Lightning Audio B250.1 very low output and distortion - diyAudio
Go Back   Home > Forums > General Interest > Car Audio

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 11th November 2007, 05:11 PM   #1
spooney is offline spooney  United States
diyAudio Member
 
Join Date: Dec 2006
Default Lightning Audio B250.1 very low output and distortion

A guy at work gave me this amp for making some repairs for him.Right away i noticed the power input terminals were trashed and the 12 volt leg was even pulled right out of the board.After replacing that the amp powered up fine and even played cleanly up to a certain level.After turning the volume up so far on my source unit I started to get some static like distortion that was in unison with the bass in the song i was playing.I ran a sine wave through the amp and was only able to get approximately 1.8 volts ac on the speaker outputs of the amp which is way low.I'm not getting any shorts on the output transistors so I'm thinking the problem lies somewhere in the preamp section.I was hoping maybe someone could tell me if that even sounds feasible. I know this amp is worth next to nothing even working but If I can fix it cheaply I will.If not I'll start scrapping parts out of it as I need the TIP35 and 36C's that are in the output section for another amp I have laying around.
  Reply With Quote
Old 11th November 2007, 06:04 PM   #2
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Did you confirm that you have both plus and minus rail voltage on the output transistors AND plus and minus regulated voltage (15v) on the op-amps?

Have you tried moving all controls to make sure they're not between positions and not dirty/intermittant?
  Reply With Quote
Old 11th November 2007, 06:22 PM   #3
spooney is offline spooney  United States
diyAudio Member
 
Join Date: Dec 2006
I did move all of the controls i have not however confirmed rail voltage.Can you refresh my memory and explain how to check the rails?
  Reply With Quote
Old 11th November 2007, 06:33 PM   #4
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Black lead on the transformer's secondary center tap.

To check the rail voltage, the red lead goes to the center leg of the output transistors. I would expect approximately 35v. Confirm that you have voltage on all output transistors.

For the regulated supplies, the red lead will go to pins 8 and 4 of the op-amps (for 8 pin op-amps). You should confirm that you have voltage on all of the op-amps.

You should also check the resistance between the RCA shield and the secondary center tap. It should be ~0 ohms.
  Reply With Quote
Old 11th November 2007, 07:32 PM   #5
spooney is offline spooney  United States
diyAudio Member
 
Join Date: Dec 2006
Resistance between secondary center tap and rca shield is at 0 ohms.One side of the amp the outputs transistors are at 43 volts and the other side of the amp the outputs are at -43 volts. On all 8 pin op amps I have either + or - 14.6 volts on pins 8 and 4. I'm assuming these are all dc voltage.
  Reply With Quote
Old 12th November 2007, 12:59 AM   #6
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
If all of the supplies are OK, you could have a defective op-amp or the muting circuit may be engaged.

To find a defective op-amp, you'd need some way to trace the signal through the amp to see where it became distorted.

If you could find and remove the muting transistor, you would be able to determine if the audio section is defective or if the muting circuit was not releasing the clamp on the audio signal. I don't know anythig about these amps so I can't tell you precisely where to look for the muting transistors. They are typically found where the preamp signal (from the input/crossover/equalization circuit) goes to the power amp section. One terminal is typically connected to the secondary ground. The base of the transistor will be driven by a transistor or opto-coupler near the power supply.
  Reply With Quote
Old 13th November 2007, 01:06 AM   #7
spooney is offline spooney  United States
diyAudio Member
 
Join Date: Dec 2006
is there any way to test voltages on the other pins of the op amps to determine if one of them is defective?I know it wouldn't find the distortion problem but possibly the volume issue?
  Reply With Quote
Old 14th November 2007, 02:21 AM   #8
spooney is offline spooney  United States
diyAudio Member
 
Join Date: Dec 2006
I think i've found the transistors you are referring to Perry.I have a copy of the schematic.Do you think if you saw it you might be able to tell what parts were the muting transistors?
  Reply With Quote
Old 14th November 2007, 02:26 AM   #9
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Send it to me.
babin_perry@yahoo.com

Where did you get the schematic? Rockford told me that they were not available.
  Reply With Quote
Old 14th November 2007, 11:17 AM   #10
spooney is offline spooney  United States
diyAudio Member
 
Join Date: Dec 2006
I e-mailed the support department at Lightning Audio and they sent it to me the next day.I'll send you a copy of it right now.Its in PDF form.
  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
Lightning Audio 2000watt Class D confused256 Car Audio 21 5th August 2013 11:32 PM
lightning audio amp repair doughboi916 Car Audio 14 31st August 2007 10:05 PM
ATC SM75-150S & Volt B250.8 Review ralphs99 Multi-Way 5 17th July 2006 10:16 PM
Volt B250.9 Asdonk Multi-Way 2 11th September 2005 04:51 PM
class d lightning audio (rockford) 1000 watt help zfactor Class D 2 5th April 2005 09:57 PM


New To Site? Need Help?

All times are GMT. The time now is 09:44 AM.


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