Nakamichi PA-7II won't power on, limiter resistor blown - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

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 12th June 2015, 08:24 PM   #1
diyAudio Member
 
Join Date: Mar 2015
Default Nakamichi PA-7II won't power on, limiter resistor blown

I've come across a non-functional Nakamichi PA-7II amp. It will not power on. I found that R504, the 20W resistor on the limiter PCB is blown. So I replaced it, and it immediately blew again. The thermal fuse in series with it is intact. Does anyone have any ideas as to what might be causing the resistor to blow?
  Reply With Quote
Old 12th June 2015, 09:50 PM   #2
gasgeek is offline gasgeek  United States
diyAudio Member
 
Join Date: Aug 2012
Location: SO CAL
Most likely the power transformer is shorted. R504 is acting as an inrush limiter until the relay kicks-in which is supplied by a secondary voltage from the transformer.
  Reply With Quote
Old 12th June 2015, 10:10 PM   #3
diyAudio Member
 
JonSnell Electronic's Avatar
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
Send a message via Skype™ to JonSnell Electronic
Or a short circuit on a secondary winding.
Disconnect the secondaries and power it up with the 60W light bulb to replace the resistor.
__________________
Support for Flying Mole, Allen & Heath, Valve amps, older designs & 2CVs. www.jonsnell.co.uk
  Reply With Quote
Old 13th June 2015, 01:07 AM   #4
diyAudio Member
 
Join Date: Mar 2015
Wow, the power transformer would be difficult to replace I imagine. Can I just check for shorts on certain wires to/from the transformer?
  Reply With Quote
Old 13th June 2015, 06:56 PM   #5
wayne is offline wayne  United States
In the hills
diyAudio Member
 
Join Date: Jan 2002
Location: Northern California
Disconnect secondary from rectifiers as a test.
__________________
wizards assistant
  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
Nakamichi PA-7II: Thermofuse in the potted transformer electrafixion71 Pass Labs 31 3rd January 2015 02:31 AM
Limiter Resistor of MOSFET Power Amp ervinl Solid State 11 23rd July 2010 06:55 AM
Nakamichi PA-7II manuals - HELP Peteb Pass Labs 4 4th October 2007 07:09 PM
Nakamichi OMS-7II help proteo01 Digital Source 0 17th September 2007 03:12 AM
Nakamichi PA-7 Power Transformer sourceoneaudio Solid State 0 22nd December 2006 03:53 PM


New To Site? Need Help?

All times are GMT. The time now is 07:47 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright 1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2