic is the power supply.
There is also the preamp to consider. That is where the tubes are.
The IC's need + - 15 volts.
Check T 13,14 & 15 of the power supply.
All the diodes, specifically the bridge rectifier.
It looks like Conn 14 can be disconnected. If so disconnect it from the rest of the amp. That is your high voltage rails.
I do not know what equipment you have. A variac would be nice. An ammeter in series is always good.
Short of that a 60 watt lamp in series with one of the AC legs will help.
Attached Files
File Type: pdf v100-60-02.pdf (154.4 KB, 8 views)
Jazz P Bass is offline   Reply With Quote
Old 11-02-2009, 03:52 PM   #5
Junior Member
 
Join Date: Oct 2009
Location: michigan
Posts: 7
ok i still need to test T 13 14 and 15 i already know all the diodes are good because thats the one of the first things i did and their all good and my dad put a new bridge rectifier in it so i know thats good so ill get on testing T13 14 15 thanks again Donnie T
guitardude10890 is offline   Reply With Quote
Old 11-04-2009, 12:29 AM   #6
Junior Member
 
Join Date: Oct 2009
Location: michigan
Posts: 7
i have tested T13 14 15 and they all look good this thing is being a pain
guitardude10890 is offline   Reply With Quote
Old 11-04-2009, 12:47 AM   #7
Senior Member
 
Jazz P Bass's Avatar
 
Join Date: Dec 2008
Location: Wernersville, PA
Posts: 728
Testing A Power Amplifier

At this point you have to back up.
You have the schematic, right.
Start at the beginning.
Disconnect the load off of the power supply.
+L & -L are on one connector.
Disconnect it.
Power up the amp & check +L & -L.
These are your high voltage rails.
If o/k, move on to the IC voltages. +15Vdc & -15Vdc.
If o/k then you have to find exactly what is "loading down" the power supply.
Start there.
Isn't this Fun!
Jazz P Bass is offline   Reply With Quote
Old 02-17-2010, 01:36 AM   #8
Junior Member
 
Join Date: Oct 2009
Location: michigan
Posts: 7
hey everyone i have found the problem with my amp and now i need to get a new transistor for it. does anyone know where i can get transistor 12 on the schematic
http://www.drtube.com/schematics/mar...v100-62-02.pdf
if you can help please do thanks
guitardude10890 is offline   Reply With Quote
Old 02-17-2010, 04:35 AM   #9
Senior Member
 
Jazz P Bass's Avatar
 
Join Date: Dec 2008
Location: Wernersville, PA
Posts: 728
BDV64

I find it highly unlikely that the one output transistor is all that is wrong.
I would check all around that area.
Resistors, transistors.
Here is a link for the BDV64
FindChips.com Search
Attached Files
File Type: pdf v100-62-02.pdf (84.5 KB, 4 views)
Jazz P Bass is offline   Reply With Quote
Old 02-17-2010, 09:56 AM   #10
Senior Member
 
Join Date: May 2006
Location: Lansing, Michigan, USA
Posts: 10,258
Replace a BDV64 with TIP147. Replace its mate. The two BDV65s can be replaced with TIP142.
__________________
Education is what you're left with after you have forgotten what you have learned.
Enzo is offline   Reply With Quote
Old 03-07-2010, 08:16 AM   #11
Junior Member
 
Join Date: Oct 2009
Location: michigan
Posts: 7
i have replaced all four output transistors and now the amp will turn on but all im getting out of it is a loud humming noise what would you suggest i do?

and again thank you for all the help.
guitardude10890 is offline   Reply With Quote
Old 03-07-2010, 10:57 AM   #12
Senior Member
 
Join Date: May 2006
Location: Lansing, Michigan, USA
Posts: 10,258
It is still putting DC on the speaker most likely. Pull the wires off the speaker and check if there is substantial DC there.

I'd be checking T6,7,8, and R12-15, at least.
__________________
Education is what you're left with after you have forgotten what you have learned.
Enzo is offline   Reply With Quote
Old 03-07-2010, 11:58 AM   #13
Junior Member
 
Join Date: Oct 2009
Location: michigan
Posts: 7
i checked the out put and had 38v dc and resistor 12-15 are good and transistor 6 looks good ill have to check the other 2 later
guitardude10890 is offline   Reply With Quote
Old 03-07-2010, 04:58 PM   #14
Member
 
Join Date: Sep 2008
Posts: 27
If T12 was bad, make sure that R19 is still good. in fact check R24 and R15 also.

I have repaired many amps where just one output transistor has gone bad!
zero cool is offline   Reply With Quote
Old 03-08-2010, 08:00 PM   #15
Member
 
Join Date: Sep 2008
Posts: 27
Quote:
Originally Posted by guitardude10890 View Post
i am getting 0.00 ohms on r19 r24 r25 and r21

Those resistors are .33 ohms so set your meter to the lowest scale possible. with the lead resistance added in you will probably see something like .6 ohms that's ok, just make sure they are not open or some value above 1 ohm.
zero cool is offline   Reply With Quote
Reply

Bookmarks

« Mackie SRM450 | - »

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

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

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
jcm 900 no sound blown OPV fuses augie1 Maintenance, Troubleshooting & Repair 6 09-08-2009 01:42 AM
Marshall VS100 blowing fuses brokenbones Maintenance, Troubleshooting & Repair 22 05-03-2009 01:15 PM
Blown Fuses Matthenoz Maintenance, Troubleshooting & Repair 1 03-15-2008 01:44 AM
Need help trouble shooting blown fuses in solid state amps! srvprodigy Repair and Restoration 10 02-05-2008 02:18 AM
Looking for Marshall VS100 schematic methodofcontrol Maintenance, Troubleshooting & Repair 5 06-27-2007 01:11 AM


All times are GMT +1. The time now is 02:45 PM.


Powered by vBulletin   Copyright ©2000 - 2010, Jelsoft Enterprises Ltd.
Content Relevant URLs by vBSEO