DC offset issues - Help! - Dean GA40R - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 25th May 2013, 02:36 AM   #1
Chrobo is offline Chrobo  United States
diyAudio Member
 
Join Date: May 2013
Location: Corpus Christi, TX
Default DC offset issues - Help! - Dean GA40R

I have a solid-state Dean GA40R guitar amp. When I turn it on with no inputs and all the knobs at 0 I get this huge hum/buzz coming from the speaker. The amp has been sitting for a couple of years and from what I remember, there used to be a pop or buzz sound everytime I turned it on for a split second. I don't know if that is useful information. When turned on the speaker only pushes out, which from what I have been able to gather online, means it has a DC offset. I have used a multimeter which for DC purposes can only read DCV (DC Volts) and DCmA (DC miliamps). From what I have read so far, DCmV (DC milivolts) is what I am trying to read. When I use the setting of DCV on my multimeter I get a reading off of the negative and positive speaker terminals of about 24 DCV. Would this be the the same as 2,400 DCmV? and if so, would this indicate a huge DC offset?

Also, I cant find any useful schematic info or user manuals for this amp. If anyone knows where to find some or has more info on it that would be great.

Once I figure out if this is a correct DC offset reading, where do I go from there on troubleshooting? I am pretty new to this, but am pretty interested in tinkering around with it, I have knack for repairs.

Any information is appreciated. Thanks!
  Reply With Quote
Old 25th May 2013, 03:45 AM   #2
DUG is offline DUG  Canada
diyAudio Member
 
Join Date: Jan 2003
Location: mississauga ontario canada
24 VDC is 24,000mVdc

Your speaker may be permanently damaged with this level of voltage applied.

Disconnect the speaker and put in a 100W light bulb for a load until you fix it.

24VDC is not what I would call an offset issue...I would call it broken.

A schematic would really help and you may have to try to trace the circuit out to get an idea what it is supposed to be.

Or you could get the part numbers of all of the transistors and measure the voltages on them and see if the numbers make sense with how they should be hooked up.

Hope that helps a little.

__________________
Doug We are all learning...we can all help
"You can't stop the signal, Mal. Everything goes somewhere..."
  Reply With Quote
Old 25th May 2013, 04:09 AM   #3
Chrobo is offline Chrobo  United States
diyAudio Member
 
Join Date: May 2013
Location: Corpus Christi, TX
I have a speaker of no use attached for quick on/off tests to see if the problem is still occurring.

Of the three transistors, I am only getting a reading from two. I am unsure of this reading because it spikes on my multimeter and sparks at the connection. Could the one transistor giving me no reading be the problem? or is it more likely that the underlying problem is whatever caused it to blow to begin with?

I have scoured the internet in search of a schematic. Are there any websites in particular that would be of aid?
  Reply With Quote
Old 25th May 2013, 04:24 AM   #4
Chrobo is offline Chrobo  United States
diyAudio Member
 
Join Date: May 2013
Location: Corpus Christi, TX
Well, now when I turn it on after a second I get smoke from the middle control knob and from set of wires going to the line-out and external speaker inputs. This amp might just be near death or should be taken to a professional at this point I'm assuming.
  Reply With Quote
Old 25th May 2013, 02:16 PM   #5
DUG is offline DUG  Canada
diyAudio Member
 
Join Date: Jan 2003
Location: mississauga ontario canada
When you let the smoke out usually parts need replacing.

IMHO:

Schematic or trace out the schematic OR professional for a quote.

__________________
Doug We are all learning...we can all help
"You can't stop the signal, Mal. Everything goes somewhere..."
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

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 Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Adjusting DC offset issues bugeyed Solid State 0 3rd November 2012 10:24 PM
Bose 1800: DC Offset Issues jamesdean Solid State 3 10th December 2011 03:14 AM
DH-220 Clone (SMART TA-242) can't adjust DC offset using offset bias pot? beady Solid State 6 17th March 2011 10:53 AM
DC offset issues with GC fishski13 Chip Amps 18 17th November 2009 12:33 AM
High Dc Offset Issues nic6paul Class D 2 3rd March 2009 01:49 PM


New To Site? Need Help?

All times are GMT. The time now is 12:23 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2