MTX JH1200 - 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 18th April 2012, 02:03 AM   #1
RiLoWa is offline RiLoWa  United States
diyAudio Member
 
RiLoWa's Avatar
 
Join Date: Aug 2010
Location: Illinois
Default MTX JH1200

I found that two IRF640N outputs (FET404 & FET6) were shorted, one on each side. I removed all fourteen to find the two, checking each one. None of the remaining twelve appear to be leaking. The TIP29C & TIP30C were checked in circuit, and are not shorted. All of the 10 Ohm gate resistors are ok. I presume the .1 Ohm, 5W resistors are ok, none are even remotely discolored.

I re-installed all of the IRF640Ns that appear ok and left out the two shorted ones at those above FET locations. The amp draws excessive current. I removed the four rectifiers and the amp idles at ~2A draw. Is that high for an unloaded power supply?

Does this amp require all fourteen of the outputs to be good and installed or are there more areas I need to look at?
__________________
Tools - 1. TPI Scope Plus 440 2. B&K 2125 20MHz Dual Trace 3. Sorensen DCR20-50B 4. B&K 4011 5MHz Function Generator 5. Weller WESD51 6. A big hammer
  Reply With Quote
Old 18th April 2012, 02:12 AM   #2
ivkata is offline ivkata  United States
diyAudio Member
 
Join Date: Dec 2010
replace all of them another one might be burned inside but not appearing shorted
  Reply With Quote
Old 18th April 2012, 05:11 AM   #3
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Did you check the components on the driver board? They often fail when the outputs fail.

I would expect the amp to work with one transistor missing from each side.

2A is high but doesn't necessarily mean that there is a problem.
  Reply With Quote
Old 18th April 2012, 01:22 PM   #4
RiLoWa is offline RiLoWa  United States
diyAudio Member
 
RiLoWa's Avatar
 
Join Date: Aug 2010
Location: Illinois
I checked the A92s and A42s in circuit and they are not shorted.

Should I check the smaller components?
__________________
Tools - 1. TPI Scope Plus 440 2. B&K 2125 20MHz Dual Trace 3. Sorensen DCR20-50B 4. B&K 4011 5MHz Function Generator 5. Weller WESD51 6. A big hammer
  Reply With Quote
Old 18th April 2012, 01:58 PM   #5
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
How much was the excessive current draw?

Did it draw excessive current as soon as remote voltage was applied?
  Reply With Quote
Old 18th April 2012, 02:13 PM   #6
RiLoWa is offline RiLoWa  United States
diyAudio Member
 
RiLoWa's Avatar
 
Join Date: Aug 2010
Location: Illinois
It does blow a 25A fuse shortly (~1.5 seconds) after remote voltage is applied. Once the draw begins, it climbs rapidly. I think it was close to ~30A when fuse blew.

With a limiting resistor in line with B+, the amp cycles on and off because the voltage drops too low for the amp to stay on but it does not blow a 15A fuse this way.
__________________
Tools - 1. TPI Scope Plus 440 2. B&K 2125 20MHz Dual Trace 3. Sorensen DCR20-50B 4. B&K 4011 5MHz Function Generator 5. Weller WESD51 6. A big hammer
  Reply With Quote
Old 18th April 2012, 02:55 PM   #7
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
When it's cycling on and off, do you see rail to rail oscillation on any legs of the output transistors?
  Reply With Quote
Old 18th April 2012, 04:16 PM   #8
RiLoWa is offline RiLoWa  United States
diyAudio Member
 
RiLoWa's Avatar
 
Join Date: Aug 2010
Location: Illinois
I have not checked for that yet.

Where should I place the scope ground in this amp when I do?
__________________
Tools - 1. TPI Scope Plus 440 2. B&K 2125 20MHz Dual Trace 3. Sorensen DCR20-50B 4. B&K 4011 5MHz Function Generator 5. Weller WESD51 6. A big hammer
  Reply With Quote
Old 18th April 2012, 05:24 PM   #9
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
You can probably use the primary ground.
  Reply With Quote
Old 19th April 2012, 01:07 AM   #10
RiLoWa is offline RiLoWa  United States
diyAudio Member
 
RiLoWa's Avatar
 
Join Date: Aug 2010
Location: Illinois
I re-installed the rectifiers.

With my 3 Ohm resistor and a 15A fuse in line with B+ the power light comes on with ~4 amp draw, however the voltage at the amp's terminals is ~8.5VDC and does not change much as I adjust my power supply from 12V-16V.

Testing any of the three legs of the output located at FET18 shows nothing on the scope.
__________________
Tools - 1. TPI Scope Plus 440 2. B&K 2125 20MHz Dual Trace 3. Sorensen DCR20-50B 4. B&K 4011 5MHz Function Generator 5. Weller WESD51 6. A big hammer
  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
MTX 6500D mike49504 Car Audio 16 26th September 2011 11:34 PM
orion hcca250r, kicker zr 1000, mmats d800.2, mtx 6500d, mtx 942, rockford punch 45, ernie cosillos Swap Meet 3 12th February 2011 11:14 AM
MTX JH1200 burned resistor R140-R141 & R142 joselorenzo Car Audio 0 27th December 2009 07:18 AM
Help me fix MTX 152 and MTX 500D hakentt Car Audio 94 8th December 2008 06:26 PM
mtx pro752 2020audio Car Audio 3 3rd June 2007 06:31 AM


New To Site? Need Help?

All times are GMT. The time now is 09:17 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