old first amp - 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 30th September 2011, 12:26 PM   #1
rrae is online now rrae  Norway
diyAudio Member
 
Join Date: Mar 2011
Default old first amp

I believe it's first austria amp with model fa 4410. I can't get sound. There is no voltage on middle legg for output transistors. Power transistors are IRFZ44N's, one is shorted.
I believe these diodes in picture, are zeners 1n4744? Am I right? One is shorted, and I want to replace.
I think amp is in protection mode, but protection light is not on, only power light. I can post voltages from KIA494P.
Sorry for no macro, if need I can take good macro from any place of PCB.
Attached Images
File Type: jpg 21.JPG (476.6 KB, 159 views)
__________________
scope,dmm,cd

Last edited by rrae; 30th September 2011 at 12:28 PM.
  Reply With Quote
Old 30th September 2011, 12:46 PM   #2
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
If they're connected between the base and emitter of the PNP driver transistor, they're likely 1N4148s or the equivalent.

I'm assuming that you've already replaced the shorted FET.

Do you have both positive AND negative rail voltage on the center legs of the output transistors?

Do you have both positive and negative regulated voltage on the power supply pins of the op-amps?

Have you tried operating all pots and switches through their entire range with speakers connected to see if it ever produced any sound (any type of sound, audio, noise...)?
  Reply With Quote
Old 30th September 2011, 01:54 PM   #3
rrae is online now rrae  Norway
diyAudio Member
 
Join Date: Mar 2011
I didn't test for audio. I want to replace these failed components. 1n4148 look smaller than that diode on board.
__________________
scope,dmm,cd
  Reply With Quote
Old 30th September 2011, 02:03 PM   #4
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
The diodes may (should) have numbers on them. Desolder them and see if you can read the numbers.

The 4744 is a Zener diode and would not be connected as I described.

Do the solder connections on the board appear to be original?
  Reply With Quote
Old 30th September 2011, 03:14 PM   #5
diyAudio Member
 
Join Date: Jul 2004
Location: Edmonton, AB Canada
In your pic, the upper little diodes look like clamps for the gate drive on the SMPS. They rarely fail. Check Q512 and neighbor are probably shorted and giving you a misleading reading.

1N914/1N4148 are the same size but a bit low current, I would guess a fast-recovery diode like a 1N4935 would be tougher.

Note that zener diodes show zener symbol on pcb (see ZD502 silver far right, 1/2W)
  Reply With Quote
Old 1st October 2011, 05:39 PM   #6
rrae is online now rrae  Norway
diyAudio Member
 
Join Date: Mar 2011
Well, replaced diode, and power transistors. I got rail voltage in outputs.
__________________
scope,dmm,cd
  Reply With Quote
Old 1st October 2011, 05:59 PM   #7
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
What did you use as a replacement for the diode?
  Reply With Quote
Old 1st October 2011, 06:23 PM   #8
rrae is online now rrae  Norway
diyAudio Member
 
Join Date: Mar 2011
1n4148 is used for replacement. There wasnt any numbers or marks on old diode which i desoldered from board.
__________________
scope,dmm,cd
  Reply With Quote
Old 2nd October 2011, 11:29 AM   #9
rrae is online now rrae  Norway
diyAudio Member
 
Join Date: Mar 2011
Well, I replaced KIA494P with TL494CN, and it goes in protection mode, with KIA it didnt went in protection.
__________________
scope,dmm,cd
  Reply With Quote
Old 2nd October 2011, 11:32 AM   #10
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
There's no reason for the amp to go into protect with the TL494. They're supposed to be identical in function.

If you can't find the fault, post the DC voltage on all 16 pins of the 494.

Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 15:
Pin 16:
  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
Modify & build out (2) Western Electric 300B / 2A3 Hammond monoblock amps & UTC LS-5 quality sound Tubes / Valves 0 9th May 2009 03:59 PM
Krell KSA 80 bias & dc offset check & adjust procedure Clouseaupte Solid State 3 9th August 2007 09:39 AM
DIY-AMP <ZAS> Low THD & IM high bandwith murphy Solid State 18 30th December 2005 10:28 AM


New To Site? Need Help?

All times are GMT. The time now is 03:51 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