Fake transistors? - 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 15th February 2008, 11:27 PM   #1
spooney is offline spooney  United States
diyAudio Member
 
Join Date: Dec 2006
Default Fake transistors?

I've repaired the same alpine MRV-1000 amplifier twice now.The first time I replaced the 2sa1265's in the bad channel and all was well for about a month.After the amp died this first time I replaced the 2sa1265's as well as the 2sc3182's in the bad channel.The amp worked great... for about a day. I'm starting to wonder if these transistors that I purchased are up to spec.The place I purchased them from doesn't specify what brand they are anywhere even on the packing slip.All of the transistors that have failed were purchased from the same place at the same time.Not surprisingly these parts were cheaper than any other ones I could find.Does anyone else here have any experience or comments about www.electronix.com ?Both times when the amp failed it was not even at full tilt or warm at all for that matter.I don't see anything else wrong with this amp except that now that the parts have failed again the 10 ohm resistors connected to the first leg of the 2sa1265's appear to be out of tolerance.I'm kinda just scratching my head on this one at this point. I'd like to buy parts from a more reliable supplier and give it another shot but at the same time i'd rather not throw 15 to 20 dollars in parts down the toilet again.
  Reply With Quote
Old 15th February 2008, 11:52 PM   #2
spooney is offline spooney  United States
diyAudio Member
 
Join Date: Dec 2006
I have some FJA4210 and FJA4310 transistors here and the ratings are similiar to the 2sa1265 and 2sc3182. Does anyone know if these would make for a suitable replacement?
  Reply With Quote
Old 16th February 2008, 01:59 AM   #3
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Those look like a viable substitute. If you try them, you need to set the biasing when cold. Then heat the amp up (by playing it) checking the biasing every few minutes to make sure it's not creeping up. You need to do this until it reaches thermal shutdown.

Pop open the transistors and take a detailed photo of the internals. If you don't have a good camera, a flatbead scanner should do a good job. Post the photo here. It will allow others to compare them in the future.

If there's any demand for it, I could post them on my site. I'd be willing to photograph the ones that I remove from various amps to allow other to compare to suspected fakes.
  Reply With Quote
Old 16th February 2008, 03:32 AM   #4
diyAudio Member
 
Join Date: Dec 2007
Location: Phoenix, AZ
Hello Spooney, Mr. Elliot doesn't directly address the transistors you have, at least I didn't see them, but he does give a good idea of how to check out the transistors you have. Here's the weblink:

http://www.sound.westhost.com/counterfeit.htm


Peace,

Dave
  Reply With Quote
Old 16th February 2008, 09:21 AM   #5
spooney is offline spooney  United States
diyAudio Member
 
Join Date: Dec 2006
Perry I've never had to set the bias on an amplifier.How do I go about doing so?Can it be done with a multimeter alone?
  Reply With Quote
Old 16th February 2008, 09:26 AM   #6
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Did you not replace the driver transistors?
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 16th February 2008, 01:23 PM   #7
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Looking at the schematic, it appears that it doesn't have bias pots.

To determine if the bias current is remaining constant, you can measure the DC voltage across the emitter resistors. From the ampguts page, it appears that the legs of the resistors are not accessible. Measuring the voltage from the emitter of a 2SA1265 to the emitter of a 2SC3182 (both from the same channel) is the same as measuring across 2 emitter resistors.

Compare the good channel to the channel you repaired. If they're approximately the same, begin warming up the amp and monitor the voltage on the channel you repaired. You'll need to measure the voltage from emitter to emitter with no signal.

You'll need to set your meter to the most sensitive range. If there is any voltage across the emitters, it will be well below 0.01v.
  Reply With Quote
Old 16th February 2008, 01:51 PM   #8
spooney is offline spooney  United States
diyAudio Member
 
Join Date: Dec 2006
did some more poking around and I see that the 10 ohm base resistors are fine,they were just thrown off because of the bad transistors but I see that the IRFZ44N's in the power supply have died again.The amp was pretty much in this same condition when I received it originally. the power supply fets survived the last blowout but did not make it this time. If the driver transistors are the small ones mounted to the heatsink near the outputs then yes I did replace them. I'll have to order more IRFZ44N's before I give this thing another shot as I only have two on hand at the moment.I'll try to get some pics later today of the inside of those transistors.
  Reply With Quote
Old 16th February 2008, 01:58 PM   #9
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
Use a 15A fuse (or the smallest size that does not blow during normal use) and you will get less IRFZ44 fried (if any)
__________________
I use to feel like the small child in The Emperor's New Clothes tale
  Reply With Quote
Old 16th February 2008, 02:58 PM   #10
sdoom is offline sdoom  Germany
diyAudio Member
 
Join Date: Mar 2004
Location: Heidelberg
I recommend a 2 Ohm resistor (something around 20W or bigger ) in line with the +12V power line , a 15A fuse needs too long to fry and the IRFZs may be damaged until the fuse blows.

If you want to use a fuse dont use bigger fuses than 5A , that will do the job until you fixed the amp to that state it can be really driven into higher power .

For a lot of my repair jobs I used BD249 / BD250 (TIP35 &TIP36 in USA) for analog amplifiers. usually i got those from Texas instruments (cost about 2 USD each overhere). Once I got cheap BD249 (50cents a piece) and they turned out to fail at higher currents so I used those for replacements in smaller korean amplifiers (most of the times the cheap amps already came with cheap transsitors.... )
  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
More Fake Transistors DieterD Solid State 43 30th October 2011 08:26 AM
fake transistors gain Solid State 14 28th April 2008 02:12 PM
Fake transistors? alexan Parts 3 28th December 2006 02:26 PM
fake transistors tinkerbell Solid State 17 19th January 2006 11:51 AM
Fake Transistors MGR Solid State 10 28th October 2002 10:46 AM


New To Site? Need Help?

All times are GMT. The time now is 04:39 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