audiolab 8000a - Page 4 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 November 2006, 01:28 PM   #31
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
those two aluminium plates and the three transistors sandwiched in between are probably the drivers and Vbe multiplier.

Could the burnt resistor and cap at the bottom be connected to ground? Are they the Zobel network? If so, then oscillation could be the cause.

Try to tie in the schematic to some of the PCB. Give us some clues.

edit
The two 4r7 in the middle are probably the Zobel.

What causes predrivers to blow? Shorted output stage?
Where are the drivers?
__________________
regards Andrew T.
  Reply With Quote
Old 18th November 2006, 01:30 PM   #32
diyAudio Member
 
jacco vermeulen's Avatar
 
Join Date: Oct 2004
Location: At the sea front, Rotterdam or Curaçao
Send a message via Yahoo to jacco vermeulen
Dave,

The burnt bottom resistor is the one that supplies the front end from the main rail, as on the later 8000 edition.
You can see the thick supply tracks shine through the board on both sides of the circuit, and zener diodes connected to it on both sides as well a bit further down the pcb.
It forms a low pass filter with the foil cap. next to it.
If that resistor is burnt, it means the pre-driver is dead.
Pre-driver diseased=> the corresponding driver damaged or dead too.

The lack of bigger drivers makes you wonder whether the output devices are not Darlingtons.
For regular output transistors, the minimum driver size would have to be a TO126 device.
(unless it's a mosfet output stage, which additionally would make the small TO220 devices look more natural)

The ones between the aluminium plates are flat TO92 versions, such as Zetex ZTX devices..
That leaves the outer real-TO92 ones as the drivers, likely MPSA versions as the 2d and 3d edition had.
__________________
The buck stops Here
  Reply With Quote
Old 18th November 2006, 08:17 PM   #33
diyAudio Member
 
Join Date: Nov 2006
Hi all Its difficult to follow the track but it looks like the burnt out resistors do go to the sandwiched transistors and down through the zener, i have also found another three transistors which were sandwiched by aluminium strips one which has just fell off i dont know where the other is. I will post more photos.

Thanks dave.
Attached Images
File Type: jpg line run.jpg (86.3 KB, 266 views)
  Reply With Quote
Old 18th November 2006, 08:19 PM   #34
diyAudio Member
 
Join Date: Nov 2006
photo 2
Attached Images
File Type: jpg strip.jpg (71.9 KB, 253 views)
  Reply With Quote
Old 26th November 2006, 04:28 PM   #35
diyAudio Member
 
Join Date: Nov 2006
ground control to major tom
  Reply With Quote
Old 26th November 2006, 11:25 PM   #36
diyAudio Member
 
Join Date: Nov 2006
Output devices are sm 8411 does anyone know whether they are transisor or fet, all the left side output devices are shorted plus some of the transistors fron the zoble, 4 resistors, caps are ok and zener diodes.
  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
Audiolab 8000a dantzig65 Solid State 9 6th June 2011 03:48 PM
problem with audiolab 8000a davidgale Solid State 6 12th August 2008 09:34 PM
Help! Audiolab 8000A Matthewong Solid State 9 15th October 2007 07:09 PM
Resistor for Audiolab 8000a dw887 Parts 13 26th January 2006 10:34 PM


New To Site? Need Help?

All times are GMT. The time now is 03:56 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