Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Alpine MRV-F540 - Channel 4 problems
Alpine MRV-F540 - Channel 4 problems
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 27th July 2017, 06:58 PM   #1
mojozoom is offline mojozoom  United States
diyAudio Member
 
Join Date: Feb 2013
Location: Kansas City
Default Alpine MRV-F540 - Channel 4 problems

Channel 4 of my Alpine MRV-F540 was a little scratchy so Ipulled it from the car and set it aside for a few years. Now I'm trying todiagnose the problem.

I checked the DC offset of each output, and all are < 3mV except for channel 4, which measured about 21 mV. After that I checked thesignals entering and exiting the crossover boards, and all of the channels areabout the same, so I'm assuming the problem is elsewhere.

In checking the voltages on each leg of the outputtransistors it's apparent that channel 4 is different than the other channels,and out of balance. Here's what they look like:


Click the image to open in full size.


Click the image to open in full size.



Click this link to see the schematic close up: https://photos.app.goo.gl/pieLZonPvrOAuiHs2


And here's what they measure like. I'm powering this with12VDC to do these tests, so I expect that the 29.17 VDC voltage on thecollector is probably due to that as the service manual uses 14.4VDC fortesting.

Ch4 Ch3 Spec
E -0.0212 0.0019 0.00
C 29.18 29.17 34.6
B 0.425 0.447 0.45

B -0.398 -0.376 -0.38
C 0.978 1.000 1.04
E -1.021 -0.997 -1.04

E -0.0212 0.0016 0.00
C -29.18 -29.17 -35.2
B -0.474 -0.451 -0.45


Is there a typical problem point that would cause these to be out of balance? There's no bias pot that I can find on the schematic or on the board, though I haven't pulled the board out yet to look at the back side. Thanks!
Attached Images
File Type: jpg schematic.JPG (272.2 KB, 35 views)
  Reply With Quote
Old 27th July 2017, 07:18 PM   #2
Perry Babin is offline Perry Babin  United States
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Q459 is what generally causes offset issues. It's part of the differential amplifier. If it's easy to swap with the corresponding part from another channel, you could see of the offset follows the transistor.
  Reply With Quote
Old 31st July 2017, 06:06 PM   #3
mojozoom is offline mojozoom  United States
diyAudio Member
 
Join Date: Feb 2013
Location: Kansas City
Oops.

These little 2SK2145 SMD JFET guys have 5 leads, and afterdesoldering with wick I was gently prying each of the leads up with an Exactoto make sure they were completely desoldered and it went "Pop!" and flew up and behind my workbench into the pitof eternal peril. All of the SMD stuff on this amp is stuck down to the board with these little redadhesive blobs and they don't want to let go without a fight.

The data sheet for the 2SK2145 makes me feel like we shouldexpect them to fail pretty regularily:
"Using continuously under heavy loads (e.g. theapplication of high temperature/current/voltage and the significant change intemperature, etc.) may cause this product to decrease in the reliabilitysignificantly even if the operating conditions (i.e. operating temperature/current/voltage,etc.) are within the absolute maximum ratings."

The Alpine service manual calls out 2SK2145 - Y GR BL forthese, so I'm assuming that means it can use any of those three versions.Evidently that suffix indicates the "Drain Current" IDSS classification,as follows
Y: 1.2 to 3.0 mA,
GR: 2.6 to 6.5 mA,
BL: 6.0 to 14.0 mA
DigiKey stocks both the Y and the GR versions, should Ifavor the Y version with the lower drain current?

I'll order four of them and swap them all out, as thatwarning on the data sheet makes me wonder if the others aren't far behind.
  Reply With Quote
Old 31st July 2017, 07:50 PM   #4
Perry Babin is offline Perry Babin  United States
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Order both versions and extras of all.

The transistor generally has markings for hfe.
  Reply With Quote
Old 19th August 2017, 02:05 AM   #5
mojozoom is offline mojozoom  United States
diyAudio Member
 
Join Date: Feb 2013
Location: Kansas City
We'll I replaced all four of the little buggers. My soldering isn't as nice as the original, but I only had one bridge that needed fixing and all was well. I went with the GR version of the little FETs, as that was what DigiKey had the most of. I was able to determine that the original ones were the Y version.

After the repairs CH4 is measuring only 4.5 mV of offset, which is way better (it used to be 21 mV). All of the legs of the output transistors are balanced now - yay!

The other channels vary from 0.1 to about 2.8 mV, so Ch4 isn't too far. Maybe some other component was taking too much heat when everything was out of balance. I'll look over the schematic some more to see if I can figure out where that could be coming from just for fun.

I'll give it a full power sound test this weekend. Thanks for your help Perry!
  Reply With Quote

Reply


Alpine MRV-F540 - Channel 4 problemsHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
AUIRF3205 versus IRF3205 for Alpine MRV-F540 mojozoom Car Audio 13 23rd July 2017 11:54 PM
mrv f540 DREW028 Car Audio 2 30th November 2015 06:27 PM
Alpine mrv f357 problems rdfenn3 Chip Amps 0 30th March 2013 07:42 AM
Alpine MRV-F400 channel 3 no output loginfailed Car Audio 6 16th December 2007 03:06 AM
Alpine MRV-F400 op amp problems? spooney Car Audio 8 27th November 2007 04:15 AM


New To Site? Need Help?

All times are GMT. The time now is 04:02 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki