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

Solid State Talk all about solid state amplification.

Repairing NAD7225pe one channel faulty
Repairing NAD7225pe one channel faulty
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 11th January 2019, 11:40 AM   #1
heol is offline heol
diyAudio Member
 
Join Date: Dec 2018
Default Repairing NAD7225pe one channel faulty

Hello

My first post here. Be gentle please

I have NAD7225pe with one channel not working, it is my first attempt in repairing a amplifier.
Tested all transistors in output stage on faulty channel and replaced all faulty transistors which were output transistors Q415 and Q417, 2N3055 and MJ2955 (from Mouser) also both drivers Q411 and Q413 which were replaced with MJE253G and MJE243G.
Also bias transistor Q409 BD139.
Other transistors tested ok and diodes.
Caps look ok. I cannot find short in any of them.

burned 180 ohm resistor also replaced.

Also added 0.22 ohm 3W resistors to emitters on both Q417 and Q415 also base resistor 6.8 ohm.

Using dim bulb tester for initial turn on and the 70W bulb lights up brightly.
Can it be the cause that bias is not adjusted the reason it draws so much current it lights up the 70 W bulb?
Can I adjust the bias levels with the dim bulb tester connected?
Attached Images
File Type: png nad7225pe_output.png (231.7 KB, 52 views)
  Reply With Quote
Old 11th January 2019, 12:39 PM   #2
JonSnell Electronic is online now JonSnell Electronic  United Kingdom
diyAudio Member
 
JonSnell Electronic's Avatar
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
I would remove the 0.22R resistors as this design does not use them. Remove the bias current link and measure the bias current, setting it to around 15mA or 15mV across R455. Check the DC voltage between the bases of Q411/413.

180R burnt? Where is that? 6R8 resistors? Where?
__________________
Support for Fender, Marshall and all Valve Equipment; Audio Innovations, Audiorama FU29, Quad and Leak. www.jonsnell.co.uk
  Reply With Quote
Old 11th January 2019, 01:29 PM   #3
heol is offline heol
diyAudio Member
 
Join Date: Dec 2018
Sorry, R453 was burnt (180 Ohm).

I saw a thread on this forum which was also same receiver.
On that thread it was recommended to add resistors to both emitters on output transistors because newer transistors would require them.
On same thread it is also talked about base resistor on both output transistors so I added them as well (6.8 ohm).
Help NAD 7225PE (3020) receiver output transistors replacement

When you say bias current link you are talking about the solder short across R455?
  Reply With Quote
Old 20th January 2019, 09:01 PM   #4
heol is offline heol
diyAudio Member
 
Join Date: Dec 2018
Can I do voltage measurements with DBT connected? Doesn't lower supply voltage and voltage will be lower?

Anyway I measured B-E Voltage on output transistors Q411 and Q417 it is 0.72V and 0.75V compared to good channel it is around 0.3V.
So these Q415 and Q417 are in ON state.

Turning R443 (biasing resistor) to see if it would lower the B-E voltage it did have no effect.

Does anyone have an advice to for me where I should look next?
  Reply With Quote

Reply


Repairing NAD7225pe one channel faultyHide 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
lab gruppen 1600 faulty channel B discjockeyr PA Systems 38 26th November 2018 08:21 PM
FS: Denon POA-2400 one channel faulty, EU jlithen Swap Meet 1 2nd February 2017 11:24 AM
CD Player faulty output channel ? Konzentr8 Digital Source 8 27th June 2016 04:03 PM
Quad 34 faulty channel Elliotaw Solid State 0 27th April 2011 02:27 PM
Cyrus Two - Faulty Speaker Channel Hedley Solid State 0 30th January 2008 11:57 PM


New To Site? Need Help?

All times are GMT. The time now is 05:01 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki