Behringer 1400W Class D for B1800D Repair help!! - Page 6 - diyAudio
Go Back   Home > Forums > Amplifiers > Class D

Class D Switching Power Amplifiers and Power D/A conversion

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 20th January 2014, 08:21 PM   #51
shepo1 is offline shepo1  United States
diyAudio Member
 
Join Date: Dec 2013
Yes.. they would be 180 deg out .. if both sides were working.. but if one side is not.. then the good side is just inducing a voltage to the bad side right?? And that is what im seeing at VS on the bad side. anyway..I think Im back to trying to figure out why the bad side is not starting up..
Thanks again for your input and advice...
  Reply With Quote
Old 20th January 2014, 08:37 PM   #52
diyAudio Member
 
Reactance's Avatar
 
Join Date: Jun 2005
Location: Cape Town
Quote:
Originally Posted by shepo1 View Post
Here is the schematic again.. you can see the 2 inductors sharing the core circled in blue.. for the simulation.. I basically did the circuit circled in red.. as that is what is exposed to VS.. and simulated the good side switching by using a square wave 75 V voltage source ..and then looked at the bad side VS to gnd.. you can see the result is similar to what I get on my scope..
You need to probe each node logically to find the problem.

You will get a modulation without the driver IC as the first op-amp in the loop with the two capacitors forms an integrator (this sets the oscillation frequency) followed by two logic gates producing a signal 180 degrees out of phase with each other, one phase per input of the two IC (to produce a full bridge), you can check this with the driver IC absent,they must be symmetrical and 180 degrees out of phase with each other. do this with a 1 Khz test or some test tone applied (not music for observation clarity) and see the behaviour in action.

similar to this.
Click the image to open in full size.


Have you have probed both of these switching/signal nodes from the start till the path where it enters "both drivers" at their inputs respectively.
__________________
There’s nothing worse than the smell of burned output transistors!!

Last edited by Reactance; 20th January 2014 at 08:53 PM.
  Reply With Quote
Old 20th January 2014, 09:02 PM   #53
shepo1 is offline shepo1  United States
diyAudio Member
 
Join Date: Dec 2013
Yes. I have.. I believe this to be working properly.. now, initially, the IC which creates the 180 inversion was bad. and this may have lead to the initial failure of the amp.. as it was outputting just DC.. But now. If I look at the input to the driver IC's I see the inversion at the other ic as expected .. As I mentioned before. If I pull the Bad side Driver IC.. the good side will start up and seems to cycle at about 166 KHz....If I put the bad side IC back in.. I can see the good side again start up.. I can see the induced wave on the bad side.. but the bad side causes the OC prevention to trigger and I can only see a few cycles of the 166Khz before it starts over..( I can see 1 or 2 cycles) I can see a good Gate signal on the bad side at LO ( similar to what I see in the good side) .. But seems like the bad side FET is not turning on..so it OC cycles again and so on. So I think im back to trying to figure out why the bad side continues to go into OC protection. To me it is because the FET is not conducting .. which would mean bad FET.. or possibly Gate signal is not causing fet to turn on ? I checked continuity of LO to Gate resistor and thru resistor to gate and that seems ok. maybe I can manually turn the fet on and see if its working..
  Reply With Quote
Old 24th January 2014, 11:07 PM   #54
shepo1 is offline shepo1  United States
diyAudio Member
 
Join Date: Dec 2013
HI.. well. still at it.. I have verified the feedback path is ok for both sides.. Signals to gate Driver is good, both sides.. one side is the inverse of the other. I swapped the 20957 IC's same condition. Good side fires up .. Bad side no go, and bad side causes OC cycle When I check LO gate signal on bad side.. I don't see anything. I verified LO side FET is ok. by forcing it on with +12 from VCC.. it turns on fine. SO IC is good FET is good.. It is almost like the 20957 is shutting down before it even outputs the LO side Gate signal.. or it just happens so fast I can catch it on the scope.. but I would think I would see the FET turn on .. even if for a short time.. I have check supporting components.. I cant find any thing out of tolerance.. All voltages to 20957 are good.. I'm baffled. any other ideas of why the gate signal might be weak and not turn on fet.. Maybe I will just bypass the pcb trace and wire it directly for a test.. that's all I can think of.. Grrrr.
  Reply With Quote
Old 30th January 2014, 07:46 AM   #55
shepo1 is offline shepo1  United States
diyAudio Member
 
Join Date: Dec 2013
HI.. Guess what .. ITS FIXED.. finally.. my god.. that was a tough one.
after many 20957 ic's and MOSFET's destroyed.. i finally got it.. Thanks all for your input and advice.
For anyone who cares.. this thing had multiple issues. Not sure what i caused or if one thing caused the next to be damaged.. But
initially, H04 ic ( the one that inverts the input to the 20957 ic for full bridge operation) was bad and just outputting DC. ( I think this was damaged when one of the 20957 ics fried) but not sure. FETS were shorted on one side. also 20955 ic was toast on same side. I replaced all those parts and then amp would just OC cycle. Found one side was not starting up.. the other was.. Just FYI The strange wave forms i was getting on the bad side VS and I posted earlier were due to the good side inducing voltage thru the common core inductor to the bad side. After many diffrent tests and trying diffrent things, I Finally figured out the HO signal was not turning on the High side FET on the bad side. Thought fet was bad but tested by manually turning on.. It worked ok so back to the IC being bad.. Replaced IC again.. still same.. WTF.. seemed like there wasn't enough current to turn fet on.. 12V supply was good SO i swapped Boot strap caps from bad side to good.. and now Bad side is ok!!! and Good side bad.. SO.. Boot strap CAP was no good.. It didn't really test bad though.. so. Tested like normal cap using ohm meter.. It was just kind of the last thing i could think of to try. Anyway.. replaced boot strap Cap and now both sides start up and everything is working.. Finally.. Well I learned a lot.. and hope my experiences are helpful to some one else here. Thanks again for all your input and ideas.. they were quite helpful..
  Reply With Quote
Old 31st January 2014, 10:20 PM   #56
diyAudio Member
 
Reactance's Avatar
 
Join Date: Jun 2005
Location: Cape Town
Quote:
Originally Posted by shepo1 View Post
HI.. Guess what .. ITS FIXED.. finally.. my god.. that was a tough one.
after many 20957 ic's and MOSFET's destroyed.. i finally got it.. Thanks all for your input and advice.
For anyone who cares.. this thing had multiple issues. Not sure what i caused or if one thing caused the next to be damaged.. But
initially, H04 ic ( the one that inverts the input to the 20957 ic for full bridge operation) was bad and just outputting DC. ( I think this was damaged when one of the 20957 ics fried) but not sure. FETS were shorted on one side. also 20955 ic was toast on same side. I replaced all those parts and then amp would just OC cycle. Found one side was not starting up.. the other was.. Just FYI The strange wave forms i was getting on the bad side VS and I posted earlier were due to the good side inducing voltage thru the common core inductor to the bad side. After many diffrent tests and trying diffrent things, I Finally figured out the HO signal was not turning on the High side FET on the bad side. Thought fet was bad but tested by manually turning on.. It worked ok so back to the IC being bad.. Replaced IC again.. still same.. WTF.. seemed like there wasn't enough current to turn fet on.. 12V supply was good SO i swapped Boot strap caps from bad side to good.. and now Bad side is ok!!! and Good side bad.. SO.. Boot strap CAP was no good.. It didn't really test bad though.. so. Tested like normal cap using ohm meter.. It was just kind of the last thing i could think of to try. Anyway.. replaced boot strap Cap and now both sides start up and everything is working.. Finally.. Well I learned a lot.. and hope my experiences are helpful to some one else here. Thanks again for all your input and ideas.. they were quite helpful..
congratulations, you could have saved some money/parts had you understood the working of the bootstrap section in more detail as advised previously

oh well have a good time with the amplifier.
__________________
There’s nothing worse than the smell of burned output transistors!!
  Reply With Quote
Old 29th March 2014, 10:56 AM   #57
diyAudio Member
 
Join Date: Mar 2014
Hi fellows audio enthusists,
Have (almost) similar problem with class D audio amp, BEHR B1500D.
Schematics looks similar as in your case.
May I ask for whole schematics , beside MAINBOARD which I collected already from this issue?
Thanks in advance.
Todor,Macedonia
  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
12v to 70v 1400w what do you think? Alexontherocks Power Supplies 19 31st March 2014 08:51 AM
1400w amp in 4 ohms dell Solid State 18 25th May 2013 09:56 AM
Behringer B1800D-PRO 10-30Hz low bass extension AndreaT Subwoofers 44 20th September 2012 09:57 AM
Behringer Class D for less sampleaccurate Class D 17 6th February 2011 11:44 PM
Help with class D repair please xokia Class D 3 26th October 2004 03:22 PM


New To Site? Need Help?

All times are GMT. The time now is 07:29 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